Bulletin ILLINOIS NATURAL HISTORY SURVEY Bulletin Printed by Authority of kf A Comparative Study of Bird Populations in Illinois, 1906-1909 and 1956-1958 RICHARD R. GRABER JEAN W. GRABER STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION NATURAL HISTORY SURVEY DIVISION Urbana, Illinois ILLINOIS NATURAL HISTORY SURVEY Bulletin Volume 28, Article ?> Printed by Authority of October, 1963 the state of Illinois A Comparative Study of Bird Populations in Illinois, 1906-1909 and 1956-1958 RICHARD R. GRABER JEAN W. GRABER STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION NATURAL HISTORY SURVEY DIVISION Urbana, Illinois View of floodplain in Pope County, southern Illinois, 1907 and 1963. Upper picture taken from cliff 1 mile east of Browiifield, June 27, 1907, by Alfred O. Gross. Lower picture, same area as upper picture; taken May 19, 1963, by Jean W. Graber. Sev- eral of the cultivated fields of the upper picture have been filled in with forest. Tree growth conceals the railroad tracks visible in the foreground of the upper picture. -mmmspmU' ^'7 "' ^'Otled hills m Hard.n Count>, southern lll.m.is, 1907 ^nd I%3L pper picture taken from the east edge of Shetlerville, June 29 1907 hv AlfredLower picture, same area as upper picture; talen May 1 ' ' C). (jross. 7^k:,. „ il r ' , "" "I'l'^' f'<-iuic, ici.Kcii iviav i9, 1963, l)v Richard R (Jrahpi-Ih.s a.ea shows fewer changes in a half century than most Illinois arlas'^censti'ed U>erg.azedpasture has replaced cultivated fields shown in "th e upper picture. Landscape in Mason County, central Illinois, 1907 and 1963. Upper picture taken one-half mile east of Poplar City, May 2, 1907, by Alfred O. Gross. Similar sandy wasteland with cacti is still found in small areas in the vicinity of the Illinois River. Such areas, if undisturbed, eventually become stabilized by grass. Lower picture, same area as upper picture ; taken May 14, 1963, by Richard R. Graber. Sand prairie develops in relatively undisturbed areas in the vicinity of the Illinois River. C () N T H N T S Methods 383 Forbes-Gross Strip Census 383 Evaluation of Strip Census 389 Weather Patterns of Census Years. 393 Bird Populations in Summer Habitats 396 Cornfields (Summer) 397 Soybean Fields (Summer) 401 Plowed Fields (Summer) 401 Oat Fields (Summer) 401 Wheat Fields (Summer) 407 Pastures (Summer) 408 Ungrazed Grasslands (Summer) 412 Fallow Fields (Summer) 413 Mixed Hayfields (Summer) 414 Clover Fields (Summer) 418 Red Clover 418 Sweet Clover 420 Alfalfa Fields (Summer) 421 Marshland (Summer) 422 Shrub-Grown Areas (Summer) 424 Orchards (Summer) 429 Forests (Summer) 430 Urban Residential Areas (Summer) . .436 Comparison of Data for Summer Habitats 437 Number of Birds 438 Number of Species 439 Statewide Summer Populations 440 Bird Populations in Winter Habitats 443 Cornfields (Winter) 443 Soybean Stubble (Winter) 447 Plowed Fields (Winter) 448 Small Grain Stubble Fields ( Winter ). 448 Wheat Fields (Winter) 449 Pastures (Winter) 451 Fallow Fields (Winter) 452 Hayfields (Winter) 452 Shrub Areas (Winter) 452 Forests (Winter) 453 Comparison of Data for Winter Habitats 453 Number of Birds 456 Number of Species 456 Statewide Winter Populations 456 Account of Species 458 Avifaunal Differences Between Censuses 463 Annotated List of Common Species. .463 Turkey Vulture 464 Red-Tailed Hawk 464 Sparrow Hawk 465 Bobwhite 466 Killdeer 467 Upland Plover 468 Mourning Dove 469 Cuckoos 472 Chimney Swift 472 Yellow-Shafted Flicker 473 Red-Bellied Woodpecker 474 Red-Headed Woodpecker 474 Downy Woodpecker 475 Eastern Kingbird 476 Horned Lark 477 Barn Swallow 478 Blue Jay 479 Common Crow 480 Chickadees 481 Tufted Titmouse 482 Mockingbird 483 Catbird 483 Brown Thrasher 484 Robin 485 Eastern Bluebird 486 Starling 486 Yellowthroat 487 House Sparrow 488 Bobolink 489 Meadowlarks 489 Redwinged Blackbird 490 Orchard Oriole 491 Common Grackle 492 Brown-Headed Cowbird 492 Cardinal 493 Indigo Bunting 494 Dickcissel 495 American Goldfinch 495 Savannah Sparrow 496 Grasshopper Sparrow 496 Vesper Sparrow 497 Lark Sparrow 497 Slate-Colored J unco 497 Tree Sparrow 498 Chipping Sparrow 498 Field Sparrow 498 Song Sparrow 499 Lapland Longspur 500 Discussion 500 Events Previous to 1800 501 Development of Managed Habitats. . 502 Specific Changes in Avifauna 503 Specialization in Managed Habitats. . 504 Population Density and Avifaunal Variety 507 Population Changes and Latitude. . . .508 Range Extensions 508 Habitats and the Future of the Avifauna 509 Man and the Avifauna 515 Literature Cited 516 Index 519 Tins paper is printed hy authority of the State of Illinois, IRS Ch. 127, Par. 5S.12. It is a contribution from the Section of Wildlife Research of the Illinois Natural History Survey. Dr. Richard R. Graher is Wildlife Associate ivith that section. Dr. Jean W. Graher is Resear(h Associate in Animal Science, University of Illinois. (7498.'. -6500—6-6:'.) o^i^fe)o2 Landscape in Sanjfamon County, central Illinois, 1907 and 1962. Upper picture taken one-fourth mile north of Buffalo Hart, June 24, 1907, by Alfred U. Gross. Cornfields have comprised the largest Illinois habitat for at least the past 100 years. Lower picture, same area as upper picture; taken August 2, 1962, by James S. Ayars. Soy- beans (left foreground) came into wide use after 1920 and by 1957 occupied about 5,000,00(1 acres of Illinois land. A Comparative Study of Bird Populations in Illinois, 1906-1909 and 1956-1958 RICHARD R. G R A B E R J E A \ \V. G R A B E R On August 29, 1906, Alfred (). Gross and Howard A. Ray, working for the Illinois State Laboratory of Natural His- tory (a parent organization of the Illinois Natural History Survey) under the di- rection of Stephen A. B\)rbes, began a series of statewide, cross-country censuses of birds in Illinois. These censuses were continued at intervals until September, 1909, and the data collected were pub- lished in a series of papers (Forbes 1907, 1908, 1913; Forbes & Gross 1921, 1922, 1923) that provided a quantitative record of the Illinois bird populations of that period and a potential basis for evaluating the adjustment of bird populations to a changing environment. In 1956—1958, we conducted statewide censuses similar to those of the 1906-1909 survey. In this paper we present an analysis of our field data and compare these data with those from the first surve>'. For suggesting and encouraging this study we are indebted to Dr. Harlow B. Mills and Dr. Thomas G. Scott of the Illinois Natural History Survey. Mr. Ronald F. Labisky of the Survey provided data on pheasant populations in a study area near Sibley, Illinois. Mr. John Ames and Mr. Herbert Brucker, both of Sibley, permitted us to establish and use special study areas on their lands. Mr. John Hill, Urbana, checked some of our calculations. We are particularly grateful to Dr. Alfred O. Gross, Emeritus Professor of Biology at Bowdoin College, who pre- sented us with all of the original field notes, journals, and photographs made on the first series of strip censuses conducted in Illinois (1906-1909) and encouraged our follow-up study. Finalh , we are in- debted to Mr. James S. Avars of the Illi- nois Natural History Survey, who edited the manuscript. METHODS For an excellent review and discussion of measuring bird populations by various [ 383] methods, we refer the reader to Kendeigh ( 1944). Here we need a brief summary of only the Forbes-Gross method, the strip census method used in the 1906-1909 and the 1956-1958 surveys. Forbes-Gross Strip Census The Forbes - Gross method of census- ing was described in essence by Forbes (1907:307), who stated that two ob- servers "were sent into the field under instructions to traverse the state in various directions, traveling always in straight lines and always thirty yards apart, and noting and recording the species, numbers, and exact situation of all birds flushed by them on a strip fifty yards in width, in- cluding also those crossing this strip within one hundred yards to their front. No at- tention is paid by them, for this purpose, to any (Jther birds." Forbes likened the census operation to "a gigantic sweep-net 150 feet wide and 300 feet deep, so drawn across the country day by day as to capture every bird which comes in its way; . . ." Certain details of the method were subsequently modified in the field, but the census techniques used during most of the survey by Gross and Ra\ in 1906-1909 were close to those described b\- Forbes & Gross (1921 :l-2). Our ultimate authority in determining the census technique actually used by the two observers in 1906-1909 has been the cor- respondence, journals, and original field notes of Dr. Alfred O. Gross. In open-field habitats (cornfields, soy- bean fields, and plowed ground), the two observers stayed 30 yards apart as they censused and counted all birds within or crossing a strip 50 yards in width in line with the observers and 100 yards to the front. In more dense habitats (orchards, forest, shrub-grown areas, and hayfields), the observers maintained a distance of 20 yards between them and censused a 30- yard strip. They traveled at the rate of about 40-50 minutes per mile. 3S4 Ii.iiNois Naturai, History Survhy Hli.i.htin \'nl. 28. Art. ,? Fit;. 1. — -Mfied O. Gross, right, and How- ard A. Ray as they appeared with winter field equipment at the time of the 1906-1909 bird censuses in Illinois. Usuall\ , censusing was started shortly after daybreak and continued, with inter- ruptions, until late afternoon. No censuses were made during periods of inclement weather, that is, when there was pre- cipitation or very strong wind. The dis- tance traveled in each habitat was paced, tallied with a hand counter, and recorded. Other pertinent information was re- corded: the date, time of day, locality, cloud condition, temperature, and num- ber of each species of bird in each habitat. Examples of the type of field notes taken were published bv Forbes iS: Gross (102.S:448-fJ). In censusing. Gross and Ray chose the general routes (Forbes d: Gross 1921, frontispiece) that they would travel, that is, between certain cities or other land- marks, but the censusing was random in the sense that the habitats were not chosen arbitrarily but were censused as they were encountered along the straight-line routes. Some of the areas censused by Gross and Rav are pictured as frontispieces and others as figs. 16, 20, 21, 29, and 30. Gross and Ray in winter field clothes and Gross on summer field trips are shown in figs. 1, 2, and 3. in 1956-1958, we censused in most of the counties that Gross and Ra\ had cen- sused, fig. 4, although we did not dupli- cate their routes exactly. After driving into a county, we deliberately chose a starting point in an area that seemed to represent the region. From the starting point, we walked a census strip along the perimeter of a square 1.5 to 2 miles on each side and returned ultimately to the starting point. Our rate of coverage, 45- 50 minutes per mile, was comparable to that of Gross and Ray. Though we de- liberateh chose each census area, we did October, 196.^ (jrahkr cS: (jrahkr: Hikd Poi'L i.ations in Illinois .^85 not arbitrarily select habitats, but censused all habitats as we encountered them along our straight-line routes. Thus, the habitat coverage in all our regular censusing was random. In the summer of 1958, we did supple- mentary' censusing in addition to our reg- ular censusing; we deliberatelj' chose and nois at all seasons of the year, but be- cause of the especially variable nature of bird populations in the migration seasons we decided to limit our censuses to the winter and summer seasons. In Illinois, spring migration of birds begins in Febru- ary and extends at least through the first week in June. For some species, fall mi- Fig. 3.—Alfred U. Gross, left, and helpers on a collecting trip near St. Joseph, Illinois, May, 1908. Gross and fellow students were studying distribution of various species of animals in Illinois. This particular field work was not part of the bird censuses of 1906, 1907, and 1909. censused additional acreage of certain habitats of limited area, such as marsh and orchard. We did this because we had encountered only a small acreage of these habitats along our regular census routes. Data from the supplementary censusing are included in tables with data from the regular censusing. In northern Illinois, we made censuses in the two northernmost tiers of counties except Cook County, In central Illinois, we conducted censuses through Vermilion, Champaign, Ford, Piatt, De Witt, Ma- con, Logan, Mason, Fulton, McDonough, and Hancock counties. In southern Illi- nois, we censused through ^Vabash, Ed- wards, Wayne, White, Gallatin, Hardin, Pope, Massac, Johnson, Pulaski, Alex- ander, Union, Jackson, Randolph, Perry, Jefi'erson, and Franklin counties. The original studies by Forbes & Gross included data on bird populations in mi- gration is under way by mid-July, and the migration lasts until December. Therefore, we conducted most of our summer censuses between early June and mid-July and our winter censuses between early December and March 1. Having access to Dr. Gross' original field notes, we were able to recalculate the 1906-1909 population densities for precisely the sea- sonal periods used in our censuses, thus insuring that the two sets of data were seasonally comparable. Because of the sea- sonal limitations and our recalculations mentioned above, our data for the Gross and Ra\ censuses do not correspond with data published by Forbes 5: Gross. Population data in this paper represent summer and winter censuses of the two surveys. The summer censuses were made during the following periods: in northern Illinois—June 30, Julv 1-3, 5-8, 1909; June 25-29, July 1-2, 1957; and June 386 Illinois Natlral History Survky Bulletin Vol. 28, Art. 3 30-[ulv 4. lulv lU-12, 14-15. 1958; in central Illinois—Mav 22-23. 27-29, 31, lulv 9-13. 15, 1907: June 22-26. 28-29. 1909; lune 18-19. 21-24. [ulv 8. 10. 12. 1957; and June 15. 17. 23-28. July 10. 1958; in southern Illinois — [une 4-8. 10-14. 17-21. 25-29. July 1. 1907; June Fig. 4.—Areas (indicated by black squares) in which the strip census method of estimating bird populations was used in 1956, 1957, 1958, and 1959. In most areas, censuses were made in both summer and winter, in a few areas in only one of these seasons. The boundaries be- tween the northern, central, and southern zones discussed in this paper are shown by heavy lines. S-11, 14-17, July 13-15, 1909; June 11-17, ful\ 8-10, 1957; and June 13-14, 18-21, July 8-9, 1958. The winter censuses were made during the following; periods: in northern Illinois —December 3, 6-8. 10. 1906; January 2-5, 8-11, 14-17, 1907; December 4-6, 1956; January 22-23, 1957 ; February 27, 1958; in central Illinois—December 11, 13, 17-18, 1906; January 21-25, 27, 29-30, February 1. 1907; December 14, 17, 1956; February 4-8, 1957; February 5_6. 12-14. 24-26. 1958; in southern Illi- nois—February 6-8. 9, 11-14. 18-21, 1907; December 27-28, 1956; January 8-13, 1957; and February 7-11, 1958. Forbes & Gross ( 1923:436) stated that the strip census method used in their studies limited them "to birds of more or less open country." Although reduced visibility in woodlands and dense shrub habitat undoubtedly affected the accuracy of the method, data for such habitats were gathered both in the earlier field work and in our own. However, in considering the value of the method, we were con- cerned primarily with open-field areas. In defining habitats, we placed primary em- phasis on the nature of the land cover, not on the land use. Thus, we classified a stand of alfalfa as a kind of hayfield even if it had been grazed. Ideally, all habitats censused should be represented by comparable large-size sam- ples, but in random strip censuses, such as were used in the recent and earlier studies, the observers covered different habitats approximately in proportion to the total acreage of each habitat in the areas censused. For certain habitats (such croplands as corn and small grain, for example) areas of several hundred acres were represented, while for some other habitats (for example, vegetable crops) only a few acres were represented. The data for habitats represented by only a few acres are probably not very signifi- cant; thus, there is a certain amount of waste in random strip censusing. In this paper, we have summarized virtually all the field data that were col- lected in the summer and winter seasons in both the 1906-1909 period and the 1956-1959 period regardless of sample size, but the question of what constitutes an adequate census area deserves further consideration in order to help the reader evaluate the data. The size of an adequate census area probably varies from habitat to habitat and season to season. In many habitats, open-field habitats especially, bird popula- tions are much more variable in winter than in summer, and winter census areas should presumably be larger than summer October, 196.^ Grabkr iS: Grabiir: Biro Poi'Ulations in Ili.inuis 387 areas. To obtain information on the re- lationship between the size of the census area in open fields and the measures of the bird population in such fields, we ex- amined data on open-field bird popula- tions from 427 summer strip counts in Fig. 5.—Bird population data for census areas (samples) of different sizes: (1) the per cent of the areas (samples) on which no birds were found, (2) the average numbers (average counts) of birds per acre, and (3) the maxi- mum numbers (maximum counts) of birds per acre. areas ranging in size from 0.3 acre to 80 acres and from 203 winter strip counts in areas ran^in^ in size from 0.2 acre to 74 acres. Three measures of bird popula- tions in these sample areas are presented in fi^. 5. The three measures were ( 1 ) the per cent of areas of difi'erent sizes \oid of birds, (2) the maximum counts of birds per acre in areas of different sizes, and (3) the average count of birds per acre for sample areas in each size class. In all strip census areas of 5 acres or less, about 49 per cent were void of birds in summer and 72 per cent in winter, fig. 5. For areas of 6-10 acres, the percentages were 19 in summer and 49 in winter, and, for areas of 1 1-20 acres, 7 in summer and 23 in winter. In summer, all census sam- ples of 19 acres or more contained at least 1 bird. In winter, 17 per cent of the areas of 21—30 acres had no birds, but all areas of 28 acres or more contained at least 1 bird. The curves representing the maximum counts of birds per acre in areas of differ- ent sizes, fig. 5, showed greater extremes of bird populations in winter than in summer and consequent!}' indicated the requirement of larger sample areas in winter. Maximum counts in plots of 5 acres or less were about 12 birds per acre in summer and 22 per acre in winter. As the size of the census plot was increased, the curve of maximum counts fell steeply (more steeply in summer than in winter), tended to level out, and attained a nearly constant level at about 25 acres in sum- mer and 50 acres in winter. The average counts of birds per acre in areas of dififerent sizes showed the sig- nificance of the size of the census area. In summer samples, the mean number of birds per acre fluctuated noticeably in sam- ples under 30 acres but was relatively constant in larger areas. In winter sam- ples, the mean fluctuated greatly in sam- ples under 50 acres but tended to level out for samples of larger size. These data suggest that, when the strip census method is used, the minimum size of census areas of open-field habitat should be not less than 30 acres in sum- mer and not less than 50 acres in winter. In discussing results of strip censuses, Forbes (1907:308-9, 1913:374-5) used the terms most iinportant , most abundant, and more abundant to designate those spe- cies of birds that together made up 85 per cent of a censused bird population, as, for example, the birds of a given habitat in summer. This percentage was selected ar- bitrarily. Because 85 per cent provides a good sample of the avifauna, we used this figure throughout the study in determin- ing the species designated as common in the various habitats discussed. (In deter- mining the common birds in the statewide population, we used 70 per cent, table 56; the number of species that together made up 85 per cent of the state population was too great to be included conveniently in a table.) Our data on Illinois acreages of the xarious habitats, fig. 6, have been deri\ed from one or more of four principal sources : ( 1 ) published records of the U.S. Bureau of the Census (1913, 1961), (2) 38S Illinois Natural History Survi-y Hullhtin Vol. 28, Art. .^ published records of the Illinois Coopera- tive Crop Reporting Service (Evving 1^50), (3) the published wetlands survey of the U. S. Fish and Wildlife Service (Shaw c<;c Fredine \^5b) , and (4) pub- lished records of the University of Illinois Agricultural Experiment Station (King 5: W^inters 1952). These sources were supplemented bv unpublished records of the 1006-1909 "and the 1956-1958 bird censuses. In discussing estimates of Illinois bird populations, we ha\e referred to northern, central, and southern zones of the state, fig. 4. P'or convenience, we based these zones on agricultural districts defined by the Illinois Cooperative Crop Reporting Service (Ewing 1959, map). In this study, the treatment of two such similar species as the eastern and the western meadowlarks, as well as the black- capped and the Carolina chickadees, offers a problem. Because in most instances we could not make specific determinations in these groups, we have usually lumped the data for the two species under one head- ing, for example, meadowlark (species?) or chickadee (species?). The basic quantitative data for this stud\ are presented in two types of tables, the first with emphasis on statistics (ex- ample: table 4), intended only to give the reader some impression of the inherent variability in the population data pre- sented, and the second with emphasis on avifauna (example: table 5), intended to Fig. 6.—Acreage of various bird habitats in Illinois from about 1800 through the years of the bird surveys reported here. Acreage data are principally from four sources: published records of the United States Bureau of the Census, published records of the Illinois Cooperative Crop Reporting Service (Ewing 1959), published wetlands survey of the U. S. Fish and Wild- life Service (Shaw & Fredine 1956), and published records of the University of Illinois Agri- cultural Experiment Station (King & Winters 1952). October, 196.^ Graker & Grabf.r: Bird Popui.atioxs ix Ii.i.ixois 389 provide data on the species of birds found in each habitat. Each table of the second ts'pe is arranged with the most numerous or the most frequently encountered species at the head of the list. Species of equal fre- quency are listed in phylogenetic sequence according to the American Ornithologists' Union (1957). Unidentified birds and birds identified only to genus, except those in Sturnella and Parus, are listed at the end of each of these tables. A few of these tables include species that appear to be out of habitat (for example, the Canada goose listed in table 54, the table for winter forests). The census method required that birds should be counted if they were in or over the census strips in front of the observers. In the example mentioned, a small flock of Canada geese crossed the census strip above some woodlands Ave were censusing. Thus, the ecological pic- ture presented in this and a few other tables is somewhat distorted. In the summer avifaunal tables for cer- tain habitats, we have designated some species of birds as being breeding species in those habitats. This designation means that the species were found nesting in the habitats either during the 1907-1909 or the 1957-1958 surveys. In this publication, we have adopted the common names of birds as presented by the American Ornithologists' Union (1957). A list of common and scientific names of all species encountered in the censuses ap- pears in table 55. Evaluation of Strip Census The strip census estimate of a bird population presumably has some relation- ship to the true population. A relatively constant relationship is all that we require of a census technique that we use to make comparisons between populations in dif- ferent habitats (or different time periods). The question remains as to how closely the strip census estimate approximates the true population of birds in a given habitat. Cooke (1915:2) felt that the strip census as reported by Forbes (1908) was so radi- cally different from the breeding-bird cen- sus that figures from the two censuses were not comparable. In order to determine how closely the strip census method reflected the true bird population, we ran both strip censuses and breeding-bird censuses on special study areas and compared the results. The breeding- bird census technique (Stone 1950:185-6) has been widely accepted as a reasonably accurate estimate of the true bird population of an area. Our comparison of the two types of census was conducted in June, 1959, on two study plots, each a 40-acre hayfield, located 1.5 miles apart near Sibley, Illi- nois. One field belonged to John Ames, the other to Herbert Brucker. The study plots were measured and staked off into squares of 1.6 acres each. In these areas, we made counts of singing males in the early morning (0600 to 0800 Central Standard Time) and located as many nests as possible. During the month, we determined as closely as possible the num- ber of birds breeding on each of the 40- acre tracts. We conducted breeding-bird counts usually every other day and on alternate days ran strip censuses across the study areas. In making the strip censuses in these fields, we followed the procedure used in censusing hayfields on our regular censuses. We chose hayfields for study because they support a fairly high bird population and a varied nesting fauna, and we were interested in qualitative as well as quan- titative comparison of data collected by the two methods. The two 40-acre fields differed in avi- faunal characteristics and other aspects. The Ames field was rolling and contained a higher percentage in sweet clover, while the Brucker field was flat and contained a higher percentage in red clover. The two fields harbored the same principal species of birds, though in different proportions, fig. 7. Our breeding-bird censuses indi- cated that the populations of birds in the Ames (area A) and the Brucker (area B) fields consisted of bobolinks, 28 and 24 per cent, respectively, of the total breeding- bird population ; dickcissels, 25 and 40 per cent; redwinged blackbirds, 21 and 10 per cent; grasshopper sparrows, 16 and 18 per cent; meadowlarks {Sturnella spp.), 8 per cent in each area ; and Henslow's sparrows, 2 and per cent. Our strip censuses showed that the populations of the two areas, A and B, consisted of bobo- links, 39 and 15 per cent, respectively; dickcissels, 17 and -I-5 per cent; redwinged 390 1 I.I.I Nois N.ATUR.M. History Survey Bum-etin Vol. 28. Art. .^ blackbirds, 16 ami 10 per cent; jjrass- hopper sparrows, 16 and 22 per cent; meadow-larks, 11 and 7 per cent; and Henslow's sparrows, 2 and per cent. Though the strip censuses did not show the population characteristics precisely, they clearly reflected the differences between the two Helds and provided a reason- abl\- accurate qualitative picture of the populations. Quantitatively, populations of the two fields differed markedlw as shown b>- both the breeding-bird and the strip censuses. AREA A rr (October, 1963 Grabur & (jraher: Bird Populations in Illinois 391 obtains a close approximation of the true population density, including both males and females of each species. In the strip 5+ 12+ 5+ 12+ BIRDS PER ACRE 3 4 5 6 7 "1—I—I—I— r AREA B AREA A I 2 3 4 5 6 7 8 BIRDS PER ACRE Fig. 8.—Populations of nongame birds in census areas of different sizes. The populations were estimated by strip censusing in two hayfields, areas A and B. Strip census areas (samples) were categorized by size (4 acres or less. 5 acres to 9 acres inclusive, 12 acres or more) ; each sample area represented 14 censuses conducted between June 4 and 21, 1959 (0600-1200 CST). The horizontal line through each open box represents the range of variation in the measure of the bird popula- tion; the vertical line represents the mean pop- ulation based on 14 censuses. Each open box represents one standard deviation each side of the mean, and each shaded box represents one standard error each side of the mean. census, on the other hand, some females (especially incubating females) are prob- ably overlooked, and, consequently, we might suppose the density indicated by a strip census to be less than the density in- dicated by a breeding-bird census. The fig- ures on density presented above do not bear out this supposition. To some extent the similarity in density figures is brought about by the behavior of the breeding males. There is a tendency for males of many species to approach the census strip and enter or cross it. This behavior may represent curiosity or aggressiveness to- ward an intruder; it has the effect of ex- aggerating the count of males per unit of area. By chance, this mechanism appears to compensate for the low count of fe- males during the incubation season. Variations in the strip census estimates of bird populations on the two special study areas are shown in fig. 8. The range of density values tended to decrease in strip census data as the size of the area censused increased, fig. 8. When the area censused was 4 acres or less, density values for the Ames area ranged from 2.9 to 7.1 birds per acre on dififerent census trips, while the values for areas of 12 acres or more ranged from 3.3 to 5.3. For the Brucker area, comparable values were 1.3 to 4.4 birds per acre (4 acres or less) and 2.1 to 3.7 birds per acre (12 acres or more). The data for population densities pre- sented above apply to nesting passerine birds only. Besides these passerines, there was a high population of pheasants in the Sibley area in which the Ames and Brucker fields were located. Ronald F. Labisky of the Illinois Natural History Survey, who has made intensive studies of the pheasant population in the Sibley area, reported that during the 1959 breed- ing season about 1.3 pheasant nests were established per acre of hayfield. Neither the breeding-bird census nor the strip cen- sus indicated a density of this magnitude for pheasants. The breeding-bird census indicated a pheasant population of 0.07 nest per acre on area A and 0.12 per acre on area B. The strip census indicated a population of 0.05 pheasant per acre on area A and 0.02 per acre on area B. Obviously, the strip census method is much less reliable for estimating pheasant populations than for estimating popula- tions of the more conspicuous passerines. Cooke (1915:2) pointed out that the number of birds per square mile in south- ern Illinois in June, 1907, as reported by Forbes (1908), was less than half the average for the national (breeding-bird) census; Forbes based his figures on strip censuses. The population data in our paper .^92 li.i.iNois Natural History Survhy Rui.i.ktin Vol. 28. Art. 3 ;iri' of \alut' priiiiaiil\ for comparisons within this stucl\ , and the rcadt-r should reco^ni/.e the specialized natvire of the data. The jireater variation of bird popula- tions in winter than in summer has al- ready been mentioned. It is difficult to de- termine to what decree the strip census estimates reflect the true winter popula- tion. In winter, birds are not so evenly distributed as in summer and they are less restricted to definite territories. These conditions decrease the accuracy of cen- susing, regardless of the method used. The j^reat variation in population data from four strip censuses in each of two areas in winter is shown in tables 1 and 2. Total population densities as indicated h\ the strip censuses varied from 10 to 107 birds per 100 acres in the cornfield and from 35 to 215 birds per 100 acres in the woodland. Only 1 of the 5 species recorded in the cornfield habitat was found on all four census trips, and only 2 species were found on at least three census trips. In the wood- land habitat, only 2 of 16 species of birds were found on all four census trips, only 4 species on at least three censuses, and 12 species on at least two censuses. Ad- Table 1.—Bird populations of a central Illinois cornfield in the winter of 1958—59 as de- termined by 40-acre strip censuses on four dates. Species Lapland longspur Mourning dove Horned lark Ring-necked pheasant Tree sparrow Total birds per 100 acres Number of species Birds Per 100 Acres December 18 December 19 December 30 January 13 5 10 89 18 107 2 3 11 3 12 71 12 95 3 Table 2.—Bird populations of a central Illinois woodland in the winter of 1958—59 as de- termined by 20-acre strip censuses on four dates. Species Downy woodpecker Re-z_ioci;i->ozaDQ:(r «IliJ- z -i iS ti;H>dzoo<^Q:>-z_io<333 UjOOlJ- z ^LJ^Q. ^3 ^ .J uj \^ \^ \ij d uj -5U.5< 5-5-i<(/50ZC)-5ll. T—I—I 1—I—I—I. 1. I. I—I—TT"oa.t->ozoDQ:cE>-z_ie> I I. 1. I. I. I. I; I. I I. I. 1^ UJOOUJ-zJ-z-ioa.i->ozoDtr(r>-zJo -3li.5<5-5-3u.5<5^-3 < PRECIPITATION »• /TEMPERATURE LONG TERM AVERAGE TEMPERATURE LONG TERM AVERAGE LONG TERM AVERAGE I I I I I I I I I I I I I I I I I ' LJ L_J I I I I—I I I I I I 2m(EQ:>2je)a;H>d2mQ:Q:>-2jtrJcLi->;ozcdQ^Q:>-z-i6 < iij i> 1956- 19 5 7- 1958- Fig. 10.—Temperature and precipitation deviations from the long-term averages in the northern, central, and southern zones of Illinois during and immediately preceding the years of the bird surveys of 1956-1958. 3% Illinois Natlrai. History Survkv Bulletin Vol. 28, Art. 3 was luit unusual otherwise. W'c do not know what effect low precipitation had on bird populations, but by l^)5b the precipi- tation level was coming back to normal, and we judj^e that the dryness of the earlier years probably had little effect on the bird populations surveyed. The census years of 195(>-U)5S showed a \ariable weather picture, ti^. 10, with temperature and precipitation fluctuating to about the same degree as in 1*^06-1909, The winter of 1956-57 in Illinois was relatively warm (except in January) and precipitation was normal ; the following spring and summer were about normal in temperature and normal or above normal in precipitation. No known weather con- ditions in this year would have had any special effect on bird populations in the state. The start of the winter of 1957-58 was mild, and precipitation continued to be normal, but February and March were \ery cold. The cold may have depressed populations of at least a few species of birds. The late part of the following spring was warm, but the summer was cool and wet. The summer conditions may have had an adverse effect on production of young birds, but the adult population, with which we were primarily concerned, was probablv not greatly affected. Our census data show that the state population of nesting birds was about the same in 1958 as in 1957 and tend to support the view that the early spring cold in 1958 had no general depressing effect on the state bird population. The years 1909, 1957. and 1958 in Illi- nois were probably similar to each other in terms of weather and its effect on bird populations. The 1907 bird population was depressed, and weather probably had a bearing on this depression. BIRD POPULATIONS IN SUMMER HABITATS Between the dates of May 22 and July 15, 14,447 acres were covered by strip censuses, 7,662 acres in 1907-1909 and 6,785 in 1957-1958. Acreages of the dif- ferent habitats censused in the two study periods combined ranged from 4,003 acres of corn to 1 acre of sugar cane. Because it is pointless to discuss bird populations in habitats represented by only small acreages, we have disregarded habitats represented by less than 50 acres. In table 3 are listed the summer habitats discussed in Table .1.—Acreages of habitats covered by summer strip censuses in the three zones of Illinois, 1907-1909 and 1957-1958. October, 1963 Graber & Gr.aber: Bird Populations in Illinois 397 this paper and the acreages covered by the strip censuses. Population data in both tables and text refer to supposedly adult birds. Juvenile birds were counted during the censuses, but, in order to eliminate a source of vari- ability, we did not include obviously ju- venile birds in population calculations. Cornfields (Summer) In terms of acreage, corn is the prin- cipal crop of Illinois. The cornfield habitat comprised almost 28 per cent (4,003 acres) of the land censused in the sum- mers of 1907-1909 and 1957-1958, table 3. From the data sources mentioned pre- viously, we calculated that corn acreage declined from about 10,400,000 acres in 1907 to 8,400,000 in 1957. Practices in corn culture have changed, but the char- acteristics of cornfields at the time of year the censuses were made have remained the same, fig. 11. At this season, the young plants in widely spaced rows (about 40 inches apart) usually varied in height from 3 or 4 inches to 2 feet, though some fields with plants over 3 feet in height were censused. The dominating feature of the cornfield habitat in early summer is bare ground. Quantitatively, corn is poor bird habi- tat, figs. 22-24. Mean numbers of birds per acre in corn for all census years in the three zones of the state in summers varied from 0.3 to 0.9, and the extreme variation for consecutive census years was 0.7 to 0.3 in 1957 and 1958,' table 4. Population densities were consistently higher in the northern zone than in other parts of the state. Also, they tended to be higher in the later than in the early census years, but the extreme annual variations preclude any precise conclusion on changes, between 1906 and 1958, in density of bird populations in cornfields of the state. Though there was no conclusive evidence of a general quantitative change in total bird population, the composition of the avifauna had altered. x\t least 60 species of birds were re- corded in summer cornfields in the two study periods combined ; this figure prob- ably reflects the large acreage covered more than it does the quality of the habi- tat. The complete list of species, with pop- ulation figures for each, is presented in table 5. Only 5 of the species (horned lark, grackle, house sparrow, mourning dove, and redwinged blackbird) were re- corded in this habitat in all years and all zones. The number of common species (those comprising 85 per cent of the population) in summer cornfields was higher in 1907 Table 4.—Statistical data on summer bird populations in Illinois cornfields as determined by strip censuses in the three zones. Data are (1) from all cornfields censused and (2) from sample areas (each 10 acres or more) in these fields. 398 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 Table 5.—^Summer avifauna in Illinois cornfields (birds per 100 acres) as determined by strip censuses in the three zones. Figures in parentheses indicate number of acres censused; + indicates less than 1 bird per 100 acres; * indicates breeding species in this habitat. NorniERN Zone Species *Horned lark Common grackle ,. House sparrow Mourning dove Reti winged black- bird . Meadowlark (species?) *Killdeer Brown-headed cowbird Starling Barn swallow Robin .,. Common crow *\'espei" sparrow Brown thrasher Yellow-shafted Hicker Eastern kingbird... Field sparrow American <;ol(l- finch Dickcissel Indigo bunting Mockingbird Red-headed woodpecker Tpland plover Chimney swift Lark sparrow Loggerhead shrike Blue jay Bobwhite Eastern bluebird . Sparrow hawk Cardinal Catbird Ring-necked pheasant Spotted sandpiper Purple martin . Bobolink ^'ellowthroat Turkey vulture Eastern phoebe Chipping sparrow Orchard oriole Greater prairie chicken Brewer's black- bird . . Traill's flycatcher Rufous-sided towhee 1909 i 1957 (351) (317) 10 13 + + 1 October, 1963 Graber & Graber: Bird Populations in Illinois 399 Table 5.—Continued 400 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 and 1909 in all zones censused than in 1957 and 1958, fig. 19. The pattern is one that can be observed over and over for the open-field habitats; that is, in these habitats the earlier avifauna of com- mon species was more varied than the re- cent. Related to this change is the fact that only three species (horned lark, red- winged blackbird, and barn swallow) comprised more of the cornfield popula- tion in 1957-1958 than in 1907-1909, while at least nine species were less prom- inent in the recent than the earlier corn- field avifauna, fig. 12. 70 60 SO In northern and central Illinois, by 1957 the horned lark had become the pre- dominant cornfield species, a change re- flected in the density figures, table 5. The change in the southern zone was less pronounced. The nesting avifauna for cornfields probably is composed principally of three species: the horned lark, vesper sparrow, and killdeer. Because so much of the summer avi- fauna of cornfields does not breed in this habitat, the list of species in table 5 must reflect marginal or edge habitat to some 40 30 q20 ID O CORNFIELDS NORTHERN ZONE- CENTRAL ZONE- SOUTHERN ZONE 1907 09 57 58 07 09 57 58 07 09 57 58 07 09 57 58 07 09 57 58 07 REDWINGED BARN CRACKLE BLACKBIRD HORNED LARK BARN SWALLOW MOURNING DOVE 09 57 58 CROW 10 \ \ 07 09 57 58 07 09 57 58 07 09 57 58 07 09 57 58 07 09 57 58 07 09 5758 FLICKER ROBIN RED-HEADED KINGBIRD MOCKINGBIRD BLUEBIRD WOODPECKER Fig. 12.—Relative abundance of common species of birds censused in cornfields of the northern, central, and southern zones of Illinois in the summers of 1907, 1909, 1957, and 1958. Only those species are included that showed changes in relative abundance (per cent of all birds counted in cornfields) between 1909 and 1957. October, 1963 Graber & Graber: Bird Populations in Illinois 401 extent. In all of the census years, regional differences were apparent. The cornfield avifauna of the central zone in summer was poorer both in number of species and in density of population than that of either the northern or the southern zone. Soybean Fields (Summer) Soybean acreage increased in Illinois from a few thousand acres before 1920 to more than 4,000,000 in 1954 (Ross & Case 1956:71); 777 acres of soybean fields were censused in 1957-1958. Soybeans were one of the crops charac- terized by considerable areas of bare ground at the start of the nesting season. In early June, at the start of censusing, the plants were less than 6 inches in height ; by the end of the summer census season they reached 12 inches or more. During this period, the areas of bare earth were gradually closed in by the plants, and the habitat probably became less de- sirable for the open-field bird species that predominate in bare-ground habitats. Soybean fields were about the poorest of bird habitats, both in number of species and number of individual birds, figs. 22- 24. The average number of birds per acre of soybeans for the various years and zones in summer ranged from 0.1 to 0.9. Pop- ulations tended to be lowest in the south- ern zone, tables 6 and 7. In central Illi- nois, the zone for which we had the larg- est samples, mean densities were 0.9 bird per acre in 1957 and 0.5 in 1958, table 6. Maximum variation of bird populations in any one zone in consecutive census years was from 0.1 to 0.5 bird per acre, in south- ern Illinois. At least 28 species of birds were iden- tified in soybean fields in the summers of 1957 and 1958, table 7. Though no spe- cies was recorded in this habitat in both years in all regions, the horned lark, grackle, redwinged blackbird, mourning dove, and goldfinch were reported with high frequency. Probably only the horned lark and the vesper sparrow nested regu- larly in this habitat ; the horned lark was the predominant species. Plowed Fields (Summer) In early summer, relatively little Illi- nois land can be classed as plowed fields. Only 335 acres of this habitat were cen- sused in summers of the two study pe- riods. Despite the total lack of cover, plowed fields had avifaunal associations about comparable to those of cornfields and soybean fields. Bird population densities in plowed fields in summer varied from 0.6 to 1.4 birds per acre (57 birds per 100 acres in 1907 to 140 birds per 100 acres in 1957, table 8). In the southern zone, the only one in which large areas of plowed fields were censused, these fields held popula- tions of about 0.6 bird per acre in 1957- 1958, indicating relatively poor habitat. Twenty-nine species of birds were iden- tified in plowed fields in summer, table 8; this fauna was slightly richer in species than that found in urban residential areas. Probably a very low percentage of the species found in plowed fields actually nested in this habitat. Probable nesting species were the horned lark and the kill- deer. Only in the southern zone was the cen- sus area of plowed fields large enough to warrant avifaunal comparisons between the two census periods. In this zone, 10 species of birds comprised the common summer avifauna of plowed fields censused in 1907 and only 7 species in 1958, fig. 19. In plowed fields, as in soybean fields and cornfields, the horned lark was the pre- dominant summer species, figs. 12 and 13 and table 7. Oat Fields (Summer) The acreage of oats in Illinois de- creased from about 4,300,000 acres in 1907 to 2,800,000 acres in 1957. The reduction was accompanied by an increase in soybean production. In all census years, oat production was higher in the northern two-thirds of the state than in the south- ern third. In summers of the two study periods, 1,319 acres of oats fields were censused, table 3, only about 300 acres in 1957- 1958. Only 10 acres were censused in the southern zone in 1957-1958. At the time of the summer censuses, the oat plants had attained nearly full growth (12-18 inches) and were headed out. The fields were green in the early part of the census and ripened before the end of July. Most fields had scattered weeds that produced 402 Illinois N.atural History Survey Bulletin Vol. 28. Art. 3 Table 6.—Statistical data on summer bird populations in Illinois soybean fields as deter- mined by strip censuses in the three zones. Data are (1) from all soybean fields censused and (2) from sample areas (each 10 acres or more) in these fields. October, 1963 Graber & Graber: Bird Populations in Illinois 403 Table 8.—Summer avifauna in Illinois plowed fields (birds per 100 acres) as determined by strip censuses in two zones. Figures in parentheses indicate numbers of acres censused. Species Horned lark Brown-headed cowbird._.. Mourning dove Killdeer Lark sparrow Robin Common grackle Eastern kingbird .__. House sparrow Redwinged blackbird Eastern meadowlark Field sparrow Brown thrasher Indigo bunting Eastern bluebird Red-tailed hawk Red-headed woodpecker.. Common crow Bewick's wren Mockingbird Loggerhead shrike Chimney swift Dickcissel Yellow-shafted flicker Red-shouldered hawk Bobwhite Upland plover Black-billed cuckoo Downy woodpecker - Total birds per 100 acres Number of species . Central Zone Southern Zone 1957 (25) 92 8 12 16 UO 6 1907 (68) 1 1 1 57 19 1909 (66) 15 35 21 130 15 1957 (83) 13 4 7 17 62 13 1958 (56) 14 9 7 56 11 Q?^n 404 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 an aspect more like that of ha\ fields than other grain crops, and the avifauna showed some roscmhlance to the nesting avifauna in havfields. For all census years and zones, mean densities of summer bird populations in oats varied from 0.5 to 2.7 birds per acre; the greatest variation in consecutive years Table 9.—Statistical data on summer bird populations in Illinois oat fields as determined by strip censuses in the three zones. Data are (1) from all oat fields censused and (2) from sample areas (each 10 acres or more) in these fields. The data from sample areas are for breeding species only. October, 1963 Graber &: Graber: Bird Populations in Illinois 405 was from 2.7 birds per acre in 1957 to 1.3 in 1958, in the northern zone, table 9. Densities were higher in the northern than in other zones and in the later than in the earlv series of censuses. In 1907-1909, the density of bird populations in oat fields ranged from 0.5 to 1.0 bird per acre and averaged 0.7, about comparable to density of the populations in cornfields. In 1957 and 1958, the population in oat Table 10.—Summer avifauna in Illinois oat fields (birds per 100 acres) as determined by strip censuses in the three zones. Figures in parentheses indicate numbers of acres censused; + indicates less than I bird per 100 acres; * indicates breeding species in this habitat. 406 Illinois N.^tural History Survey Bulletix Vol. 28, Art. 3 fields ranged from 1.0 to 2.7 birds per Population densities of breeding species acre and averaged 1.5, a density well showed minimum and maximum figures above that for cornfields. for 1907-1909 of 0.1 bird per acre (in the Table 11.—Statistical data on summer bird populations in Illinois wheat fields as determined by strip censuses in two zones. Data are (1) from all wheat fields censused and (2) from sample areas (each 10 acres or more) in these fields. The data from sample areas are for breeding species only. October, 1963 Graber & Graber: Bird Populations in Illinois 407 northern zone) and 0.6 per acre (in the southern zone) ; for 1957-1958, these fig- ures were 0.3 bird per acre (in the central zone) and 2.0 birds per acre (in the north- ern zone), table 9. Because census samples were small for the later years, we must be cautious in drawing conclusions, but the data indi- cate that summer bird population densi- ties increased in oat fields between 1909 and 1957. The change in population den- sities of birds in this habitat can probably be attributed to population changes in a few species, particularly the redwinged blackbird and the bobolink, fig. 14. At least 44 species of birds were re- corded in oat fields in summers of the two census periods combined, table 10, but only 2, the house sparrow and the east- ern meadowlark, were found in all zones and in all years. The number of species recorded was considerably greater in 1907-1909 than in 1957-1958, probably because of the greater acreage covered in the early census period. Wheat Fields (Summer) The acreage of Illinois land planted to wheat has varied greatly since 1909. From about 2,000,000 acres in the period 1890- Table 12.—Summer avifauna in Illinois wheat fields (birds per 100 acres) as determined by strip censuses in two zones. Figures in parentheses indicate numbers of acres censused ; -|- indicates less than 1 bird per 100 acres; * indicates breedinrf species in this habitat. Species House sparrow *Redwinged blackbird *Dickcissel Mourning dove Common grackle Indigo bunting *MeadowIark (species?).- Field sparrow 1. Bobwhite Barn swallow Horned lark Starling *Grasshopper sparrow Purple martin *Brown-headed cowbird— Rough-winged swallow.- Chimney swift Red-headed woodpecker.. Yellowthroat Song sparrow Greater prairie chicken... Yellow-billed cuckoo Sparrow hawk Brown thrasher Robin Upland plover Cliff swallow Common crow Mockingbird Orchard oriole... Cardinal. Catbird Lark sparrow Unidentified bird Total birds per 100 acres Number of species Central Zone Southern- Zone 1907 (28) 257 4 7 18 7 11 4 334 11 1909 (141) 14 11 7 3 11 16 7 408 Illinois Natural History Survey Bulletin V^ol. 28, Art. 3 1905, wheat land increased to over 4,000,- 000 acres in 1919 and then decreased to an average of 1,500,000 per year in the period 1940-1950 (Ross & Case 1956: 70). This crop in Illinois is grown mainly in the southern and central zones, and vir- tually all of the 773 acres of wheat fields censused for birds represented these zones. At the time censusing started each year, the wheat plants were 1.5-2 feet tall, green, and headed out. The plants ripened during June and July and were cut in July and August. Ripe wheat would ap- pear to be an inhospitably warm habitat for birds. Wheat fields were found to be a rela- tively poor habitat for birds in summer, Hgs. 22-24, supporting populations slight- ly higher than those in the crops of corn and beans. Basic statistical data for years in which the largest acreages were cen- sused are presented in table 11. For these years the number of birds per acre in wheat fields ranged from 0.6 to 0.8, in southern Illinois. Breeding species usu- ally comprised one-fourth to one-half of the total population in wheat fields and varied from 0.1 to 0.3 bird per acre. The data, though meager, suggest that the den- sity of wheat field populations was about the same in the central and southern zones and in the two census periods. At least 33 species of birds were iden- tified in wheat fields in summer, table 12. No species was reported in all years in both the central and southern zones, but the mourning dove was a common species in all years in the southern zone. In both zones, the eastern meadowlarlc and the dickcissel were recorded with very high frequency. These species, the redwinged blackbird, and the grasshopper sparrow nested in wheat fields at least in the early part of the summer, though wheat is prob- ably poor nesting habitat for any species. In the central zone, the dickcissel used this habitat more in 1957-1958 than in 1907-1909, table 12; in the southern zone, the redwinged blackbird was the predom- inant species on wheat land at the time of the second survey, fig. 15. Pastures (Summer) The censuses indicated a marked reduc- tion in pasture acreage between 1909 and 1957, particularly in the central and Fig. 16.—Pastuieland with trees. The acreage of savanna-like habitats of this kind was greatly reduced between 1909 and 1957. The reduction contributed importantly to a loss of species variety in the avifauna of many parts of Illinois. Photograph taken near Ogden, Illinois, May 28, 1907, by Alfred O. Gross. October, 1963 Graber & Gr.aber: Bird Popul.ations in Illinois 409 southern zones. In summers of the two study periods, 2,087 acres of pasture were censused for birds, only one-fourth of this total in 1957-1958. We estimated that the area of nonwoodland pasture declined from about 6,100,000 acres in 1907 to 2,000,000 in 1957. The pastures referred to in this report were virtually all stands of bluegrass {Poa pratensis) , some with scattered low in the central zone. Bird population den- sities were highest in the central and northern zones and tended to be higher in the second census period than in the first. A clearer picture of the pasture popu- lations and their variations is obtained if only known breeding species are consid- ered, tables 13 and 14 and fig. 17. The average number of breeding birds per acre of pasture in the various censuses ranged Table 13.—Statistical data on summer bird populations in Illinois pastures as determined by strip censuses in the three zones. Data are (1) from all pastures censused and (2) from sample areas (each 5 acres or more) in these fields. The data from sample areas are for breeding species only. 410 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 Table 14.—Summer avifauna in Illinois pastures (birds per 100 acres) as determined by strip censuses in the three zones. Figures in parentheses indicate numbers of acres censused; + indicates less than 1 bird per 100 acres; * indicates breeding species in this habitat. Species Northern Zone 1909 (193) 1957 (147) •Meadowlark (species?) 14 35 House sparrow 27 ! 9 Common grackle 28 *Red\vinged black- bird 11 29 •Field sparrow . 6 3 *Brown-headed cowbird 23 6 Barn swallow 7 9 Yellow-shafted flicker 17 3 Robin 12 1 •Grasshopper sparrow 3 7 Starling. 13 •Savannah spar- row 6 24 •Dickcissel 3 1 Brown thrasher... 3 1 Mourning dove 2 4 American gold- finch ... .... 2 6 •Bobolink... 5 11 •Bobwhite 1 •Horned lark 6 Eastern king- bird 5 7 Eastern bluebird... 1 3 Blue jay 2 1 Red-headed woodpecker . 3 Common crow. 6 Orchard oriole + •Killdeer 1 5 Chimney swift 2 *Vesper sparrow 3 7 Indigo bunting . . 1 •Song sparrow ... 1 - 4 Mockingbird ^'ellnw-billed cuckoo 1 1 •Lark sparrow •Upland plover ... 3 2 House wren Baltimore oriole + 1 Cardinal Sparrow hawk + Catbird 3 Bank swallow 4 Loggerhead shr'ke ... . j 1 Chipping sparrow 3 Yellowthroat . | -|- Purpl? martin i Bewick's wren 1958 (132) 39 11 16 52 2 4 11 3 1 5 23 17 1 7 17 1 4 2 Central Zone Southern Zone 1907 (287) 19 31 15 1 5 2 2 10 4 4 1 1 7 2 1 + + 1909 October, 1963 Grabhr ^ Graber: Bird Populations in Illinois 411 studies and in all zones of the state. Sev- enteen species of birds were believed to breed in pastures, table 14. The meadowlarks appeared to increase their population densities between 1909 and 1957, particularly in the northern and Table 14.—Continued Species Northern Zone 1909 (193) Tree swallow .„ Green heron Turkey vulture Great crested fly- catcher Eastern phoebe^. + Chickadee (species?) Tufted titmouse Red-tailed hawk Rough-winged swallow Bell's vireo- ___ Rufous-sided towhee Carolina wren Spotted sandpiper Common night- hawk Red-bellied wood- pecker Eastern wood pewee Red-eyed vireo Yellow-breasted chat . Black-crowned night heron 1 *Greater prairie chicken 1 Ring-necked I pheasant 1 Belted kingfisher j White-breasted nuthatch Brewer's black- bird Marsh hawk ! -j- American wood- \ cock Black-billed cuckoo Hairy woodpecker Downy wood- pecker Summer tanager - *Bachman's spar- | row I .— Hawk (species?) -. I - . Unidentified bird -. 3 Total birds per [ WO acres . ! 224 Number of species i 42 1957 (147) 1958 (132) Central Zone 1907 (287) 1909 (155) + + + + 210 32 228 25 + 1 U6 35 1957 (54) 1958 (118) 222 36 29-f 28 223 28 Southern" Zone 1507 (601) + 2 + + + + + + + + + 2 128 49 1909 (281) + + 1 4- + 4- + 157 42 195 7 (72) 1958 (48) 151 26 210 15 412 Illinois Natural History Survey Bulletin' Vol. 28, Art. 3 NORTHERN ZONE o'-l-t-^ Birds per acre Fig. 17.—Populations of breeding species of birds censusetl in Illinois pastures in 1907—1909 and 1957-1958. The vertical line through each black rectangle indicates the mean, each open box one standard deviation on either side of the mean, each black rectangle two standard errors on either side of the mean, and each set of arrows the range. central Illinois zones, as field sparrows did in the central and southern zones, table 14 and fig. 18. Other species showing in- creases both in relative rank and actual density were the redwinged blackbird (northern zone) and the savannah spar- row (northern zone), fig. 18 and table 14. Ungrazed Grasslands (Summer) The acreage of ungrazed grasslands in Illinois is relativelv small. We encoun- tered the habitat principally along railroad rights-of-way and road edges. We esti- mated that the area of this habitat de- clined from about 330,000 acres in 1907 to 218,000 in 1957. Excluding roadside grass, 165 acres of this habitat were cov- ered during summers of the two census periods in the nothern and southern zones of Illinois. As a bird habitat, the ungrazed grass- lands were closely allied to pastures and fallow fields; woody plants were almost completely lacking in the ungrazed grass- lands. The cover of grasses and forbs in the ungrazed grasslands was taller (about 2-3 feet tall) than that in pastures and it was more dense. Summer bird populations in ungrazed grasslands (excluding roadside grass) were comparable to those in other grass- land habitats, with densities varying from approximately 1.2 to 3.9 birds per acre ( 119 to 386 birds per 100 acres, table 15) ; the densities in ungrazed grasslands were higher in the northern zone than in the southern zone. At least 29 species of birds were iden- tified in ungrazed grasslands in summer, table 15. Species common in this habitat were the redwinged blackbird and the eastern and western meadowlarks. 50^ !^40_ Q. 10 _ 0_ PASTURELAND NORTHERN ZONE -— CENTRAL ZONE SOUTHERN ZONE 0709 57 58 0709 57 58 07 09 5758 0709 57 58 07 09 57 58 07 09 57 58 07 09 57 58 07 09 5758 MEAOOWLARK REDWINGED SAVANNAH STARLING FIELD BARN GOLDFINCH HOUSE BLACKBIRD SPARROW SPARROW SWALLOW SPARROW Fig. 18.—Relative abundance of common species of birds censused in pastureland of the northern, central, and southern zones of Illinois in the summers of 1907, 1909, 1957, and 1958. Only those species are included that showed changes in relative abundance (per cent of all birds counted in pastureland) between 1909 and 1957. October, 1963 Graber & Graber: Bird Populations in Illinois 413 Table 15.—Summer avifauna in Illinois ungrazed grasslands (birds per 100 acres) as de- termined by strip censuses in two zones (open stands only; no roadside or edge grass areas included in this table). Figures in parentheses indicate numbers of acres censused ; * indicates breeding species in this habitat. Species *Meadowlark (species?)... *Redwinged blackbird Mourning dove Horned lark Common grackie *Bobolink Barn swallow Swamp sparrow Field sparrow American goldfinch.... Song sparrow "*Grasshopper sparrow Brown-headed cowbird.... House sparrow *Dickcissel Robin *Bobwhite Bl ue j ay Common crow Yellow-shafted flicker Indigo bunting *Savannah sparrow Common egret American redstart Red-headed woodpecker.. Starling Killdeer.. Bank swallow Short-billed marsh wren.. Unidentified bird Total birds per 100 acres Number of species Northern Zone 1909 (15) 47 88 7 20 54 27 20 7 284 9 1957 (10) 19 9 38 19 9 19 38 178 9 1958 (49) 66 41 98 113 10 4 2 4 4 10 2 2 2 2 10 386 17 Southern Zone 1907 (33) 67 36 12 139 1957 (20) 115 30 15 25 15 5 230 10 1958 (38) 37 13 13 21 13 5 119 11 Fallow Fields (Summer) As we define the habitat, fallow fields are fields that have been cultivated and then left unused for a year or longer. Such fields support a variety of weeds and grasses that form a fairly dense cover to a height of 2-4 feet. Small shrubs may be found scattered in the older fallow fields, but woody plants are not a dominant fea- ture of the habitat. As a bird habitat, fal- low land probabh' bears closest resem- blance to pasture or ungrazed grassland. Agricultural census figures and our own census data indicate that the area of fallow land in Illinois declined from about 1,- 500,000 acres in 1909 to 1,000,000 in 1957. Logically, acreage of fallow lands should diminish as a swelling human pop- ulation increases the demand for culti- vated land. In Illinois, largest acreages of this habitat were found in the southern zone ; smallest acreages were in the in- tensively cultivated area of east central Illinois. In the study periods, 682 acres of fallow land were censused, table 3. Population levels of birds in fallow fields in the southern zone did not change greatly in the half century after 1909, table 16. As bird habitat, the fallow land censused was rich in numbers and species, being about comparable to pastureland. The numbers of birds per acre for all cen- sus summers in the southern zone ranged from 1.3 to 1.7. Among the breeding spe- 414 Illinois N.\tur.\i. History Survey Bulletin Vol. 28, Art. 3 Table 16.—Statistical data on summer bird populations in Illinois fallow fields as de- termined by strip censuses in the southern zone. Data are (1) from all fallow fields censused in this zone and (2) from sample areas (each 10 acres or more) in these fields. The data from sample areas are for breeding species only. October, 1963 Graber & Graber: Bird Populations in Illinois 415 Table 17.—Summer avifauna in Illinois fallow fields (birds per 100 acres) as determined by strip censuses in the three zones. Figures in parentheses indicate numbers of acres censused ; * indicates breeding species in this habitat. Species *Mourning dove *Redvvinged blackbird *Meadowlark (species ?)- *Dickcissel *Horned lark Common grackle *Field sparrow House sparrow American goldfinch _— . Indigo bunting Eastern kingbird Brown thrasher *Lark sparrow *Yellowthroat *Grasshopper sparrow *Brown-headed cowbird... Barn swallow Cardinal .._ Orchard oriole Eastern bluebird Yellow-headed blackbird *Bobwhite Yellow-shafted flicker Mockingbird Starling Upland plover Blue jay *Bewick's wren Chimney swift Ring-necked pheasant Red-headed woodpecker.. Rough-winged swallow.- Savannah sparrow Common crow Robin - Sparrow hawk Purple martin Loggerhead shrike Yeilow-breasted chat KiUdeer Yellow-billed cuckoo Common nighthawk Downy woodpecker Great crested flycatcher... Cliff swallow Carolina wren Rufous-sided towhee *Bachman's sparrow Chipping sparrow Hawk (species?) Unidentified bird Total birds per 100 acres Number of species Northern Zone 1957 (26) 11 42 27 11 11 160 11 1958 (22) 41 41 41 81 18 13 13 4 4 2-7 12 Central Zone 1957 (25) 56 60 12 116 20 16 12 336 13 Southern Zone 1907 (138) 1909 (181) 6 9 26 11 1 6 1 2 1 1 3 1 1 1 1 1 1 1 1 1 1 1 128 31 11 5 46 9 4 149 32 1957 (153) 38 22 16 12 10 12 6 10 1 1 4 152 20 416 Illinois N.atural History Survey Bulletin- Vol. 28. Art. 3 clover. The present account concerns mixed hay. During the two study periods, 1,212 acres of this habitat were censused in summer, less than 400 acres of it in 1057-1958, table 3. The strip census data and published ag- ricultural records indicate that the total acreage of mixed hay in Illinois (over 2,- 500,000 acres) was about the same in 1907-1909 as in 1957-1958; the mixed hay acreage declined in the north and in- creased in the south. Mixed hay usually forms a dense cover 2 to 3 feet in height at maturity and is generally composed of various mixtures of grasses (timothy, brome, and wild grasses) and legumes ( red clover, sweet clover, and alfalfa). As a bird habitat, mixed hay was fairly rich in species and verv rich in numbers of birds, f^gs. 22-24 and tables 18 and 19. At least 14 species of birds were found to nest in this habitat, table 19. As fig. 5 shows, field-to-field variation of bird pop- ulations in this habitat was high. Average densities of birds (all species) per acre in mixed hayfields in summer ranged from 1.1 to 8.2 birds per acre; the numbers of birds per acre in successive census years in one zone ranged from 1.8 in 1957 to 8.2 in 1958, in the central zone, table 18. Such high variability and the relatively small samples in the later census period make conclusions tenuous, but bird popu- lations in northern zone haytields ap- peared to be conspicuouslv higher in 1957- 1958 than in 1909. Average densities of breeding-bird popu- lations in mixed hayfields ranged from 0.5 to 7.1 birds per acre, table 18. These pop- ulations were usually highest in northern Illinois, and almost invariably they were higher in the later than in the early years. The numbers of breeding birds per acre in 1907-1909 ranged from 0.5 to 1.4; in 1957-1958 the range was from 0.8 to 7.1, table 18. This apparent increase in population density between 1909 and 1958 may be attributable to a few species. Of the 57 or more species found in summer hayfields, table 19, only the eastern meadowlark was reported in all census years and in all zones, though the redwinged blackbird, dickcissel, and grasshopper sparrow were reported with very high frequency. Com- mon hayfleld birds are listed in tables 20, 21, and 22. In the hayfield fauna, the meadowlarks were found to be increas- ingly important from northern to southern latitudes in 1907-1909, as well as in re- cent census years. In northern Illinois, Table 18.—Statistical data on summer bird populations in mixed hayfields of Illinois as determined by strip censuses in the three zones. Data are (1) from all mixed hayfields censused and (2) from sample areas (each 4 acres or more) in these fields. The data from sample areas are for breeding species only. October, 1963 Graber tS: Graber: Bird Populations in Illinois 417 Table 19—Summer avifauna in mixed hayfields of Illinois (birds per 100 acres) as de- termined by strip censuses in the three zones. Figures in parentheses indicate numbers of acres censused; * indicates breeding species in this habitat. Species *Redwinged blackbird *Meadowlark (species?) *Dickcissel *Bobolink *Grasshopper sparrow House sparrow Common grackle Mourning dove *Savannah spar- row Barn swallow *Bobwhite Yellow-shafted flicker *Brown-headed cowbird American goldfinch Robin Brown thrasher . Starling *Up!and plover Brewer's black- bird Common crow Eastern kingbird Swamp sparrow. _ Chimney swift ... *HensIow's spar- row Song sparrow Killdeer Horned lark .. .. *Short-billed marsh wren Yellowthroat *Vesper sparrow .. Field sparrow Common night- hawk . Ruby-throated hummingbird Purple martin Bachman's spar- row Black tern Red-headed wood- pecker Indigo bunting Sparrow hawk .... *Ring-necked pheasant Northern Zone 1909 (175) 29 25 53 9 45 1957 (91) 230 25 10 75 1 13 7 1958 (30) 220 50 60 67 17 47 7 3 20 10 7 7 17 3 13 10 3 Central Zone 1907 (60) 1909 (65) 13 15 15 2 13 18 53 50 18 35 11 6 15 5 3 3 15 1957 (55) 31 33 74 2 14 2 1958 (24) 249 69 212 37 122 77 Southern Zone 4 4 16 12 1907 (330) 22 57 23 4 12 6 5 1 + 5 + 2 3 1909 (204) 12 59 21 1 4 + 1957 (33) 1958 (26) 61 6 121 74 35 12 16 418 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 Table 19.—Continued Species Northern Zone 1909 (175) Traill's flycatcher. Orchard oriole | -— Eastern bluebird I 1 Loggerhead shrike Red-shouldered hawk *Greater prairie chicken \ ellow-bilied cuckoo Blue jay Mockingbird Catbird Lark sparrow Green heron Turkey vulture . Down}' wood- pecker _[ .... Great crested I flycatcher Eastern phoebe Cardinal Melospiza (species?) I .... Unidentified bird [ 3 Total birds per 100 acres 229 Number of species 27 1957 (91) 2 10 404 23 1958 (30) 27 622 23 Central Zone 1907 (60) 114 16 1909 (65) 244 20 1957 (55) 177 10 1958 (24) 822 13 Southern Zone 1907 (330) 1 + + I + + 160 30 1909 (204) 1 + + + + + 146 29 1957 (33) 112 7 1958 (26) 310 13 meadowlarks appeared to be relatively less common in the hayfield fauna in 1957 than in 1909, tables 20 and 21, despite the re- cent spread of the western meadowlark into the northern half of the state. The red\vin:round cover was bluej^rass. A typical orchard censused in 1907 is shown in fig. 20. In the two study periods combined, 172 acres of orchard were censused, table 3, most of them in southern Illinois. Orchards were shown to be excellent bird habitat, supporting high populations and a varied avifauna. In southern Illi- nois, summer bird populations in orchards were higher than in any other habitat ex- cept red clover and residential areas, fig. 24. Census data for the years with the largest acreages censused, 1909 and 1958, indicated populations of 3.9 and 4.7 birds per acre in the southern zone and 2.0 birds per acre in the northern zone (391, 475, and 199 birds per 100 acres, table 34). At least 45 species of birds were identi- fied in orchards, table 34, virtually all be- ing potential nesters in this habitat. The mourning dove, field sparrow, robin, and indigo bunting were reported in both northern and southern Illinois in the sum- mers for which census figures are availa- ble. In addition, in the southern zone, the house sparrow, cardinal, eastern meadow- lark, mockingbird, and yellowthroat were listed in all census vears. Comparisons of bird populations of 1907-1909 with those of 1957-1958 are difficult to make because of the marked \ear-to-year \ariations and the small sizes of the samples, but there appears to be no real difiference in total density of the or- chard bird populations of the two periods. Population changes in some species oc- curred, however, table 35. An increase in population of the redwinged blackbird was apparent in this as in other habitats, and an increase in the barn swallow popu- lation in orchards was indicated. An ob-; servable decline occurred in orchard popu-j lations of a few species, particularly th^ orchard oriole, tufted titmouse, hous wren, yellow-shafted flicker, Carolinsj chickadee, red-headed woodpecker, crestec flycatcher, and eastern kingbird, tables 34 and 35. Forests (Summer) About 40 per cent of the land area of Illinois was originally forested, but three- fourths of this area has been cleared (King & Winters 1952:20-1). We estimated that there were about 3,500,000 acres of forest in Illinois in 1907-1909 and nearlv 4,000,000 acres in 1957-1958. Most of the forest lies in southern Illinois. Table 35.—Common birds (species making up approximately 85 per cent of birds counted in strip censuses) in orchards in the southern zone of Illinois, summers, 1907—1909 and 1957— 1958; + indicates approximately 0.5 per cent. 1907-1909 1957-1958 Species House sparrow Field sparrow Mourning dove , Orchard oriole Common grackle Rol)in Catbird Blue jay Brown thrasher Kastern meadowlaric - Mockingbird Tufted titmouse Bewick's wren Cardinal Yellow-shafted flicker House wren Indigo bunting „ Yellow warbler Total per cent Number of species Per Cent 16 10+ 9 7+ 5-f 5 4+ 4 3 3 3 2+ 2+ 2+ 2 2 2 1+ 85 18 Species House sparrow Common grackle Mourning dove Starling Redwinged blackbird Field sparrow Cardinal ^ Barn swallow Indigo bunting Brown thrasher Eastern meadowlaric American goldfinch Bobwhite - . DIckcissel Total per cent Number of specie- Per Cent 16 13 11 85 14 October, 1963 Graber & Graber: Bird Populations in Illinois 431 Table 36.—Statistical data on summer bird populations in Illinois forests with understory as determined by strip censuses in the three zones. Data are (1) from all such forests censused and (2) from sample areas (each 1 acre or more) in these forests. 432 Illinois Natural History Survky Bulletin Vol. 28, Art. 3 Table 38.—Summer avifauna in Illinois forests (birds per 100 acres) as determined by strip censuses in the three zones (forests with and forests without understory were included in the counts). Figures in parentheses indicate numbers of acres censused; data from the northern and central zones in 1907 and 1909 are too meager to be valid and they have not been included in this table. All stands included in this table were mature, natural deciduous forest typical of Illinois. Dense thickets of young saplings were not classified as forest. Most of the species of birds listed in this table are known to nest in forest. October, 1963 Graber &: Graber: Bird Populations ix Illinois 43: Table 38.—Continued Species Barred owl Yellow-throated vireo ._._ Rose-breasted grosbeak- Scarlet tanager Eastern kingbird Orchard oriole ._... Warbling vireo Paruia warbler Lark sparrow Red-shouldered hawk Ring-necked pheasant Piieated woodpecker Yellow warbler Great horned owl Hooded warbler Baltimore oriole Great blue heron.. Common egret Green heron Turkey vulture Cooper's hawk Black-billed cuckoo Whip-poor-will Chimney swift Eastern phoebe Black and white warbler Louisiana waterthrush House sparrow Meadowlark (species?).. Blue grosbeak Dendrocopos ( species ?).. Hawk (species?) Caprimitlffus (species?).. Unidentified bird Total birds per WO acres Number of species Northern Zone 1957 (79) 9 222 37 1958 (98) 10 115 30 Central Zone 1957 (97) 1 11 218 38 1958 (117) Southern Zone 1907 (20) 16 256 38 5 350 24 1909 4.U Illinois Natural History Survey Buli-etin Vol. 28, Art. 3 Table 39.—Common birds (species making up approximately 85 per cent of birds counted in strip censuses) in woodlands with understory in Illinois, summers, 1957 and 1958. Northern Zone Central Zone Southern Zone Species Per Cent Species Per Cent Species Per Cent Chickadee (species?) Brown-headed cowbird Red-eyed vireo Cardinal Ovenbird Dfndrocopos (species?) American goldfinch Kastern wood pewee Indigo bunting Robin _ _ Starling— Red-tailed hawk Common crow Blue jay - Ruby-throated humming bird -.. Red-headed woodpecker House wren Catbird Blue-gray gnatcatcher.... Total per cent. Number of species 15 11 10 84 19 Cardinal Tufted titmouse Blue jay.- Downy woodpecker Chickadee (species ?).... . Eastern wood pewee Indigo bunting Mourning dove Robin — Catbird American redstart Brown-headed cowbird Great crested flycatcher Brown thrasher Red-bellied woodpecker Red-headed woodpecker Common crow Red-eyed vireo -.... Common grackle Hairy woodpecker Rufous-sided towhee Field sparrow Total per cent Number of species 14 11 6 S 5 4 4 4 3 3 3 3 3 3 3 2 2 2 2 1 1 1 S5 22 Cardinal Tufted titmouse Indigo bunting Acadian flycatcher Chickadee (species?) Carolina wren Kentucky warbler Blue-gray gnatcatcher... Red-eyed vireo White-eyed vireo . Rufous-sided towhee Brown-headed cowbird Eastern wood pewee Wood thrush Field sparrow Common crow Red-bellied woodpecker Summer tanager Worm-eating warbler Downy woodpecker . Mourning dove ._.. Cerulean warbler ... Yellow-throated vireo American goldfinch Blue jay American redstart .. Yellow-breasted chat Total per cent— .. Number of species -. 10 9 7 7 5 4 4 4 3 3 3 3 2 2 2 2 2 2 2 85 27 Table 40.—Common birds (species making up approximately 85 per cent of birds counted) in woodlands in the northern zone of Illinois, summers, 1957 and 1958. Woodlands With Understory Woodlands Without Understory Species Per Cent Chickadee ( species ?) Brown-headed cowbird Red -eyed vireo Cardinal _ Ovenbird Dcndrocopos (species ? ) American goldfinch Eastern wood pewee Indigo bunting . Robin Starling Red-tailed hawk _ Common crow Blue jay Ruby-throated hummingbird. Red-headed woodpecker House wren C atbi rd Blue-gray gnatcatcher.. Total per cent Number of species 15 11 10 g 7 5 5 4 3 3 2 2 2 2 1 1 1 1 1 84- 19 Species Common grackle Yellow-shafted flicker ... Blue jay Eastern bluebird Eastern wood pewee.. Red-headed woodpecker Redwinged blackbird American goldfinch Robin .. Common crow Starling Per Cent Total per cent Number of species 48 6 5 4 4 82 11 October, 1963 Graber & Graber: Bird Populations in Illinois 435 of forest censused in 1907-1909 was so small that the fig;ures derived may not be representative. At least 80 species representing 27 fami- lies of birds were identified in forest (both with and without understory), table 38. The cardinal, indigo bunting, blue jay, red-ej^ed vireo, wood pewee, and downy woodpecker were recorded in all summers and zones in which censuses were made. Other species for which the frequency of occurrence was very high were tufted tit- mouse, crow, crested flycatcher, towhee, mourning dove, and wood thrush. Indica- tions of increases in forest populations be- tween 1909 and 1957 were shown by the chickadees, blue-gray gnatcatcher, Ken- tucky warbler, and white-eyed vireo, table Fig. 21.—Forest with understory in southern Illinois censused in the summer of 1907. Such species as the summer tanager and wood thrush were recorded here. The photograph was taken east of Shetlerville, Hardin County, June 29, 1907, bv Alfred O. Gross. 436 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 38. Species that showed some consistent marked population reduction between 1*^09 and 1957 were blue jay, crested fly- catcher, wood thrush, brown thrasher, red- headed woodpecker, and yellow-shafted flicker. Lists of common forest species (species comprising 85 per cent of the populations in forests with understory) in the three zones in the summers of 1957 and 1958 are presented in table 39. The forest avi- fauna was progressively more varied from northern to southern latitudes. The num- bers of common species in the southern zone were about the same in 1907-1909 as in 1957-1958 in spite of the much larger area covered in the later censuses. Though there were no consistent differ- ences in density of bird populations be- tween woods with understory and those lacking understory, tables 36 and 37, there were qualitative differences, table 40. The avifauna of the forest without understory was less varied, and the species composi- tion was different in that such shrub-nest- ing and ground-nesting species as the car- dinal and ovenbird were scarce or lacking in forest without understory. Urban Residential Areas (Summer) The spread of urban residential areas began long before the first strip censuses reported here, but the acreage of land oc- cupied by human residences and lawns in- creased greatly after 1909. We have esti- mated that acreage of this habitat climbed from about 350,000 acres in 1907 to 820,- 000 in 1957. Only a small acreage of urban residen- tial areas was censused in the summers of 1907-1909. In 1958, we made summer censuses in the residential areas of several Table 41.—Summer avifauna in Illinois urban residential areas (birds per 100 acres) as determined by strip censuses in the three zones in 1958. Figures in parentheses indicate num- bers of acres censused. Most of the species listed are known to nest in this habitat. Species October, 1963 Graber & Graber: Bird Populations in Illinois 437 Table 42.—Common birds (species making up approximately 85 per cent of birds counted in strip censuses) in urban residential areas in the three zones of Illinois, summer, 1958. Northern Zone 438 Illinois Natural History Survey Bulletin Vol. 28, Art. BIROS PER ACRE 10 20 30 40 50 60 70 80 90 100 1 I I I ' I I I I 1 1 — MARSH SHRUB RESIDENTIAL A MIXED HAY A-_ SWEET CLOVER A UNGRA2ED GRASS A 1957 A 1958 ^ RED CL j^ A FALLOW ^ PASTURE ^ ALFALFA A ORCHARD OATS NORTHERN ZONE SUMMER FORESTA ^ CORN ^ SOYBEANS 10 20 30 4.0 50 6 70 8.0 9 100 I I I I 1 I I \ I I 1 BIRDS PER ACRE Fig. 22.—Densities of summer bird popula- tions in a number of habitats in the northern zone of Illinois as determined by strip censuses in 1957 and 1958. The point of each triangle indicates the mean number of birds per acre for all fields of the habitat censused in the year and zone specified. and zones) combined and include all birds seen and all acreaji;es censused. Number of Birds.—Of the 17 major summer habitats censused in the various years and zones, the row crops of corn and soybeans consistently supported the lowest bird populations; the\' had an aver- aj^e density of about 0.6 bird per acre. Plowed ground, oats, and wheat were also poor habitats for birds; their average pop- ulations were 0.8, 0.8, and 0.9 bird per acre, respectively. Bird populations in oat fields showed marked increase between the 1909 and the 1957 censuses; populations were consistently low (0.6 bird per acre) in the early censuses, but relatively high in later years (1.7 birds per acre), primarily because of increases in the Icteridae. Pop- ulations in wheat fields showed no such change. Wheat, which is harvested earlier than oats, is a less attractive habitat. Summer bird populations in grassland> and hay crops were variable, but usually conspicuoush higher than in the bare- Held, row-crop, and small-grain habitats. For these, the average bird population levels (birds per acre) for all censuses were as follows: fallow fields, 1.6; pas- ture, 1.7; ungrazed grassland, 2.2; mixed hay, 2.2; alfalfa, 2.5; red clover, 2.8; and sweet clover, 4.1. Forests (all types) in summer sup- ported populations of 2.4 birds per acre, about comparable to grasslands and hay habitats. Ihe remaining habitats, shrub- grown areas (3.5 birds per acre), orchard (4.0), marsh (7.9), urban residential (8.9), and edge shrub (22.3), supported denser populations of birds. In several habitats (plowed fields and row crops), the population of breeding species constituted only a relatively small part of the total population of these habi- tats in summer. Populations of breeding species were 0.2 bird per acre in corn and BIRDS PER ACRE 1.0 2.0 3 40 50 60 70 8.0 9.0 100 October, 1963 Graber & Graber: Bird Populations in Illinois 439 BIRDS PER ACRE 1.0 2.0 30 40 5.0 6.0 7.0 8.0 90 10 RESIDENTIAL A A ORCHARD RED CLOVER 2i SHRUB A^ FOREST A MIXED HAY A ALFALFA ^5"^ PASTURE A 1957 A 1958 UNGRAZED GRASS ^ FALLOW ^ WHEAT SOUTHERN ZONE SUMMER A ^ CORN ^ PLOWED ^ SOYBEANS I 2 30 40 5 6 70 8 9 10 I 1 1 I I I I I I I i__ BIRDS PER ACRE Fig. 24.— Densities of summer bird popula- tions in a number of habitats in the southern zone of Illinois as determined by strip censuses in 1957 and 1958. The point of each triangle indicates the mean number of birds per acre for all fields of the habitat censused in the year and zone specified. 0.4 bird per acre in plowed fields and soy- beans. In wheat, the populations of breeding species were 0.3 bird per acre. In oats, the level of the breeding population changed markedly from 1907-1909 (0.2 bird per acre) to 1957-1958 (1.1 birds per acre), and the average figure for the two census periods (0.4 bird per acre) has little mean- ing. The grassland and related habitats had varied populations of breeding birds; 0.8 bird per acre in fallow fields and pastures and 1.5 birds per acre in ungrazed grass. The population levels in pasture, at least, showed some increase from 1907 to 1909 (from 0.5 to 0.7 bird per acre) to 1957 to 1959 (from 0.9 to 1.4 birds per acre). Ungrazed grasslands had notably higher summer populations than other grass hab- itats and higher proportions of breeding birds relative to the total populations. Breeding-bird populations in hay crops were less varied tjualitatively but higher quantitatively than those in grassland. The numbers of birds per acre were 1.5 in mixed hay, 1.7 in alfalfa, 1.9 in red clover, and 2.8 in sweet clover (small sample). Breeding-bird populations in hayfields increased markedly during the half century following 1909. Virtually all of the species recorded in summer for forests and urban residential areas were potential breeders or nesters in these habitats. Populations of breeding species were, for forests, 2.4 birds per acre; orchards, 3.3; shrub-grown areas, 3.5; marshes, 5.5; and urban residential areas, 8.9. Number of Species.—The censused habitats that supported the greatest num- bers of birds in summer did not necessarily support the most varied avifaunas. How- ever, the row-crop and bare-field habitats (corn, soybeans, and plowed ground) that had low populations in terms of birds per acre were also low in numbers of species. In these habitats, only the horned lark oc- curred regularly as a nesting species, ta- bles 5 and 7. In small-grain fields, the total nesting avifauna, which included at least 10 spe- cies, was much more varied than that in row crops, tables 10 and 12. Even more varied was the avifauna of grasslands and fallow fields, which sup- ported at least 20 species of breeding birds, tables 14, 15, and 17. The avifauna in hay crops was less varied than that in grasslands. The 14 species of birds breed- ing in hayfields were grassland species that tolerated or even preferred the tall, dense hay cover, tables 19, 24, 26, and 28. The marshland avifauna in northern Illinois was rich in number of species, and at least 18 of the 41 or more species in the marsh habitats in summer were nesters, table 30 ; this habitat was similar to grass- lands and fallow fields in number of breeding species, but the marshland avi- fauna was much more specialized. The woody habitats (shrub areas, or- chard, and forest) were the richest of the summer habitats in numbers of species, tables 31, 34, and 38. About 40 of the 74 or more species of birds found in shrub- grown land probably nested in this habi- tat ; in orchards, 37 of the 45 or more spe- 440 Illinois Natural History Survky Bulletin Vol. 28, Art. 3 cies recorded were probably nesters; and virtually all of the 80 or more species found in forest probably nested there. Residential areas, thoujjh a woody habi- tat, had a much more restricted summer avifauna, with 28 species, table 41, prob- ably all of them nesting in this habitat. In two habitats that were roughly simi- lar, the population density tended to be higher in the habitat in which the avi- fauna-habitat relationship was more spe- cialized and the avifauna was less varied. For example, residential areas, which had a more specialized avifauna-habitat rela- tionship and a less varied avifauna than forests, had consistently higher popula- tion densities. Statewide Summer Populations A factor that must be considered in evaluating a particular habitat for birds is its total acreage. For instance, though ungrazed grasslands support a relatively high population of birds per unit of area, this high population density has little ef- fect on the state population because of the very limited acreage of the habitat. Extrapolating from the crop acreages presented by the Illinois Co-operative Crop Reporting Service (Ewing 1959), the U. S. Bureau of the Census (1913, 1961), and our census data, we can roughly estimate the total number of birds in a given habitat and also the total num- ber of birds in the state for the summers of 1909, 1957, and 1958 (no data for northern zone in 1907). Illinois has a total land area of about 35,800,000 acres. Ironically, the largest single habitat type in the state (row crops, principally corn and soybeans) is also one of the poorest of the bird habitats. If the censuses show the true distribution of birds in the various habitats of the state at given times, then in the summer of 1909 there were about 6,376,000 birds in the row crops (10,483,000 acres) : corn (10,- 173,000 acres) and garden vegetables (310,000). By 1Q57, the land in corn (all types) had been reduced to about 8,280,- 000 acres, but another row crop, soybeans, had come into prominence and amounted to 4,979,000 acres, while garden vegetables accounted for only 70,300 acres. The total area of row-crop habitat was thus in- creased by nearly 3,000,000 acres over the 1909 acreage. In 1057, the total popula- tion of birds in this habitat was estimated to be 8,170,000, an increase of about 1,- 790,000 over the 1909 population. The importance of the row-crop and plowed-field habitats as feeding grounds for birds is difficult to evaluate. The ulti- mate appraisal should be in terms of spe- cies survival, which is closely associated with nesting opportunity ; in this frame of reference, the row crops have relatively little importance to the total avifauna. The expansion of row crops at the expense of other habitats represents a loss in both variety and numbers of birds. Small grain crops in Illinois have de- creased in acreage since 1909, when there were about 4,235,000 acres of oats (plus rye) and the summer population in this habitat was estimated to be about 2,955,- 000 birds. In 1957, there were 2,990,000 acres of oats (plus rye) in Illinois; de- spite the decrease in acreage, the bird pop- ulation in the habitat was estimated to be even higher than in 1909 (5,552,000) be- cause of an increase in population density in the habitat, particularly among the Icteridae in the northern half of the state. The acreage of wheat (plus barlev) de- creased from 2,250,000 in 1909 to 1,960,- 000 in 1957; the bird population in this habitat also decreased (1909: 1,494,000; 1957: 1,121,000). By our estimate, the area of ungrazed grassland in Illinois decreased from about 331,000 acres in 1909 to 218,000 in 1957, and the state bird populations in this habi- tat from 612,000 birds in 1909 to 464,000 in 1957. We estimated that fallow fields in the state occupied 1,496,000 acres in 1909 and 1,034,000 in 1957; our estimates of the populations in this habitat were 2,244,000 birds in 1909 and 1,663,000 in 1957. In 1909, there were in Illinois about 6,085,000 acres of nonwoodland sod pas- ture that contained a summer population estimated at 11,650,000 birds. In 1957, though over 2,000,000 acres of hay and other crops were used for pasture, sod pastureland amounted to only 1,965,000 acres ; the bird population in this habitat was estimated to be 4,139,000, 7,500,000 below the 1909 population. Not all of the reduction represented breeding birds; if we consider breeding species only, the esti- October, 1963 Graber & Graber: Bird Populations in Illinois 441 mated number of birds in Illinois pastures decreased from 4,800,000 in 1909 to 2,- 160,000 in 1957. Coincidental with the loss in acreage of grassland, there was an increased use of cultivated hay plants for pasture in Illi- nois, and, in recent years, increased acre- age of soil improvement (soil bank) hay. Thus, while the acreage of hay plants for harvest declined from 3,349,000 acres in 1909 to 2,459,000 acres in 1957, the total acreage of hay plants for all purposes was 5,254,000 acres in 1957, an increase of 1,905,000 acres over the 1909 acreage. In the same period, there was some change in the types of hay produced. Alfalfa had a negligible acreage (18,000 acres) in 1909, but it had become a leading hav crop (1,424,000 acres) by 1957. Timothy, on the other hand, was planted on 1,870,000 acres in 1909, while in 1957 there was very little acreage of pure timothy. In 1909, timothy and mixed hay had about the same qualitative-quantitative avifaunal characteristics, and for final tabulation we lumped the census data for these crops. In all summer hay crops combined, the total summer population was estimated to be 6,834,000 birds in 1909 and 12,930,000 in 1957. For the most part, the increase represented increased acreage, for popula- tion densities in this habitat were similar over most of the state in 1909 and 1957. To some extent, the increase in hayfield acreage replaced the lost acreage in pas- tureland, but the gain in the hayfield bird population compensated for the loss in the pastureland population only in numbers of birds, not in variety of birds. The amount of prairie (nonwood, non- shrub) marshland in Illinois decreased from about 558,000 acres in 1909 to about 60,000 acres in 1957. The estimated total bird population for this rich habitat was 4,140,000 in 1909 and 293,000 in 1957. These figures represent an estimated loss of 3,847,000 birds in the population and, even more important, a loss in faunal va- riety. The marsh avifauna is highly varied and highly specialized, and most of the marsh species cannot survive in another habitat. Based on our census data, the acreage of shrub-grown areas in 1909 (469,000 acres) was close to that in 1957 (507,000 acres). Despite the limited acreage, esti- mated summer bird populations were high in shrub-grown habitat: 1,993,000 birds in 1909 and 1,892,000 in 1957. In 1909, there were about 301,000 acres of Illinois orchards with an estimated sum- mer population of 1,422,000 birds. By 1957, when orchards had been reduced to about 31,000 acres, the estimated summer population (108,000 birds) in this habitat was negligible by comparison with the 1909 level. Though most species of or- chard birds can survive in other habitats (shrub-grown areas and forest or wood- lands), the loss is still regrettable. Prob- ably much of this high-density habitat, which supported a varied avifauna, was replaced by poor-habitat crops, such as soybeans. Forest or woodland acreage was prob- ably greater in 1957 than in 1909, when there were, by our estimates, about 3,459,- 000 acres with a statewide summer popu- lation of 14,149,000 birds. In 1957, forests covered 3,996,000 acres, but the statewide population of birds (9,886,000) was estimated to be less (by 4,261,000) than in 1909, because population densities in forests tended to be lower in the later years. Acreages for urban residential areas in Illinois are not available for 1909, but on the basis of the urban (human) popula- tion and acreage data for urban areas in later years, we estimate that there were about 350,000 acres of urban areas in Illi- nois in 1909. If the 1909 and 1957 bird population densities in this habitat were comparable to the 1958 level, when cen- suses were made, then the estimated sum- mer population in 1909 was about 3,269,- 000 birds. By 1960, the acreage of urban areas had increased to about 820,000 acres and the bird population to about 7,657,- 000. Commercial sections of urban areas have much smaller bird populations than residential sections. Virtually no native species are found in commercial areas ; the avifauna of these areas consists almost en- tirely of the three introduced species (house sparrow, starling, and rock dove). Urban residential areas represent a modi- fied forest habitat that can be an important reservoir for several species of native birds. For all of the habitats mentioned, our estimates of the total statewide popula- 442 Illinois Natural History Survbv Hli.lrtin Vol. 28, Art. 3 tions of adult birds in summer were 57,- 138,000 in \909 and 53.875,000 in 1^)57. These data accounted for 33,368,000 acres in 1000 and 32.200,000 in 1957, leaving some of the acreage for the state unac- counted for: about 2.400,000 acres in 1000 and 3.505,000 in 1057. In 1057, about 1,280.000 acres of land (excluding urban areas) were covered by the con- crete, asphalt, or gravel of the state or federal highways and 14,000 additional acres were covered by railroad tracks and ties. Some road surfaces (especially gravel) may be of some value to birds, hut. if we appraise in terms of species survival, road surfaces must be consid- ered a void in the statewide acreage of bird habitats. Even after the acreage of these areas was included, there were still about 2,202,000 acres unaccounted for in 1957. Some of this acreage undoubtedly represented good bird habitats, such as cemeteries, grassy roadsides, and sod air- fields, while part of it must have repre- sented poor habitats, such as extraurban factories, other rural buildings, and paved airport runways. Included among the high-density habitats, as yet unaccounted for, were edge shrubs (estimated acreage in 1057: 86,000; estimated bird popula- tion in 1957: 1,918,000) and hedgerows (estimated acreage in 1957: 13,000; esti- mated bird population in 1957: 172,000) ; we lack comparative data on these habitats for 1909. If our estimates are reasonably close to the actual numbers, there was little change in the total number of summer bird residents in the state between 1909 and 1957. If the acreage unaccounted for in 1909 and 1957 had harbored bird pop- ulations comparable to those in the acre- age accounted for, then Illinois would have had state bird populations of about 61,333,000 birds (mean densitv for state, 1.71 birds per acre) in 1909 and 59,778,- 000 birds (mean density for state, 1.67 birds per acre) in 1957. One possible ex- planation of the closeness of the 1009 and the 1957 populations is that the state land area has a saturation population level of about 60,000,000 birds in summer and that this saturation level had been reached at least as early as 1909. There is a limit to the mass of protoplasm that can be supported on a given land area. This mass of protoplasm could be expressed in terms of numbers of birds (and other animals) per unit area. It seems unlikely that the number of birds on a land area the size of Illinois would remain constant from \'ear to year through the decades, even if a saturation level had been reached. Too man\ interdependent factors are involved —including the varied nature of the avi- fauna itself. To obtain data on year-to-year varia- tions in the statewide bird population, we estimated the 1958 population, as well as the 1909 and 1957 populations; no data are available for the northern zone in 1907, and we did not estimate the state population for that year. In the summer of 1958, we estimated, there were 60,244,- 000 birds on 32,806,000 acres of Illinois land (1.84 birds per acre), or, for the total acreage in the state, about 65,586,COO birds, about 5,600,000 more than in 1957. The 1957 and 1958 summer popula- tions showed that the number of birds in the state may vary appreciably from one year to another even though the acreages of each habitat remain about the same. Appreciable variations in bird populations are to be expected. The population in one year depends on productivity in the pre- vious year and on survival of birds in mi- gration and on the wintering grounds. Because weather is variable, productivity (therefore population) may vary greatly from year to year, as well as from habitat to habitat and from zone to zone. For 1957 and 1958, our estimates of bird populations in Illinois cornfields were, re- spectively, 5,705,000 and 5,397,000 birds. In the same period, the number of birds in oat fields changed drasticallv (1957: 5,552,000; 1958: 3,276,000). While the bird population in oat fields decreased, the population in wheat fields increased from 1957 to 1958 (from 1,121,000 to 2,459,000). Both of these changes may have represented the same phenomenon, that is, a habitat shift by birds from one type of grain field to another. Mean population densities varied some- what from zone to zone. The northern zone consistently had the highest average density in summer. Mean densities in the summer (June) of 1909 were 2.0 birds per acre for the northern zone (2.5 in 1957, 2.4 in 1958); 1.4 for the central October, 1963 Graber & Graber: Biro Populations in Illinois 443 zone (1.4 in 1957, 1.7 in 1958) ; and 1.7 for the southern zone (1.4 in 1957, 1.7 in 1958). To some extent this variation re- flects the lack of uniformity in distribu- tion of such high-densit\' habitats as urban residential areas, marsh, and forest. The relatively low mean density for the south- ern zone is surprising in view of the large acreage of forest in this zone. The gross figures for the statewide summer population of birds include many species of birds, all of which have fluctuat- ing populations. Population increases in one species might cancel decreases in an- other species. It is pointless to speculate further on the meaning of the gross changes until we have considered the in- dividual species in more detail. One generalization can be made here: that among the habitats considered—some primarily natural (prairie, forest, marsh) and some cultivated (corn and soybeans) — the 1909 summer bird populations tended to be higher in the natural habi- tats and the 1957 populations higher in the cultivated habitats. BIRD POPULATIONS IN WINTER HABITATS Bird populations in winter are much more variable than in summer, and com- parison of results of the two sets of cen- suses as an index to long-term changes in the avifauna is somewhat tenuous. During the winter season (December 1 -February 15), 10,180 acres of Illinois land were censused, 5,299 acres in 1906- 07 and 4,881 in 1956-57 and 1957-58. The acreages of each habitat covered in different regions and different winters are shown in table 43. The habitats in order of descending acreage were corn, pasture, small grain stubble, wheat, hayrield, forest, plowed ground, soybean stubble, fallow land, shrub-grown area, orchard, and marsh. The acreages of orchard and marsh were so small that we did not cal- culate the bird populations in them. 1 he bird populations for the other types of habitat are discussed below. A comparison of bird population densities in various habitats is shown in figs. 25—27. Cornfields (Winter) The methods of corn harvesting have changed considerably since the first winter survey by Gross and Ray. Hand-picked fields, which comprised most of the corn- field acreage in the winter of 1906-07, were characterized by the tall cover of the standing stalks and by little grain left in the fields. Fields in which the stalks were cut offered little cover (except where there were shocks) and in this respect bore some resemblance to modern harvested fields. However, none of the early cornfield types was strictly comparable as a winter habi- tat to the cornfields of todav. Mechanical Table 43.—Acreages of habitats covered in winter strip censuses in the three zones of Illinois, 1906-07, 1956-57, and 1957-58. 444 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 BIROS PER ACRE 1.0 2.0 3.0 150 160 170 SHRUB A FOREST A FALLOW A CORN STUBBLE A SMALL GRAIN STUBBLE A HAYFIELD A PASTURE A PLOWED A WHEAT A SOYBEAN STUBBLE 10 20 30 I 1 1 1 ^f A 1956-57 NORTHERN ZONE WINTER 150 160 170 BIRDS PER ACRE Fig. 25.— Densities of winter bird popula- tions in a number of habitats in the northern zone of Illinois as determined by strip cen- suses in 1956—57. The point of each triangle indicates the mean number of birds per acre for all fields of the habitat censused in the year and zone specified. picking of the grain leaves broken-over stalks and scattered grain throughout the fields. Modern cornfields in winter offer relatively little concealing or protective cover, but a considerable amount of food for some species of birds. Of 2,896 acres of cornfields censused for birds in winter (all years), 1,184 acres represented fields that had been hand picked ( 1906-07), 254 acres were of fields from which the stalks had been cut and removed (1906-07), 93 acres had had the corn cut and shocked (1906-07), and 1 ,365 acres were of mechanicalh' picked cornfields (1956-57 and 1957-58), tables 44 and 45. In the various types of cornfields, in all census years, winter bird populations tended to be most dense and most varied in the southern zone of the state, least dense and least varied in the northern zone, tables 44 and 45. Two types of cornfield habitats, hand-picked (standing cornstalk) fields in 1906-07 and me- chanically picked fields in 1956-57 and 1957-58, were especially important be- cause each type occupied most of the corn acreage in its period. BIRDS PER ACRE 1.0 2.0 3.0 4.0 8.0 9.0 10.0 I I I I I yi I I I SHRUB ^— ^ FOREST CORN STUBBLE -A HAYFIELD PLOWED A 1956-57 1957-58 ^ SMALL GRAIN STUBBLE A_2^ SOYBEAN STUBBLE ^ ^^^^°^ CENTRAL ZONE / PASTURE WINTER A WHEAT 10 20 3.0 4 80 90 10.0 I J 1 1 1 // 1 1 1 BIRDS PER ACRE Fig. 26.—Densities of winter bird popula- tions in a number of habitats in the central zone of Illinois as determined by strip censuses in 1956-57 and 1957-58. The point of each triangle indicates the mean number of birds per acre for all fields of the habitat censused in the year and zone specified. BIRDS PER ACRE 1.0 2.0 3.0 40 14.0 15.0 16.0 170 18.0 -//- SHRUB ^ A_^ FALLOW A FOREST -A SOYBEAN STUBBLE PASTURE SMALL GRAIN STUBBLE ^ CORN STUBBLE ^ HAYFIELD SOUTHERN ZONE PLOWED WINTER ^ WHEAT 2 A 1956-57 1958-59 1.0 2.0 30 40 14.0 15.0 16.0 170 18.0 I 1 1 1 1 // I I I I I BIRDS PER ACRE Fig. 27.— Densities of winter bird popula- tions in a number of habitats in the southern zone of Illinois as determined by strip censuses in 1956-57 and 1957-58. The point of each triangle indicates the mean number of birds per acre for all fields of the habitat censused in the year and zone specified. The term s/truh in figs. 25-27 includes both shrub-grown areas and edge shrub. October, 1963 Graber & Graber: Bird Populations in Illinois 445 Quantitative!}', bird populations in the two types were similar. Bird populations in hand-picked cornfields in the winter of 1906-07 (most of the censuses were in January) were 0.2 bird per acre (22 birds per 100 acres) in the northern zone, 1.4 birds per acre (138 birds per 100 acres) in the central zone, and 2.0 birds per acre (203 birds per 100 acres) in the southern zone, table 44. Bird populations in me- chanically picked cornfields in the winter of 1956-57 (most of the censuses were in January) were 0.5 bird per acre (50 birds per 100 acres) in the northern zone, 2.1 birds per acre (207 birds per 100 acres) in the central zone, and 1.9 birds per acre (188 birds per 100 acres) in the southern zone, table 45. Qualitatively, there were some impor- tant differences between the two periods with respect to the winter bird popu- lations of cornfields. The winter avifauna of hand-picked fields (1906-07) was com- posed more of species that we usually think of as shrub or forest-edge inhabitants, while the winter avifauna of mechanically picked fields contained more prairie or open-field species, such as the horned lark and Lapland longspur. The taller cover of hand-picked fields (1906-07) was of Table 44.—Winter avifauna in Illinois cornfields of different types (birds per 100 acres) as deter mined by strip censuses in the three zones in 1906—07. In the first type, the ears have been pickei and the stalks left standing; in the second, the stalks have been cut and shocked; in the third, th< stalks have been cut and removed, leaving only short stubble. Figures in parentheses indicate num bars of acres censused; + indicates less than 1 bird per 100 acres. Northern Zone Central Zone Species Ears Picked (602) Common crow — . Slate-colored junco Tree sparrow Meadowlark (species ?)- Cardinal Mourning dove Chickadee (species?) House sparrow Bobwhite American goldfinch Yellow-shafted flicker Song sparrow Horned lark Sparrow hawk Downy woodpecker Eastern bluebird Carolina wren White-throated sparrow.. Blue jay Red-bellied woodpecker... Tufted titmouse Turkey vulture. Robin Fox sparrow Rough-legged hawk Red-headed woodpecker.. Mockingbird Loggerhead shrike White-breasted nuthatch Hawk (species?) Total birds per 100 acres Number of spec'es 1 + 7 + 9 + 4- + 22 10 Stalks Cut and Shocked (42) Stalks Cut and Re- moved (90) Ears Picked (360 125 9 1 + + 1 + + + + 138 10 Stalks Cut and Shocked (49) 22 38 4 16 Stalks Cut and Re- moved (107) Southern 2Jone 2 92 11 1 2 7 24 6 Ears Picked (222) Stalks Cut and Shocked (2) 4 51 2 59 3 36 3 1 16 1 8 3 1 + 1 4 1 -I- 1 1 1 + + + + 203 26 Stalks Cut anc Re- moved (57) 10 47 40 5 7 14 2 152 15 44t. Illinois Natural History Survey Bullktin Vol. 28, Art. 3 IK) value to these open-field liinls, and they were surely favored by the habitat changes that came with mechanical harvestinjz- In iqoe)-(l7. the cut fields, which should pre- sumably have been jjood habitat for the lark, had poor populations of these species. The winter data, like the data for sum- mer, indicate that the lark population in- creased helds, particularly those in harvested ha\ tields, were probably forajjinj;. Wheat, jjenerally a very poor bird habitat, had relativelv high populations of doves. Han- son & Kossack (1957:178; 1963:92) have pointed out the importance of wheat in the niournini: dove diet. In 1907-1909, rye was a much-favored habitat in south- ern Illinois—probablv even more than wheat—but the sample was too small to give a valid density figure. Oat fields were the poorest of the dove habitats in all zones of the state. Open space appears to be an important characteristic of all of the dove habitats with high population density ; the difiference between dove popu- lations in urban areas (high density) and those in forests (low density) may in part reflect this characteristic. The density figures presented above rep- resent mostly, but not solely, adult popu- lations. While we did not include iden- tifiable juveniles in the calculations, some well-grown birds of the year were surely counted as adults. The figures include both nesting and foraging doves in each habitat. In the censuses of 1907-1909 and 1957-1958, several ground nests of the mourning dove were found in open- field habitats, but we have no way of knowing what per cent of the population found in open fields represented nesting birds. We judge that only a few habitats (shrub, orchard, urban area, and fallow field) have high nesting densities of the mourning dove, and these habitats repre- sent a small per cent of the land acreage of the state. In all but four of the summer habitats (fallow field, ungrazed grassland, red clover, and urban and rural residential areas), densities averaged higher in 1907- 1909 than in 1957-1958. There is evi- dence of a northward shift in the dove population between 1909 and 1957. In 1907-1909, population densities of the mourning dove in several habitats (pas- ture, prairie, orchard, corn, and plowed fields) tended to be highest in the south- ern zone and lowest in the northern ; in 1957-1958, dove populations in some of these habitats showed highest densities in the northern zone, lowest in the southern. For example, in pastureland in 1907- 1909 there were about 2.1 doves per 100 acres in the northern zone, 5.0 in the cen- tral, and 6.3 in the southern, but in 1957- 1958 densities were 2.^ in the northern zone, 2.'^ in the central, and 1.7 in the southern. Of all the habitats, only or- chard w'as consistent in having highest densities in the southern zone in all years. Some of the patterns of summer distri- bution seemed contradictory. Why should orchards have had highest concentrations of dove populations in the southern zone, while shrub and urban residential areas had highest concentrations in the northern zone? Some distribution patterns may have been related to habitat availability. For instance, shrub acreage was low in the northern zone, and doves may have tended to pack the available area of this excellent nesting habitat. The limited acreage of shrub areas in northern Illinois may also have accounted for the high densities of dove populations in the northern urban areas. Within a given habitat or a particular geographic area, mourning dove popula- tions may fluctuate greatly from year to year. Hanson & Kossack (1963:115-7) reported great year-to-year fluctuations in the habitats and area they studied. In the statewide and zonewide populations of the periods reported here, we found that popu- lation fluctuations in the mourning dove were remarkably small in comparison with population fluctuations in many other spe- cies. Our estimates of the statewide mourn- ing dove populations were as follows: 2,438,000 in 1909 (about 2.500,000 in 1907, as estimated from central and south- ern zone data), 2.000.000 in 1957. and 2,000,000 in 1958. Such small fluctua- tions were, perhaps, to be expected in a broadly distributed species, which may suffer losses in one zone or habitat and balance them by gains in another zone or another habitat. Because dove popula- tions varied little from one census year to the next, we believe that there was an actual decline in the state population be- tween the two census periods amounting to about 19 per cent of the 1907-1909 level. Most of the loss appears to have been in the southern zone population, which dropped from about 1,500,000 birds in 1907-1909 to about 1,100,000 in 1957- 1958. The 1957-1958 dove populations in the northern zone (about 400,000 October, 1963 Graber & Graber: Bird Populations in Illinois 471 birds) and the central zone (about 500,- 000 birds) were almost the same as the 1907-1909 populations in these zones. Winter populations of the mourning dove in the northern and central zones were sparse in all census years ; the south- ern zone had more than 90 per cent of the state population in winter. Some noteworthy changes took place between 1906-07 and 1956-57 in the winter dove population and its ecology. In 1906-07, most of the wintering doves of the state were found in one habitat, cornstalk (picked corn) fields, where pop- ulation densities were 0.7 bird per 100 acres in the northern and central zones and 35.6 per 100 acres in the southern zone. Changing agricultural methods vir- tually eliminated this preferred habitat. The agricultural replacement for cornstalk habitat was the mechanically picked corn- field, which had average densities, in 1956-57 and 1957-58, of 0.3, 0.5, and 3.7 doves per 100 acres in the northern, cen- tral, and southern zones, respectively. Population densities in other winter habi- tats in the southern zone (1956-57 and 1957-58 average) were 103.8 doves per 100 acres in shrubs, 23.1 in bean stubble, 9.0 in ungrazed grass, 8.0 in forest. 1.9 in fallow fields, 1.3 in hay, 1.0 in wheat, and 0.8 in small grain stubble. The most con- sistently used habitats were forest and cornfields in the northern and central zones and shrub-grown areas and corn- fields in the southern zone. The mourning dove apparently win- tered farther north in much higher num- bers in 1956-1958 than in 1906-07. In 1906-07, a notably mild winter, the state dove population (all habitats) numbered about 350,000 birds ; the lower popula- tion of the two later censuses (1957-58) was about 1,200,000 birds, despite the fact that weather conditions were more adverse to wintering doves in 1957-58 than in 1906-07. In both 1906-07 and 1957-58, dove populations in the northern and cen- tral zones (combined) numbered less than than 50,000 birds, a negligible part of the state total. The increase noted above was primarily in the southern zone of the state. Year-to-year variation in the winter dove population w^as high, and the dif- ference between the 1956-57 and 1957-58 populations warrants discussion. State populations in 1956-57 and 1957-58 num- bered about 2,000,000 and 1,200.000 birds, respectively. A factor that may have had some bearing on the reduced number in 1957-58 was the unusual and pro- longed cold during the fall dove migration season (1957), which may have effected a more extensive evacuation of doves from the state. In addition, our census schedule was late in 1957-58 (running into Febru- ary), and extreme cold in January and February may have pushed doves farther south. Censuses conducted in late Decem- ber, 1956, and early January, 1957, when mild winter conditions prevailed, showed a dove population for the northern and central zones of about 130,000 birds. By contrast, the populations in these zones, following prolonged cold in January and early February, 1958, were negligible. These data, coupled with the great in- crease in the population of the southern zone between the winters of 1906-07 and 1956-57, indicate that the northern edge of dependable winter range for the mourn- ing dove in Illinois is south of latitude 40 degrees. The increase that occurred in the win- ter dove population of the southern zone between 190^07 and 1956-57 is puz- zling, particularly in view of the apparent decline in the breeding population. The change follows a pattern of northward range extension which we can observe in many species of birds. Regardless of the underlying cause of the range extension, it is conceivable that the populations in- volved may tend to concentrate, that is, increase where some climatic or other bar- rier delimits the range extension. Such a mechanism may be involved in the increase in the winter dove population of Illinois. Because nesting populations of the mourning dove have low densities in open- field habitats, intensive cultivation, espe- cially when accompanied by removal of such high-density dove habitats as edge shrubs, hedgerows, and orchards, is detri- mental to the dove. Activities of the ex- panding human population in urban areas may compensate to some extent for the loss of nesting sites in rural areas, because plantings in residential urban areas have large dove populations. The mourning dove may, in fact, be adapting to this ex- panding habitat, as the early censuses 472 Ii.i.ixois Naturai- History Survey Bulletin Vol. 28, Art. 3 showed few doves in urban residential areas. Cuckoos.—In all census years com- bined, the two cuckoos were counted in a ratio of about 14 vellow-bills to 1 black- bill. The yellow-billed cuckoo occurred throuji;hout the state in summer of all cen- sus years; it was most abundant in the southern zone, least abundant in the northern. In most habitats, population densities were highest in the southern zone. In edge shrubbery in 1957-1958, there were 10.0 birds per 100 acres in the south- ern zone and 8.4 in the northern zone. Densities of yellow-billed cuckoo popu- lations in various summer habitats in the southern zone in 1957-1958 were 45.7 birds per 100 acres in hedgerows, 10.0 in edge shrubbery, 3.9 in orchards (6.6 in 1907-1909), 1.6 in shrub-grown areas (12.0 in 1907-1909), 0.8 in pastures (0.2 in 1907-1909), 0.6 in forest (3.3 in 1907- 1909). In 1907-1909 only, the yellow- billed cuckoo was found in residential habitat (6.0 birds per 100 acres), wheat fields (0.7), and mixed hay (0.5). The density data suggest that the cuckoo population declined between 1909 and 1957. Our estimates of the state pop- ulations in different vears Avere 167,000 birds in 1907, 383.000 in 1909, 92,000 in 1957, and 59,000 in 1958. The estimates indicate a notable population decrease. Habitat changes that eliminated some of the best cuckoo nesting areas in the state undoubtedly had some effect on the cuckoo population ; among these changes were the decrease in the acreage of orchards by 1958 to about one-tenth of the 1909 acre- age and the destruction of many hedge- rows and roadside shrubs along field boundaries. An increase in forest-edge habitat in southern Illinois compensated but little, for this had become a low-den- sity habitat for cuckoos. Cuckoos were found in residential areas in 1907-1909 but not in 1957-1958. The difference ma\ reflect some change in the nature of plantings near human habitations. Chimney Swift.—In all census years, the chimney swift was found in summer throughout the state. Before white settlement, chimney swifts probably placed their nests in hollow trees. They may still use such nesting sites, hut most of the population nests in man-made chimneys. This very specialized nesting habitat and the special feeding method of the chimney swift complicate discussion of populations of this species. In urban resi- dential areas in 1958, we counted 24.4 swifts per 100 acres in the southern zone, 26.8 in the central zone, but only 14.4 in the northern zone. On the other hand, population densities of the swift foraging in nonurban areas tended to be highest in the northern and central zones. The ur- ban densities were lowest where the avail- ability of nesting sites was highest. Most of the state's urban acreage is in the north- ern zone (71 per cent in northern zone, 13 per cent in central zone, and 16 per cent in southern zone). Because of its great mobility, the swift was encountered in every habitat censused. Populations were not distributed over the various habitats in proportion to the acre- age distribution of the habitats. For ex- ample, cornfields comprised the largest (in terms of acreage) single habitat in the state, and the largest habitat sampled, but only about 11 per cent of the swifts counted were over cornfields; about 35 per cent were over hayfields, which had about half the acreage of cornfields. In all census years, hayfields (various tj^pes), pasture, and fallow fields were the favored foraging habitats of the swift. Population densities of foraging swifts over hayfields of all types (an expanding habitat) were about the same (average density 3.4 birds per 100 acres) in 1957-1958 as in 1907-1909, but in pas- tureland (a diminishing habitat) swift numbers showed an increase between 1907-190^) (1.2 per 100 acres) and 1957- 1958 (4.6 per 100 acres). These obser- vations suggest that the swift has been consistent in habitat preferences through the j^ears. Populations over alfalfa were comparable to those over mixed hay. Red clover and sweet clover fields were par- ticularly favored (average density: 7.2 swifts per 100 acres) ; total clover acre- age increased between 1909 and 1957. In other habitats, densities (all census years combined) were 1.4 swifts per 100 acres in fallow fields, 1.1 in small grain, and 0.6 in corn. We do not imply by these observations that the swift consciously chooses particular foraging habitats. The October, 1963 Graber & Graber: Bird Populations in Illinois 473 distribution of foraging swifts probably reflects distribution of insect concentra- tions, which vary from habitat to habitat. It is difficult to estimate population change, if any, in the chimney swift be- tween 1909 and 1957. Population densi- ties of this species in urban areas, perhaps the best guide, were 6.0 birds per 100 acres in the southern zone in 1909 and 24.4 in the same zone in 1958. Ecological changes since 1909 appear to be highly favorable to the chimney swift. With in- creased nesting habitat arising through urbanization, and an increase in favored foraging habitats, the swift population may increase along with the human popu- lation. Yellow-Shafted Flicker. — Of the seven species of woodpeckers (yellow- shafted flicker; pileated, red-bellied, red- headed, hairy, and downy woodpeckers ; and yellow-bellied sapsucker) found with- in the census strips (all years included), the flicker was the most abundant. It was counted in all zones and years, both sum- mer and winter. The yellow-shafted flicker was found in a great variety of summer habitats, and in all of them population densities were consistently (all census years) highest in the northern zone. Densities were slightly lower in the central zone than in the northern and fell off sharply in the southern. For example, in 1909, pasture- land had 16.6 flickers per 100 acres in the northern zone, 14.9 in the central zone, but only 4.3 in the southern. Favored summer habitats of the flicker were hedgerows, savanna-type areas, edge shrubbery, residential areas, and forest. Densities of flicker populations in various summer habitats in northern Illinois in 1957-1958 were 31.4 birds per 100 acres in hedgerows, 21.6 in savanna-type areas, 8.4 in edge shrubberv, 5.6 in residential areas (27.8 in 1909),' 5.6 in forest, 3.0 in shrub-grown areas, 2.9 in pastures (16.6 in 1909), 2.2 in mixed hav (6.8 in 1909), 2.1 in fallow fields (20.6 in 1909), 1.2 in oat fields (1.2 in 1909), 1.0 in ungrazed grassland (6.8 in 1909), and 0.8 in corn- fields (2.8 in 1909). (No surveys were made in northern Illinois in 1907.) Har- vested hayfields and clover fields, which often have high bird populations, were apparently not attractive to flickers. In all habitats for which we have comparative data over the entire state, population den- sities of the flicker were much lower in 1957-1958 than in 1907-1909. As the density data imply, the state flicker population declined greatly be- tween the two studv periods, from about 2,279,000 birds in' 1909 to 300,000 in 1957 and 225,000 in 1958. Perhaps 1909 was a bumper year for flickers. The popu- lation was lower in 1907 than in 1909; yet the central and southern zones in 1907 (no census in the northern zone that year) had about 727,000 flickers, more than twice the 1957 or the 1958 population for the entire state. Causes for the decline in flicker num- bers can only be surmised. Habitat changes probably had some effect. The flicker is not strictly a forest bird. Open fields, particularly grassland, and scattered trees for nesting sites are probably the essential habitat requirements. While Illi- nois contained more forest in 1957-1958 than in 1907-1909, savanna-type situations in the state probably were greatly reduced ; tree removal from field edges and tillable land has recently been common practice in Illinois. Reduction of pasture acreage eliminated some nesting sites (scattered trees), as well as good foraging habitat. The introduction of the starling may have played a very important role in re- ducing the flicker population. Competi- tion amoni certain species for nest cavities is keen, and starlings have proved their ability to compete. Of all the Illinois picids, the flicker has been most closely as- sociated with man and is therefore proba- bly most in competition with the intro- duced bird. In the summers of 1957 and 1958, flicker populations varied from place to place in urban areas inversely with the starling populations. The change in the flicker population between 1909 and 1957 accentuated its north-south cline. The northern zone of Illinois had about 841,- 000 birds in 1909 and 186,000 in 1957; the southern zone had 445,000 in 1909 and less than 15,000 in 1957. In winter, most of the Illinois flicker population was found in the southern zone. In contrast to the summer popula- tion densities, winter densities were not consistently lower in 1956-1958 than in 1906-07. ' 474 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 In 1906-07, the picked cornHelds with stalks still standing comprised the favorite winter habitat of the flicker, as well as many other species, in southern Illinois; no other habitat boasted such a high den- sity (7.7 flickers per 100 acres in contrast to 1.7 for corn stubble only). Other fa- vored habitats were shrub areas, ungrazed grassland, forest, and pasture. Flicker population densities for these and other winter habitats in the southern zone for 1956-1958 were 6.0 flickers per 100 acres in hayfields (1.0 for 1906-07), 4.6 in shrub-grown areas, 3.8 in forest (2.5 for 1906-07), 2.2 in ungrazed grassland (6.6 for 1906-07), 2.0 in pasture (2.9 for 1906-07), and 2.0 in mechanically picked cornfields (for 1906-07, 1.7 in' stubble and 7.7 in hand-picked fields). The corn- stalk habitat, by its attractiveness and almost unlimited availability, may have been partly responsible for low densities of the flicker in other habitats in 1906-07. Winter wheat, an ample habitat in south- ern Illinois, apparently was not used by the flicker, nor were fields of small grain stubble to any considerable degree. In January, 1907, there were about 544,000 flickers wintering in the state (75 per cent in the southern zone). In Janu- ary, 1957, the state flicker population numbered about 202,000 birds (85 per cent in the southern zone). As in popu- lations of some other species, flicker popu- lations apparently shifted southward in late winter, for in February, 1958, about 394,000 birds (96 per cent of the state population) were in the southern zone and less than 20,000 in the rest of the state. Red-Bellied Woodpecker.— In 1907-1909, the breeding population of the red-bellied woodpecker in Illinois was virtually restricted to the southern zone, but, in 1956-1958, this species was found in all zones of the state. The primary habitat for the red-bellied woodpecker was forest, in which summer populations were remarkably constant at about 5 birds per 100 acres in the south- ern zone in both the early and later cen- sus years. By 1957-1958, the central zone forests also had attained densities of about 5 birds per 100 acres, but the nesting population in the northern zone was still very sparse. Because population densities of the red-belly appeared to level off at 5 birds per 100 acres in both the southern and central zones, we believe that this fig- ure represents a saturation level for the breeding population in this species. Other habitats frequented by the red- belly in summer were shrub areas and grassland, especially pasture, which were probably foraging areas (usual densities: about 2 birds per 100 acres in each of these habitats). In the winters of 1956-57 and 1957- 58, the red-bellied woodpecker populations in forest increased over the summer levels in all zones of the state. From the sum- mer density of 5 birds per 100 acres, the forest population increased by winter to 9 birds per 100 acres in the southern zone and 7 per 100 acres in the central zone. Because the red-bellied woodpecker is not a strongly migratory species, much of the winter increment probably represented local production. Both the geographical distribution (extension of the range northward) and the ecological distribution of the red-bellied woodpecker were greater in winter than in summer. Evidence of a northward extension of the population in winter was the fact that the forest popula- tion in the northern zone increased from a very sparse population in summer to about 3 birds per 100 acres in winter. Ecological extension was evident in win- ter when the red-belly was seen in shrub areas, fallow fields, pastures, and even row crops. Winter densities in nonforest habi- tats were usually 1 to 2 birds per 100 acres. The ecological extension may have represented both a wandering juvenile population and a seasonal change in for- aging habits by the total population. We estimate that the breeding popu- lation numbered about 103,000 in 1907 and 119,000 in 1909, all in the southern zone. By 1957-1958, the number of red- bellies in the state had greatly increased (to at least 198,000 in 1957 and 153,000 in 1958), with most of the population in the southern and central zones. The pop- ulation will probably continue to increase in the northern zone. Because the red- bellied woodpecker is a forest species (not associated with man), it is less in com- petition with the starling than is the flicker. Red-Headed Woodpecker.— In all census years, the red-headed woodpecker October, 1963 Graber & Graber: Bird Populations in Illinois 475 was encountered throughout the state in summer, but only in the southern and cen- tral zones in winter. In 1907-1909, sum- mer populations of the red-head were fairly uniformly distributed in the state, but, in 1957-1958, the southern zone had a negligible part of the state population. Populations of this species are notoriously variable from year to year, but, even after considering this annual variation, we believe that the red-headed woodpecker population was much higher in 1907—1909 than in the later census years. Like the flicker, the red-headed wood- pecker appeared to prefer a savanna-like situation in summer; it was found often in open fields. Favored summer habitats, in addition to savanna-type, were shrub- grown areas and forest. The red-headed woodpecker was found in virtually every habitat censused in 1907-1909, but in only a few habitats in 1957-1958. Densities of red-headed woodpecker populations in various habitats in the state in 1907-1909 were 22.1 birds per 100 acres in shrub- grown areas (1.4 in 1957-1958). 12.8 in forest (2.3 in 1957-1958), 5.8 in or- chards, 3.8 in fallow fields, 3.7 in red clover (0.7 in 1957-1958), 3.6 in pas- tures (0.2 in 1957-1958), 3.5 in ungrazed grassland (2.1 in 1957-1958), 2.7 in plowed fields, 1.8 in residential habitat (0.6 in 1957-1958), 1.5 in wheat, 1.2 in mixed hay, 1.1 in corn (0.1 in 1957- 1958), and 0.4 in oats. Savanna-like areas censused in 1957-1958 had 16.0 red- headed woodpeckers per 100 acres. The summer populations of the red- headed woodpecker in 1957-1958 were but a small fraction of those in 1907- 1909. We estimated that there were about 1,270,000 red-headed woodpeckers (breed- ing adults) in the state in Tune, 1909. but onlv 115.000 in 1957 and 134,000 in 1958. The 1907 population may have been under 1 million (no northern zone census in 1907), but it was still at least seven times as great as the 1957-1958 populations. The red-head and the flicker had a similar pattern of gross population reduction in the state, a reduction that was especially noticeable in the southern zone. These two species have certain habi- tat preferences in common ; in summer, thev, more than other species of wood- peckers, seek nonforest habitats. The in- troduction of the starling and some sub- tle, though important, habitat changes dis- cussed in the section on the flicker have probably had harmful effects. The red-headed woodpecker is migra- tory and in winter it usually vacates the northern parts of its breeding range. In winter, forest becomes the primary habitat almost to the exclusion of other habitat types. The red-headed woodpecker in Illi- nois wintered farther north in 1956- 1958 than in 1906-07. This northward extension may represent a trend, though the winter distribution of red-heads varies greatly from time to time and de- pends on availability of acorns and on other foraging conditions. In 1906-07, despite the mildness of the winter, red- heads were found in Illinois only in the southern zone, where the population num- bered only 38,000 birds, mostly in forest. By contrast with the flicker, the red-head made little use of cornstalk habitat. In 1956-1958, red-headed woodpeckers were found in forest in both the central and southern zones, and state populations num- berd 92,000 (72 per cent in the southern zone) in January, 1957, and 424,000 (98 per cent in the southern zone) in Febru- ary, 1958. The very high winter popula- tion in the southern zone in 1958 prob- ably represented a special concentration, the result of unusually good foraging con- ditions there. The central zone was vir- tually devoid of red-heads, and part of the concentration in the southern zone may have come from states adjacent to Illinois. What the future holds for this species is difficult to predict. There is some evi- dence that red-head populations reached their lowest level before 1957 (but after 1909) and that the populations have come back slightly in recent years. With com- petition for nesting cavities particularly great since the introduction of the star- ling, a notable future increase in the red- head population seems unlikely. Downy Woodpecker.—The downy woodpecker was encountered throughout the state during the surveys about four times as frequently, both in summer and winter, as its congener, the hairy wood- pecker. The downy woodpecker is primarily a forest species, and we can say little about 476 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 population cliaiip:cs, if any, between 1909 and 1957, because of the small acreage of forest sampled in summer in the earlv surveys. Our southern census samples in- dicate that the state population of the downy increased at least slightly between the two survey periods, perhaps because of the spread of forest. The geographic and ecological distribu- tion of the downy woodpecker in the re- cent surveys is of interest. In the sum- mers 1957 and 1958, downies were found in the northern and central zones only in forest, but in the southern zone in both forest and shrub areas. Population den- sities indicated that central zone forests were particularly good for downies. Forest populations were 3.4 birds per 100 acres in the northern zone, 12.2 in the central, and 2.8 in the southern. We estimated that the state breeding population of the downy was about 287,- 000 in 1957 and 219,000 in 1958. (Esti- mates of forest populations are apt to be low if based on the strip census method.) In both years, 53 per cent of the nesting population of the state was in the southern zone and about 40 per cent in the central. The downy woodpecker is supposedly not a migratory species in Illinois. In winter, the downv population, swelled bv summer production, extended into many nonforest habitats, our data showed. This ecological extension may be explained by one or more of the following: the natural overflow of a swelled population, the wandering of juveniles, or a change (from summer) in foraging habits by the total populace. Woody habitats (forest, shrubs, and orchards) had the highest population densities in winter ; such open-field habi- tats as corn stubble, fallow fields, and pasture also harbored downy populations. Winter population estimates of the downv woodpecker for the state were 322,000 birds in 1906-07, 506.000 in 1956-57, and 507,000 in 1957-58. These figures represented increases over the re- spective summer populations of about 2 to 1 ; the ratio was not the same in all zones. About 60 per cent of the state population was in the southern zone, only 10-15 per cent in the central zone, and 25-30 per cent in the northern zone. These figures mean that winter popula- tions in the northern and southern zones increased greatly over their respective summer populations, as expected, while the winter population in the central zone actually fell below the summer population there. The distribution pattern is exceed- ingly perplexing, but, because the pattern was consistent in all census years, we feel that it represents a genuine biological phe- nomenon. The data suggest that there is at least one migratory population of downies in the state ; distribution, both winter and summer, in this species needs careful and detailed study. With increased acreage of forest, and almost unlimited areas of winter forage habitats (corn, fallow fields, pasture, shrub, and forest), the future for this species looks bright. Eastern Kingbird.— Six species of summer resident flycatchers (eastern king- bird, crested flycatcher, phoebe, Acadian flycatcher. Traill's flycatcher, and wood pewee) were encountered during the sum- mer surveys. The eastern kingbird was fairly uniformly distributed in the three zones of the state in 1907-1909, but pop- ulations tended (all census years) to be most dense in the northern zone, least dense in the southern. For example, pas- tureland in 1907-1909 had 4.7 kingbirds per 100 acres in the northern zone (5.7 in 1957-1958). 3.4 in the central (1.7 in 1957-1958), and 2.5 in the southern (0.0 in 1957-1958). Populations in the south- ern zone were particularly low in the re- cent census years. In 1957-1958, shrub- grown areas had densities of 9.3 kingbirds per 100 acres in the northern zone, 8.2 in the central, and 0.8 in the southern. The eastern kingbird occurred in all census years in virtually every summer habitat censused ; particularly favored were edge shrubbery, farmyards, shrub- grown areas, savanna-type areas, and or- chards. Densities of kingbird populations in various habitats in the northern zone in 1957-1958 were 33.5 birds per 100 acres in edge shrubs, 9.3 in shrub-grown areas, 7.2 in savanna-type areas, 6.2 in fallow fields, 5.7 in pasture (4.7 in 1909). 1.8 in red clover, 1.4 in both mixed ha\ and mowed havfields (2.8 in 1909), and 0.3 in cornfields (1.7 in 1909). In 1907- 1909, farmyards of the state had 7.3 king- birds per 100 acres; orchards in the south- ern zone had 6.6 per 100 acres (3.8 in October, 1963 Graber & Graber: Bird Populations in Illinois 477 1957-1958). Frequently used (all census years) foraging habitats in the central and southern zones were plowed fields (2.5 birds per 100 acres), oat fields (1.6), and iingrazed grassland (1.4). Population densities in favorite habitats were roughly similar in 1907-1909 and 1957-1958, but densities in marginal habitats, such as cornfields, indicated that there had been a decline in the kingbird population be- tween 1909 and 1957. Our estimates of the state breeding populations of this species were 662,000 in 1909 (about 650,000 in 1907, esti- mated from central and southern popula- tions), 307,000 in 1957, and 226,000 in 1958. The decline was particularly strik- ing in the southern zone, where the king- bird population fell from about 350,000 birds in 1907-1909 to less than 100,000 in 1957-1958. Because the tyrant flycatchers are no- tably aggressive in competing with other species, competition would seem an un- likely factor in the decline of the kingbird. Habitat changes between 1909 and 1957 probably had a marked effect on the king- bird population. Areas of two important kingbird habitats, orchards and pasture- land, were reduced tremendously. An in- crease in forest areas probably eliminated some kingbird habitat, and reduction in the numbers of farmsteads and hedgerows in recent years removed some prime nest- ing habitat. It is possible that changes in the insect fauna had an effect on the king- bird population. The fact that the 1957- 1958 densities in orchards were notably below the 1907-1909 level suggests that modern methods of orchard management do not favor the kingbird. Because road- side vegetation (hedges and shrubs) pro- vides an important habitat for kingbirds, roadside spraying with herbicides and in- secticides may have played an important role in the decline. Horned Lark.—In all census years, the horned lark was recorded throughout the state, both summer and winter, in all open-field habitats. Summer population densities for the lark were notably lower (all census years) in the southern zone than in the central and northern zones. For example, cornfields in 1957-1958 had 32.9 larks per 100 acres in the northern zone and 32.2 in the central zone, but only 4.7 per 100 acres in the southern zone. In certain habitats, particularly hav types, there was marked difference be- tween northern and central zone popula- tions. In 1957-1958, population densities in alfalfa fields were 112.9 larks per 100 acres in the central zone and 11.6 in the northern ; densities in red clover fields were 96.8 in the central zone and 0.4 in the northern. Densities of horned lark populations in various summer habitats in the central zone in 1957-1958 were 149.8 birds per 100 acres in plowed fields, 112.9 in al- falfa, 96.8 in red clover, 46.6 in soybeans, 32.2 in cornfields (6.6 in 1907-1909}, 31.9 in sweet clover, 24.2 in small grain stubble, 11.4 in oat fields (5.0 in 1907- 1909), 6.0 in ungrazed grassland, 5.5 in fallow fields, 4.1 in pastures (5.4 in 1907- 1909), and 3.4 in mixed hay (0.8 in 1907-1909). In the northern zone in 1957-1958, sand prairie had 130.5 larks per 100 acres. No Illinois species increased more dra- matically between 1909 and 1957 than the horned lark. Besides the population in- crease, there was an apparent change in the habitat of the lark between the two census periods; this habitat change had great bearing on the population increase. The change was probably in progress even in 1907-1909, when the lark was much more of a grassland species than in the later census years. While the statewide population increased enormously, densities in pastureland actually decreased after 1909. From the natural grassland situa- tion, the lark has moved in increasing numbers to cultivated habitats (corn, soy- beans, and hay legumes), most of them associated with row-crop agriculture. This move was from a diminishing to an ex- panding habitat. Modern land manage- ment seems almost specifically designed to favor the lark. The row-crop acreage is excellent lark habitat in spring and early summer, but in midsummer, as the crops grow, this acreage loses its attractiveness to the lark. Harvesting of hay and small grain in midsummer opens up a vast new acreage, and the lark population shifts to the cut fields. In the northern zone in 1957-1958, mowed hayfields had 37.4 larks per 100 acres, a density about com- parable to that in row crops in early June. 478 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 The modern practice of mowinji roadsides also favors the lark. In June. 1W9, the statewide population of the horned lark was estimated to be about 842.000 birds, most of them in the northern (46 per cent) and central (38 per cent) zones. The 1907 statewide sum- mer population was hijiher, but probably numbered less than 1,500,000 larks (no census in northern zone). In June, 1957, the state population of larks numbered about 5,621,000 birds and, in June, 1958, 4,477,000. As in 1907-1909, most of the horned lark population in 1957-1958 (85-90 per cent) was in the northern and central zones, but the center of abundance had shifted southward to the central zone. The June counts did not represent strictly the breeding populace. We did not in- clude identifiable juveniles in our popula- tion calculations, but, as horned larks nest early in spring, some well-grown juveniles were probably counted as adults. Inclusion of some juveniles in the counts was prob- ably a source of some of the year-to-year variation noted above. Early spring (Feb- ruary-March) temperatures were above normal in 1957, but abnormally low in 1958. Nesting was probably delayed in 1958, and the count for that year may have included few juveniles. The entire winter and early spring of 1908-09 had abov'e-normal temperatures, and the count for June, 1909, may have had a higher proportion of juveniles than either the 1957 or the 1958 counts. Winter habitats for the lark w^ere the winter counterparts of the summer habi- tats (corn stubble or stalks, bean stubble, small grain stubble, winter wheat) and in- cluded virtually all open-field areas. In 1906-07, corn stubble, pasture, small grain stubble, and wheat, listed in order of preference, were the most favored win- ter habitats; in 1956-1958, bean stubble, alfalfa, and mechanically picked corn were the preferred habitats. Modern ag- riculture favored the lark even in winter. The cornstalk habitat (corn picked by hand and the stalks left standing), which covered much of the winter landscape in 1907-1909, was virtually unused by the lark, while the less abundant corn stub- ble was a favorite winter habitat of the species. Mechanized corn picking all but eliminated the standing cornstalk habitat, which favored many other species of birds in winter, and vastly increased a habitat that favors the lark. Winter populations of the horned lark in the state numbered about 2,416,000 birds in 1906-07, 9,175,000 in 1956-57, and 7,634,000 in 1957-58. In all census years, the ratio between winter and sum- mer populations for the state was 1.6 or 1.7 larks in January to 1.0 the following June. The constancy of this ratio is sur- prising; it may provide a clue to the re- productive increment in this species, but further study on the natural history of the horned lark is needed before we can un- derstand the significance of the ratio. Al- though this ratio was constant from year to year, it was not constant from zone to zone. The winter-summer ratios for the different zones imply that horned lark populations in the northern part of the state shifted southward in winter. In 1956-57, for example, the northern zone had only 0.6 lark in January to 1.0 in June and the central zone had 1.3 larks in win- ter to 1.0 in summer; the southern zone had 6.5 larks in winter to 1.0 in summer. At the time of the recent survey, the fu- ture outlook for the horned lark in Illinois appeared to be entirely favorable. Barn Swallow.—Of the six species of swallows (tree, bank, rough-winged, barn, and cliff, and the purple martin) encoun- tered in the summer surveys, the barn swallow was undoubtedly the commonest member of its family. At the time of the early series of censuses, this bird was most abundant in the northern zone and least abundant in the southern. In the 50 years that followed, this species increased in numbers, particularly in the southern zone. In 1957-1958, the barn swallow was most abundant in the southern zone, least abundant in the northern. Population densities of the barn swallow over alfalfa fields in 1957-1958 were 4.4 birds per 100 acres in the northern zone, 24.0 in the central zone, and 38.8 in the southern zone. The barn swallow was seen foraging in summer in a great variety of open-field habitats; it favored edge shrubs, alfalfa, sweet clover, pastures, and ungrazed grass- lands. Population densities for various foraging habitats of the state in 1957- October, 1963 Graber tSc Graber: Bird Populations in Illinois 479 1958 were 26.3 swallows per 100 acres over edge shrubs, 13.1 in alfalfa, 11.8 in sweet clover, 9.6 in pastures (1.7 in 1907- 1909), 7.5 in ungrazed grasslands (27.0 in 1907-1909), 4.2 in red clover (5.2 in 1907-1909), 4.2 in mixed hav (3.3 in 1907-1909), 3.5 in oats and wheat (0.5 in 1907-1909), 3.4 in fallow fields (6.2 in 1907-1909), and 1.7 in corn and soy- beans (0.2 in 1907-1909). Ungrazed grassland, fallow fields, and red clover, the favored habitats in 1907-1909, ap- parently lost some birds to alfalfa, a crop that increased greatly after 1909. Edge habitats, such as roadsides and drainage ditches, appeared to have high numbers of foraging barn swallows. Cutting enhanced fields of wheat and hay as foraging areas for swallows. State population estimates for this spe- cies were 300,000 birds in June, 1909, and 910,000 in June, 1957. The 1907 popula- tion was probably even lower than 300,- 000 (no northern zone census in 1907), and the 1958 population was probably over 1,000,000. The barn swallow is an- other of the species that increased greatly between the early and later surveys. Not only did population densities of the barn swallow in some favored foraging habitats (notably pastureland) increase between the two census periods ; certain habitat changes favored the barn swallow. Alfalfa, one of the best habitats, became a dominant hay crop in Illinois, and other hay crops proved to be good foraging habi- tats for the barn swallow. Barns, important nesting sites for the barn swallow, were probably less plentiful in 1957-1958 than in 1907-1909, but ce- ment culverts and bridges were more nu- merous. The barn swallow may recently have made increased use of culverts and bridges for nesting sites. The increasing use of potent insecticides may ultimately create problems in food acquisition for the barn swallow and other insectivorous birds, but land management practices in Illinois in 1958 appeared to favor the barn swallow and some other species of swallows. Blue Jay.—The blue jay was recorded throughout the state, both summer and winter, in all census years. In summer, the jay occurred in a va- riety of woody and open-field habitats and showed some interesting regional varia- tions in habitat preference. For example, in cornfields, a marginal foraging habitat, the jay was notably more numerous in all census years in northern Illinois than in the central or southern zones. In forests, population densities of the jay were high- est in the central zone, lowest in the southern; in urban residential areas, jay populations were most dense in the south- ern zone. In some other habitats, pasture- land, for example, there was little varia- tion in the jay population from one zone to another. In most summer habitats for which comparative figures are available, blue jay population densities were higher in 1907- 1909 than in 1957-1958. In 1907-1909, the most favored blue jay habitats were forests, orchards, and residential areas. In 1957—1958, the species was numerous in residential areas and in hedgerows and edge-shrub habitat (neither of the last two habitats was censused in 1907-1909). Summer population levels of the blue jay in various habitats of the state in 1957- 1958 were 67.6 birds per 100 acres in hedgerows, 30.0 in edge shrubs, 17.7 in residential areas (11.9 in 1907-1909), 8.0 in savanna-tvpe areas, 6.6 in forest (33.3 in 1907-1909), 4.1 in orchards (20.7 in 1907-1909), 3.2 in shrub areas (16.1 in 1907-1909), 1.4 in pastureland (2.5 in 1907-1909), 0.4 in fallow fields (2.5 in 1907-1909), and 0.3 in cornfields (1.1 in 1907-1909). The state blue jay population declined greatly between 1909 and 1957. Our esti- mates of the state population were 1,300,- 000 in 1907 (estimate based on central and southern zone populations), 1,557,- 000 in 1909, 460,000 in 1957, and 470,- 000 in 1958. The loss was apparent in all zones, but it was particularly great in the southern zone (81 per cent decline in southern zone, 47 per cent decline in northern and central zones). The population decline in this species is surprising. The blue jay is a versatile species, nesting as it does in a variety of woody habitats. Forest, a favored habitat in 1907-1909, increased in acreage, but jav populations in forest had become rela- tively sparse by 1957. In orchards, a diminished habitat, recent jay populations were thinner than those of 1907-1909. 480 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 The ecology of the blue jay appears to be chanjiino;. Of all its summer habitats, only residential areas appeared to have higher populations in the recent census years than in 1907-1909. In northern Illi- nois in 1907-1909, the bulk of the jay population was in forest, but, in 1957- 1958. most of the population was in resi- dential areas. The causes for this change are not apparent. Gross habitat changes since 1909 appear to have been beneficial, not harmful. The fact that the jay pop- ulation thinned in favorite habitats sug- gests such possible causative factors as competition, reduced availability of food, or disease (in essence, reduced productivity or increased mortality). We can only sug- gest that further study of this species is needed. Some blue jay populations are migraton^ The jays that winter in Illinois could rep- resent breeding populations from states to the north, resident Illinois populations, or a combination of the two population groups. In 1906-07, the winter population of jays was estimated to number 833,000 birds (compared to 1,300,000 the follow- ing June) ; about 81 per cent of the state winter population was in the southern zone. In 1956-57 and 1957-58, the state winter populations (461,000 in 1956-57, 570,000 in 1957-58) were slightly higher than breeding populations in the follow- ing summers, but. like the summer popu- lations, still far below the levels of the early census years. To determine pre- cisely what happens in these population shifts and changes, there is need for an intensive blue jay banding program. The principal winter habitats of the blue jay in all census years were shrub, forest, and orchard. Jays made relatively little use of open-field winter habitats in the recent census years, although in 1906- 07 they had frequented (in sparse num- bers) cornstalk habitat and pastureland. Gross changes in winter habitats do not appear to have been responsible for reduc- ing the jay population. Common Crow. — In summer and winter (all census years), the common crow was counted within the census strips in all zones of the state and in virtually every habitat. Crow distribution in the three zones was quite uniform, reflecting total acreage distribution ; largest numbers of crows were in the southern zone, small- est in the northern, both summer and winter. Hedgerows, orchards, and forests were the habitats with the highest population densities of crows. Populations in most habitats were higher in 1907-1909 than in 1957-1958. Densities of crow popula- tions in various summer habitats of the state in 1957-1958 were 15.0 birds per 100 acres in hedgerows, 5.4 in forest (6.4 in 1907-1909), 3.6 in sweet clover, 2.7 in ^ plowed fields, 2.1 in ungrazed grassland and marshland, 2.0 in edge shrubs, 1.9 in shrub-grown areas (4.7 in 1907-1909), 0.5 in pastures (2.2 in 1907-1909), and 0.5 in cornfields (1.7 in 1907-1909). In addition, in 1907-1909, crows were found in orchards (13.5 per 100 acres), cut and shocked wheat fields (8.9 per 100 acres, in contrast to 0.2 in standing wheat), red clover (2.5). fallow fields (1.8), oat fields (1.7), and mixed hay (1-2). Like the blue jay, the crow should pre- sumably have benefited from gross habitat changes in the half century between census periods but, like the jay, the crow ap- parently declined in numbers. In June, 1909, the state crow population, accord- ing to our estimate, numbered about 1,- 227,000 birds. In June of 1957 and 1958, state crow populations were, respectively, 342,000 and 290,000 birds. There was no northern zone census in 1907, but crow populations in both 1907 and 1909 were well above the 1957-1958 levels. Gross habitat changes, except possibly those that reduced food resources, prob- ably were not the primary causes of the decline. In terms of percentage, the de- cline was about the same in the two cor- vids, the blue jay and the crow. Both species showed declines in population den- sity in favorite habitats. In winter, crows were distributed throughout the state in all census years, but the central zone had by far the larg- est part of the state population. In all census years, also, the state crow popula- tion in winter was at least two to four times as large as that in the following summer. Estimates of the state January populations were 4,805,000 in 1907 and 1,387,000 in 1957. In February, 1958, the crow population numbered about 443,000, a figure implying that dispersal of the October, 1963 Graber & Graber: Bird Populations in Illinois 481 winter population was well along at that time of year. Much of the difference between the winter populations and the summer popu- lations must represent immigration of crows from breeding grounds north of Illinois. Cornstalks, corn stubble, small grain stubble, pasture, and forest were found to be important winter habitats for the crow. Like the summer data, the winter popu- lation figures show that crow numbers decreased between the two census periods. Furthermore, in terms of percentage change, the winter population decline matched the summer population decline almost exactly: summer, 72 per cent de- cline; winter, 71 per cent. Because some of the winter crow population in Illinois comes from other breeding grounds, these data imply that the decline in crow num- bers occurred over a broad geographic area. Gross changes in winter habitats be- tween 1909 and 1956, which should have favored the crow, offer no explanation for this decline. There was more woodv cover in 1956-1958 than in 1906-1909. and food was probably more abundant in re- cent years as use of mechanical harvesting techniques increased. The causes of the decline, whatever they were, may have been the same as those that caused a de- cline in the blue jay. Chickadees.—Both species of chicka- dee, the black-capped and the Carolina, were recorded in summer and winter within the census strips, but nonsinging chickadees are so difficult to identify to species that we have had to combine data for the two species. Chickadees in the northern zone were undoubtedly black- caps. The Carolina was probably the com- mon breeding species in the southern zone. Both species occurred in the central zone, and, in winter, both may have occurred in the southern zone. In summer, chickadees were virtually restricted to habitats with some woody cover (forest, orchard, shrubs, and, to a much lesser extent, pasture). Because forest census samples were small in 1907- 1909 (though probably adequate in the southern zone), we shall place emphasis on the recent population data. Population densities, especially those for the black-cap in the northern zone, were remarkably similar in 1957 and 1958. In forest, the principal habitat, chickadee summer popu- lations in 1957-1958 were 15.8 birds per 100 acres in the northern zone (black- cap), 10.3 in the central zone (both species), and 11.3 in the southern zone (Carolina). In shrub areas, summer den- sities were 6.2 chickadees per 100 acres in the northern zone, 8.2 in the central, and 8.7 in the southern. In edge shrub, sum- mer densities were 16.7 per 100 acres in the northern zone and 30.0 in the south- ern. The data suggest that the Carolina chickadee may make greater use of shrub habitats than does the black-cap. Neither species of chickadee was reported in resi- dential areas to a significant extent in either census period. The available data suggest that the Carolina chickadee was more numerous in 1957-1958 than in 1907-1909. In the southern zone, the summer population of the Carolina chickadee did not number more than about 78,000 birds in 1907- 1909, according to our estimate ; chickadee populations of the southern zone num- bered about 400,000 birds in 1957 and 300,000 in 1958. Even if the forest seg- ment of the chickadee population for 1957-1958 were disregarded, the recent populations would exceed those of the early census years. Because the forest cen- sus sample for northern and central Illi- nois was small in 1907-1909, and because the black-cap is definitely a forest species, we cannot speculate on population trends in this species. It is worthwhile to consider the 1957- 1958 data on chickadee populations in more detail. Chickadee distribution tended to follow the distribution of woody habi- tats (greatest number of chickadees in the southern zone, smallest number in the northern). Far more summer habitat was available to the Carolina (in the southern zone) than to the black-cap (in the northern). The "unbalanced" habitat dis- tribution may in part account for the higher black-cap population densities in the northern zone. We estimated that in summer the state population of chickadees (both species) numbered about 600,000 in 1957 and 460,000 in 1958. The north- ern zone had only about 82,000 chickadees (black-cap) in each year, while the south- 482 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 ern zone had about 400,000 (Carolina) in 1957 and 300.000 in 1958. The central zone had about 120,000 birds (both spe- cies) in 1957 and 80,000 in 1958. In winter (all census years) chickadees invaded a large number of habitats, in- cluding fallow fields, corn stubble, hav- fields, and even bean stubble and plowed fields, but, as in summer, woody types comprised the principal habitats. Chickadees (at least the black-cap) ap- peared to be somewhat migratory. From the summer population levels in 1957, the 1957-58 winter chickadee populations de- clined in the northern zone, remained about the same in the central zone, and doubled in the southern. Migration is im- plied in these data ; in a nonmigratory spe- cies, we should expect that in each zone the winter population would be greater than the previous summer population. The census data indicate that there was some change in numbers of the black- cap, or in distribution of the black-cap, between 1907 and 1956. In both 1906-07 and 1956-57, the state winter population of the chickadees (both species) num- bered about 1,000,000 birds, but chickadee distribution was very different in the two years. January populations for the north- ern zone were 230,000 in 1906-07 and 63,000 in 1956-57; for the central zone, 226,000 in 1906-07 and 105,000 in 1956- 57 : and. for the southern zone, 660,000 in 1906-07 and 830,000 in 1956-57. In January, most of the chickadees in the northern and central zones must have been black-caps, and their numbers were about three times as great in 1906-07 as in the recent census winters. Without bet- ter summer data, we cannot sa\ that this apparent decline represents a real change in total numbers of the black-cap; the difference between the 1906-07 and 1956- 57 populations may represent a change in winter distribution of the black-cap, or merely "natural" annual variation. Addi- tional information is needed on the distri- bution of both species of chickadees, par- ticularh' on their migrations. Tufted Titmouse. — The tufted tit- mouse, like the chickadees, is primarily a forest species. It is virtually restricted to habitats with some woody cover. We have meager summer data on this species for 1907-1909, except for the population of the southern zone. In recent censuses, the tufted titmouse was found in all three zones of the state, but populations were very low in the northern zone. For example, summer population densities (1957-1958) in forests were about 20 titmice per 100 acres in the southern and central zones and only 0.6 per 100 acres in the northern zone. Southern zone popu- lations of the titmouse in various summer habitats in 1957-1958 were 19.3 birds per 100 acres in forest (14.2 in 1907-1909), 9.4 in shrub-grown areas (5.3 in 1907- 1909), 5.1 in edge shrub and residential areas, and 1.3 in orchards (13.3 in 1907- 1909). A density of about 20 titmice per 100 acres may represent a kind of satura- tion level for central and southern Illi- nois forests. The recent thinning of popu- lations in orchards (despite increases in other habitats) is a pattern observable in other species, as well as the titmouse. The tufted titmouse increased in num- bers between 1909 and 1957, at least in the southern zone, where the June popu- lation was about 324,000 birds in 1907- 1909 and 550,000 in 1957-1958. There is no reason to doubt that the population increased northward, also. In 1957-1958, there were about 200,000 titmice in the central zone and about 20,000 in the northern. Our estimates for the entire state were 752,000 titmice in 1957 and 756,000 in 1958. If these figures are rep- resentative, they indicate that the titmouse population is one of the least variable for which we have data. The increase in forest acreage has surely been beneficial to the titmouse, but the fact that forest populations of this species increased in density shows that other factors than habitat change entered into the population increase. Both the tit- mouse and the Carolina chickadee are cavity nesters. Because of their small size, they probably have little competition from the larger forest species, but they may compete with one another. The northward advance of the titmouse may have had some effect on the black-capped chickadee. The occurrence of the titmouse (but not the chickadees) in the urban residential areas censused is of ecological interest ; at present this habitat accounts for only a very small fraction of the titmouse popu- lation of the state. October, 1963 Graber i: Graber: Bird Populations in Illinois 483 Winter distribution of the tufted tit- mouse through the state, the survej's showed, was similar to the summer dis- tribution. In winter, the titmouse held to the woody habitats more than did the chickadees. The tufted titmouse is not known to be migratory; yet, in both of the recent census years, the state winter population was below the following sum- mer population. We estimated that the state population of the titmouse numbered about 670,000 birds in January, 1957 (750,000 the following Tune), and 470,- 000 in February, 1958 (760,000 the fol- lowing June). Such a pattern of seasonal fluctuation suggests the possibility of mi- gration. There are few other data to cor- roborate such a view, and we should con- sider other possibilities. The titmouse probably begins nesting in April, and the February census figure may represent the adult breeding population better than the June figure. By June, many juveniles may be flying; the juvenile plumage in this spe- cies is similar to the adult plumage, and the June count may include many im- matures. Mockingbird.—In summer of all cen- sus years, the mockingbird was encoun- tered in central and southern Illinois, but, in winter, this species was seen within the census strips only in the southern zone. The central Illinois population was al- most negligible in the early census years; in 1957-1958, population densities of the mocker in central Illinois were only about one-third of the southern Illinois densities. Principal summer habitats for the mockingbird were residential areas and or- chards in 1907-1909 and edge shrubs (not censused in 1907-1909) in 1957-1958. Densities of mockingbird populations in various habitats of southern Illinois in 1957-1958 were 40.5 birds per 100 acres in edge shrubs, 2.6 in orchards (17.7 in 1907-1909), 1.0 in residential habitat (24.2 in 1907-1909), 0.8 in pastures (2.7 in 1907-1909), 0.8 in shrub-grown areas (2.7 in 1907-1909), and 0.4 in cornfields (2.5 in 1907-1909). In addition, in 1907- 1909. fallow fields had 4.1 mockers per 100 acres, and plowed fields had 2.2 per 100 acres. The density data indicate a decline in the state mockingbird populations between 1909 and 1957. Our estimates of summer populations in the southern zone were 184,000 in 1907, 386,000 in 1909, 89,000 in 1957, and 54,000 in 1958 (the 1907- 1909 figures do not include edge shrub, but the J 957-1 958 figures do). While mockingbird numbers for the state and for the southern zone diminished between 1909 and 1957, the numbers for the cen- tral zone increased notably. In the sum- mers of 1907-1909, there' were probably fewer than 5,000 mockers in the central zone, but northward extension brought the number in this zone to about 31,000 birds in 1957. The number was down in 1958 (perhaps as low as 15.000), but it still far exceeded the 1907-1909 level. Even with the geographically extended population, the total number of mocking- birds in the state in 1957 (120,000) was below the 1907 figure (more than 184.- 000). The combination of geographic ex- tension and thinning population can be observed in a few other species, for ex- ample the turkey vulture. Why the mock- ingbird population thinned in the south- ern zone we cannot say. Except for or- chards and pastureland, mockingbird habi- tats should have been nearly as extensive in 1957-1958 as in 1907-1909. The spe- cies now seems overly dependent on one type of habitat, edge shrubs, a habitat that is being eliminated by modern farming practices. A hopeful development is the increase in recent years of multiflora rose hedges, which are much favored by the mockingbird. By winter each year, the mockingbird population has shifted southward in Illi- nois, and, though a few birds may winter in the central zone of the state, the spe- cies was recorded within winter census strips in 1906-07, 1956-57, and 1Q57- 58 only in the southern zone, in habitats that were the winter counterparts of the summer habitats. The mockingbird popu- lations in Illinois numbered about 63,000 birds in January, 1907, and 39,000 in January, 1957. The population level in February, 1958, was much higher (187,- 000), probably because spring migration was under way and migrants were concen- trated in the latitudes of southern Illinois. Catbird.—In all census years, the cat- bird was found throughout the state in summer. It occurred in a variety of habi- tats (urban areas, forest, orchards, shrubs. 484 Illinois Natural History Survey Bulletix Vol. 28. Art. 3 pastures, oats, wheat, corn, hayfields, and marsh), but in greatest densities in woody types. Population densities varied greatly from zone to zone and in no consistent pattern. In the summers of 1957-1958, densities in forest were 2.2 catbirds per 100 acres in the northern. 7.5 in the central, and 0.3 in the southern zone; densities in resi- dential areas were 0.6 in the northern, 4.0 in the central, and 22.4 in the southern zone. Catbird populations in various woody habitats in southern Illinois (the zone for which we have the best data for both census periods) were, for 1957-1958, 22.4 birds per 100 acres in residential areas (12.1 for 1907-1909), 5.1 in edge shrubs (14.3 for 1907-1909), 2.6 in or- chards (26.5 for 1907-1909), and 0.8 in shrub-grown areas (2.0 for 1907-1909). In northern and central Illinois, the cat- bird (like the brown thrasher, but unlike the mockingbird) greatly favored hedge- rows (1957-1958 population density: 152.7 catbirds per 100 acres). In northern Illinois, wheat fields were a favorite for- aging habitat. We estimated that the statewide sum- mer population of catbirds numbered about 196,000 in 1957 and 220.000 in 1958. We lack data on the prime woody habitats in northern and central Illinois for 1907- 1909, but, even without the catbirds in these habitats, the state population in 1909 numbered at least 278,000 catbirds. The 1907 population was lower (no northern zone census in 1907), but probably it was close to 200,000. If we make allowance for the uncensused woody habitats, we conclude that the catbird population in the state declined considerablv between 1909 and 1957. Brown Thrasher. — Of the three mimids (mockingbird, catbird, brown thrasher) in Illinois, the brown thrasher was by far the most abundant in all cen- sus years. The thrasher occurred in sum- mer in all zones of the state, but, in 1907- 1909, most of the state population was in the southern (especially) and central zones. The brown thrasher was counted in all summer habitats except soybean fields, but this species particularly favored hedge- rows and edge shrubs. Population densi- ties varied from zone to zone and in fa- vorite habitats tended to be highest (all census years) in the central and southern zones. In 1957-1958, thrasher populations in hedgerows were 62.9 birds per 100 acres in the northern, 188.7 in the central, and 137.0 in the southern zone; in edge shrubs, 60.9 in the northern, 68,5 in the central, and 75.9 in the southern zone; in shrub areas, 27.8 in the northern, 12.2 in the central, and 2.4 in the southern zone. In other habitats, densities tended to be more nearly uniform from one zone to another. Densities of brown thrasher populations in various summer habitats of the state for 1957-1958 were 11.6 birds per 100 acres in orchards (23.2 for 1907-1909). 3.6 in sweet clover. 3.5 in residential areas (23.8 for 1907-1909), 2.1 in forests (15.4 for 1907-1909), l.b in fallow fields (2.7 for 1907-1909), 1.0 in pastures (4,9 for 1907-1909), 0.4 in alfalfa, 0.3 in corn (1.6 for 1907-1909), 0.0 in red clover (8.0 for 1907-1909). 0.0 in mixed hav (2.9 for 1907-1909). Ecologically, the thrasher was the most broadly distributed of the mimids. As the density data imply, the brown thrasher population declined greatly be- tween 1909 and 1957; the decline in this species was more marked than in either of the other mimids. State summer popula- tions, according to our estimates, were about 1,558,000 thrashers in 1909 (1,- 172,000 in 1907 in the central and south- ern zones), 431,000 in 1957, and 402,000 in 1958. The 1907-1909 estimates do not include birds in the' high-density edge- shrub and hedge habitats; so the differ- ence between populations in the two pe- riods was even more marked than our figures show. Habitat changes, such as the reduction in orchard acreage and the elimination of many hedges, undoubtedly affected brown thrasher numbers, but such changes could account for only a small part of the total population loss. As in the other Mimidae and some of the other species studied, the thrasher's population decline, though gen- eral, was particularly marked in the south- ern zone of the state. To explain these changes, we need to know more about the basic biology of each species. Perhaps we are seeing the mimid population and the population of some other species in a pe- October, 1963 Graber & Graber: Bird Populations in Illinois 485 riodic low; in the future, the numbers may increase or they may continue to de- cline. Whatever the trend, the need for future measurements of the populations is certainly indicated. Robin.—Of the three thrushes (wood thrush, robin, and bluebird) recorded as nesting in Illinois in all years of the sur- veys, the robin was by far the most abundant. In summer, the robin was found throughout the state in most of the habi- tats censused. Residential areas were clear- ly the favorite robin habitat in summer, at least in recent years. Orchards, edge shrubs, and hedgerows also were high density habitats. Robin populations varied from zone to zone. In 1907-1909, popu- lation densities tended to be highest in the southern zone of the state, lowest in the northern zone. In 1957-1958, densities tended to increase with north latitude. Residential areas in 1907-1909 had 27.8 robins per 100 acres in the northern, 33.5 in the central, and 36.3 in the southern zone, while, in 1957-1958, these areas had 132.2 in the northern, 108.6 in the central, and 101.9 in the southern zone. In forest, the 1907-1909 summer den- sities were 6.4 robins per 100 acres in the central and 15.0 in the southern zone; the 1957-1958 summer densities were 6.1 in the central and 0.3 in the southern zone. Robin numbers apparently increased greatly in residential areas between 1909 and 1957, but, in many other habitats, the numbers were greater in the early than in the later census years. Summer den- sities in various habitats of the state for 1957-1958 were 60.0 robins per 100 acres in hedgerows, 24.6 in edge shrubs, 6.6 in orchards (34.9 for 1907-1909), 5.1 in ungrazed grassland in the northern and central zones (6.8 for 1907-1909), 1.9 in pastureland (7.3 for 1907-1909), 1.9 in shrub-grown areas (3.1 for 1907- 1909), 1.8 in mixed hav (1.8 for 1907- 1909), 1.4 in red clover (4.3 for 1907- 1909), 0.9 in corn (1.6 for 1907-1909), and 0.7 in oats (0.5 for 1907-1909). Population densities of the robin in most summer habitats decreased between 1909 and 1957. We estimated that the state population in June numbered about 1,900,000 robins in 1909 (in 1907 prob- ably about 1,400,000), 1,500,000 in 1957, and 1,360,000 in 1958. The geographic and ecological distribution of the robin seems to have changed. In the summers of 1907 and 1909, the robin population was fairly uniformly distributed through- out the state. Forest and pastureland ac- counted for the bulk of the 1907-1909 summer population, but the robin was well represented in a variety of other habitats. It was an ecologically broad spe- cies. In 1957-1958, most (65 per cent) of the Illinois robins were in the northern zone. The robin was primarily (75 per cent of the state population) an inhabitant of man's communities (urban residential areas and farmyards). Reduction of pas- tureland probably hurt the robin, but residential areas provided the essential requirements (tree nesting sites and clipped grass foraging areas) of the pasture habi- tat and perhaps improved on this habitat. One possible disadvantage of this speciali- zation in habitat is that the use of chem- icals (insecticides and herbicides) toxic to robins is especially prevalent in urban areas. Except for the possible danger from these chemicals, the future for the robin seems bright. In the coming decades, ur- ban areas are sure to increase. In winter, a few robins may be found even in the northern zone of the state, but, within the census transects, this spe- cies was found in only the southern zone in the winter of 1906-07 and in only the southern and central zones in the winters of 1956-1958. The primary winter habi- tats of the robin were picked (cornstalk) cornfields, forest, and orchards in 1906- 07 and shrub areas, forest, and pastures in 1956-1958. The robin may have wintered farther north in greater numbers in recent years than at the time of the early survey. In 1906-07, a notably mild winter, the Illi- nois robin population in January (none recorded in any zone but the southern) was probably less than 100,000 birds. The number of robins in the state in January, 1957, was estimated to be 1,366,000 (all but 15,000 in the southern zone). This population was about the same as the June, 1958, population for the state. In February, 1958, the number of robins was down to 664,000 (none recorded in the central or northern zones). Because the February population showed no north- 486 Illinois Natural History Survey Bulletix Vol. 28, Art. 3 ward shift, we presume that many winter- in{i robins drifted southward in late win- ter before the onset of sprinjj; mijjration. This pattern of movement was similar to that in a number of other species. Eastern Bluebird.— In both survey periods, the eastern bluebird was found throuj2;hout the state in summer and win- ter; population densities in summer tended to be hijihest in the southern zone and lowest in the central. In most years the southern zone had the bulk of the state population, but in 1958 the bluebird sud- denly all but disappeared from southern Illinois. Favorite summer habitats of the blue- bird were edge shrubs, forest, pastures, and fallow fields, but the bluebird was found also in cornfields, plowed fields, oats, mixed hay, red clover, and marsh. Densities of bluebird populations in var- ious habitats in the southern zone for 1957 were 8.3 birds per 100 acres in pas- tures (2.8 for 1907-1909), 2.6 in fallow fields (3.7 for 1907-1909), 1.7 in forest (6.7 for 1907-1909), 1.5 in shrub-grown areas (1.8 for 1907-1909). and 0.0 in corn (1.7 for 1907-1909). Roadside habi- tats are well-known favorites of the blue- bird, and in 1957. along roads in south- ern Illinois, shrub areas had 33.6 blue- birds per 100 acres and ungrazed grass areas had 10.3 per 100 acres. Most density figures were higher in the early than in the recent surveys. A notable exception to the trend was the recent high-density fig- ure for pastureland. The great loss in pastureland acreage between 1909 and 1957 could have had some concentrating effect on the bluebird population. In June, 1909, the number of bluebirds in Illinois was estimated to be 460,000 (70 per cent in the southern zone) ; the population was higher in 1907 (no north- ern zone census), possibly as high as 600,- 000. In Tune. 1957. the state had about 220,000 'bluebirds (80 per cent in the southern zone) ; by the following summer the population had fallen to an almost unbelievable low of about 50,000 birds. Strangely, the northern zone population was still intact, but the central zone popu- lation was badly decimated and the south- ern zone population was virtually gone. We would have been inclined to doubt our census data, except that at about the same time sharp declines were noted widelv bv field observers in the eastern United States (James 1962:308). As of October. 1962. the Illinois bluebird popu- lation had shown only slight recovery. In winter (all census years), the south- ern zone had virtually all of the blue- birds in Illinois. The birds were en- countered usually in small flocks and in a variety of winter habitats. In all census years, they frequented forests, shrub areas, ungrazed grasslands, and pasture; in re- cent census years, alfalfa fields. The win- ter populations of the bluebird in Illinois were remarkably similar in the census vears, numbering about 680,000 in Jan- uary, 1907 and 1957. and about 720.000 in February, 1958. The number of blue- birds w^intering in the northern and cen- tral zones (combined) did not exceed 25.- 000 birds in any census year; in February, 1958, we found no bluebirds outside the southern zone. In comparison with popu- lations of other years, the winter popula- tion of 1957-58 in the southern zone appeared to be about normal as late as mid-February; yet the breeding popula- tions of the southern zone and most of the central zone never appeared. What happened to these populations remains a mystery. Diminished food resources in some areas, coupled with the enduring severe cold of January - March, 1958, would certainly have taken a toll; a num- ber of authors have discussed weather that was harmful to the bluebird (Mus- selman 1941 :409-10 ; Hancock 1888:433; and others). James (1962:310), in dis- cussing the decline of the bluebird popu- lation in relation to weather, suggested that something other than severe weather alone was responsible for the decline. There is evidence other than the Illi- nois census data that the decline in blue- bird numbers has been in progress for a long time. Writing about 50 years ago, Barnes (1912:328) felt that the bluebird as a nesting bird was not one-tenth as common as 20 years before and, a few years later, Ridgway (1915:196) noted that the bluebird had been "mainly dis- placed" by another cavity nester, the house sparrow. Starling.—Shortly after being intro- duced successfully into the United States (New York) in 1890, the starling began October, 1963 Graber & Graber: Bird Populations in Illinois 487 to extend its range westward. The species had not reached Illinois at the time ot the first survey (1906-1909); it was evi- dently rare in this state in 1926 (Eifrig 1927:432). Today, it is one of the most abundant species in Illinois. Both in sum- mer and winter of 1956-1958, starlings were seen throughout the state in virtu- ally every habitat. In summer, we found, no other Illinois habitat was as important to the starling as urban areas, and, to a large extent, the distribution of this habitat influenced the distribution of the breeding populations of the starling in the state. Our data on population densities of the starling in dif- ferent habitats suggest that there was some notable regional variation in the ecology of this bird. In the southern zone, for in- stance, the starling was even more decid- edly an urban resident than in the north- ern and central zones. Urban area densi- ties were about 120 starlings per 100 acres in the northern and central zones and 180 per 100 acres in the southern. In rural habitats, starlings in the southern zone had notable populations in orchards (30.9 per 100 acres, in contrast to 13.6 in the central zone), edge shrubs (high popula- tions in all zones), and corn (8.5 per 100 acres, in contrast to 0.2 in the central zone). For central zone starlings, hay- fields were consistently the favored rural habitats. Starling densities in various types of hay were as follows for the cen- tral zone: 117.1 birds per 100 acres in mowed hay (44.0 for the northern, 0.0 for the southern), 97.9 in red clover (10.9 for the northern, 0.0 for the southern). 48.0 in alfalfa (4.4 for the northern, 0.0 for the southern), and 3.6 in mixed hav (0.7 for the northern, 1.7 for the south- ern). For starlings in the northern zone, the principal rural habitat was pasture- land; densities were 17.5 starlings per 100 acres in the northern zone, 2.9 in the cen- tral, and 3.3 in the southern. Regional variations in starling ecology may be based on the timing of the breeding season (at dififerent stages in the breeding cvcle. star- lings may forage in different areas). The subject deserves detailed study. Starling populations, even in summer, were extremely variable from place to place and from year to year. This varia- bility reflected the extreme gregariousness (especially great in winter) of the species. Our population estimates for the starling are therefore particularly rough. In Illi- nois, starlings begin nesting in March and April, and by June they have some young on the wing. As the juvenile plumage is distinctive and fairly long-retained, we could segregate juveniles from adults. Our estimate of the state breeding popu- lation, 3,100,000 birds, did not include farmyard habitat, a habitat that may total nearly 200,000 acres and probably harbors a large number of starlings. In winter, the starling was found throughout the state, but, like many other species, it was most abundant in the south- ern zone. In all zones, the most consist- ently favored winter habitat of those cen- sused was small grain stubble. Fallow fields and shrubbery (all types) were also high density habitats in winter. We esti- mated that the state population of star- lings in January, 1957, may have exceeded 1 1,000,000 birds, over 90 per cent of them in the southern zone. We have inadequate winter data on urban areas, and, consid- ering the extreme gregariousness of the starling in winter, we believe this esti- mate may be very unreliable; however, there can be no doubt that the starling is near the top of the state list of birds in terms of abundance. Yellowthroat.—Of the 22 species of warblers encountered in the course of the surveys (all years), the yellowthroat was the most widespread, ecologically as well as geographically. The yellowthroat was found throughout Illinois in summer, but most of the state population was in the southern zone ; densities tended to thin northward. Many of the warblers are primarily forest species, but the yellow- throat frequents a variety of open-field habitats. Edge shrubs, probably the most consist- ently favored yellowthroat habitat, had summer population densities of 24.7 birds per 100 acres in the northern, 106.6 in the central, and 120.0 in the southern zone in 1957-1958. Southern zone population densities of the vellowthroat in various other habitats in "1957-1958 were 139.0 birds per 100 acres along drainage ditches, 91.3 in hedgerows, 84.9 in marshes (9.3 in 1907-1909), 10.9 in shrub-grown areas (26.4 in 1907-1909), 5.9 in red clover, 488 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 ^.9 in orchards (6.6 in 1907-1909), 3.9 in fallow fields (2.5 in 1907-1909), 2.5 in forest (11.7 in 1907-1909), 1.7 in mixed hav (2.1 in 1907-1909), and 0.7 in wheat fields (1.0 in 1907-1909). In 1907-1909, pastures and oat fields had ahout 1 yellowthroat per 100 acres. The state population of the yellow- throat appeared to change little between 1909 and 1957, either in number or dis- tribution. We estimated that state (sum- mer) populations were about 414,000 birds in 1909 (90 per cent in the southern zone), 362,000 in 1957, and 427,000 in 1958 (80 per cent in the southern zone, both recent census years). House Sparrow.—First successfully introduced into the United States in New York in 1852, the house sparrow was later introduced into other states. At least four introductions were made in Illinois in the period 1868-1876 (Barrows 1889:19). By 1886, virtually the entire state of Illi- nois, as well as a large part of the rest of the United States, was occupied by this species. The urban areas of the country were ideal for the introduced species, and the house sparrow spread through this habitat very rapidly. In all census summers, the densities of house sparrow populations in urban and rural Illinois were highest in the central and northern zones, lowest in the south- ern. In rural cropland habitats, densities were conspicuously high (all census years) in the central zone, but in urban residen- tial areas in recent census years the north- ern zone had the highest populations in the state. For example, 1957-1958 popu- lations in red clover fields were 10.9 spar- rows per 100 acres in the northern zone, 51.2 in the central, and 1.2 in the south- ern, but, in urban residential areas, the densities were 434.8 in the northern zone, 378.3 in the central, and 271.0 in the southern. Residential areas are probably the most important habitat for the house sparrow, but few Illinois species have a more cos- mopolitan distribution. Only from for- ests is this sparrow largely absent. Popu- lation densities of the house sparrow in important summer habitats in the state in 1957-1958 were 373.7 birds per 100 acres in residential areas (265.2 in 1907- 1909), 195.2 in edge shrubs, 56.4 in un- grazed (largelv roadside) grassland, 46.1 in orchards (125.5 in 1907-1909), 31.8 in pastures (21.5 in 1907-1909), 22.0 in oats (9.7 in 1907-1909), 20.7 in red clo- ver (11.7 in 1907-1909), 13.1 in alfalfa, 12.3 in mixed hav (16.7 in 1907-1909), 4.8 in corn (4.6 in 1907-1909), 4.2 in sovbeans, 3.4 in fallow fields (32.2 in 1907-1909), 3.2 in wheat (29.5 in 1907- 1909), and 0.1 in forest (2.2 in 1907- 1909). In most summer habitats, population densities of the house sparrow in recent census years were higher than those in 1907-1909. Notable exceptions were or- chard, fallow fields, and wheat. House sparrow populations in most habitats de- clined in the southern and increased in the northern zones, and both the density increase of house sparrow populations in oats (a northern zone crop) and the de- crease in wheat (a southern zone crop) were probably related to a general north- ward shift in the population. Despite population increases of the house sparrow in certain habitats, the statewide popula- tions of 1957—1958 were not much greater than that of 1909. We estimated that the state June populations of house sparrows numbered about 5,300,000 birds in 1909 (probably about the same in 1907), 6,- 150,000 in 1957, and 5,500,000 in 1958. The number of immatures in these popu- lations is unknown. Urban populations of house sparrows were much greater in 1957-1958 than in 1907-1909, but rural populations, particularly in the southern zone, probably were lower ; so the net change for the whole state was not great. Rand (1956:69-70) and others pointed out the probable importance of domestic livestock in the ecology of the house spar- row and suggested that house sparrow populations in cities declined in recent dec- ades because of the disappearance of horses from the streets. Rand also noted that sparrow populations were more dense in suburban areas than in the business dis- tricts of a large city. Obviously, some prime sparrow habitat is being lost as resi- dential areas near the center of the city give way to the business district, but the net change is toward great expansion of good sparrow habitat. The Illinois popu- lation of house sparrows will almost cer- tainly increase in the coming decades. October, 1963 Grarer & Graber: Bird Populations in I Illinois 489 House sparrow populations in open- field habitats (all census years) declined from an average of about 18 per 100 acres in summer to about 3 in winter. Winter brought no conspicuous increase in spar- row numbers in shrub or forest habitat ; most of the sparrow population wintered in farmyards and urban areas. There is a parallel situation in the introduced mam- mal, the house mouse, which in spring ex- pands its habitat to open fields and with- draws in fall and winter to human habi- tations. Because we had inadequate data for residential habitats in winter, we could not estimate the state populations of the house sparrow for this season. Bobolink.— In the summer surveys (all years), the bobolink was encountered in both northern and central Illinois, but most of the state population was in the northern zone. Though the principal summer habitats, hayfields (all types), oats, pastures, and ungrazed grassland, were well represented in the central zone, population densities of the bobolink in this zone were consistently below those in the northern. In mixed hay, for example, there were about 60 bobolinks per 100 acres in northern Illinois, but only 11 in the central zone. Population densities of the bobolink in various summer habitats of the northern zone in 1957-1958 were 62.1 birds per 100 acres in mixed hav (53.1 in 1909), 52.9 in oats (3.7 in 1909), 44.3 in alfalfa, 38.1 in red clover (18.0 in 1909), 13.6 in pastures (5.2 in 1909), and 5.2 in ungrazed grassland (54.1 in 1909). The relatively dry margins of marshes were probably a favored habitat in 1909 (88 bobolinks per 100 acres). The apparent increased use of oat fields by the bobolink (a change that can be seen in other prairie species) helped to balance the loss in acre- age of ungrazed grassland (a favored bob- olink habitat in 1907-1909) and pasture- land. We estimated that the June popula- tions of bobolinks in Illinois were 1,175,- 000 birds in 1909. 1,860,000 in 1957, and 1,360,000 in 1958. In the central zone, the population increased from less than 15,000 birds in 1909 to more than 100,000 in 1957-1958. The statewide increase fits a pattern of population increase and range extension that is observable in several spe- cies of open-field Icteridae. Meadowlarks,—In all census years, meadowlarks were encountered through- out the state in both summer and winter, but, because of difficulty in determining the species of nonsinging meadowlarks, we do not know the relative proportions of the eastern and western species. Our data represent both species, at least in the north- ern and central zones. All meadowlarks in the southern zone in summer, as far as we could determine, were of the eastern species. Though specimens were taken in Illinois at least as early as 1876 (Allen 1880:54), the western meadowlark was not sufficientlv common to be recorded in the 1907-1909 surveys. In the past 50 years the western meadowlark has greatly extended its range and is now common in both the northern and central zones of Illinois. In most summer habitats, meadowlark populations were more dense in the south- ern than in the northern zone (all census years) ; after 1909, populations in the northern zone increased in most habitats. For example, in red clover fields, popula- tion densities were, for the northern zone, 29.0 meadowlarks per 100 acres in 1957- 1958 (9.0 in 1909) ; for the central zone, 47.8 in 1957-1958 (17.1 in 1907-1909); and, for the southern zone, 49.7 in 1957- 1958 (39.5 in 1907-1909). The fact that meadowlark populations in the northern zone increased suggests that the western meadowlark may have been the species that particularly increased in numbers. In a few habitats, meadowlark populations in the southern zone decreased between 1909 and 1957. In ungrazed grasslands or prairie, for instance, meadowlark popu- lations in the southern zone declined from about 63 birds per 100 acres in 1907-1909 to 50 per 100 acres in 1957-1958, even though in the northern zone populations increased from about 47 birds per 100 acres in 1909 to 80 per 100 acres in 1957-1958. Though the meadowlarks were found (all census years) in all habitats except urban, the most important meadowlark habitats were grasslands and ha\ fields of all kinds. Summer population densities of the meadowlarks in various habitats of the state in 1957-1958 were 58.0 birds per 100 acres in ungrazed grasslands (63.4 in 1907-1909), 48.2 in sweet clover, 44.2 in 490 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 alfalfa. 43.2 in mixed hav (44.H in I9U7- lOOQ), 42.1 in pa>turc (23.5 in 1907- 1909), 41.1 in red clover (30.9 in 1907- 1009). 20.0 in edge shrubs. 17.9 in fallow fields (45.7 in 1907-1909). 8.0 in oats (6.3 in 1907-1909), 7.1 in marsh (10.4 in 1907-1909), 5.8 in orchards (15.4 in 1907-1909). 4.2 in wheat (9.8 in 1907- 1909). 2.7 in corn (1.9 in 1907-1909), and 2.2> in soybeans. Mradowlark population densities in the several hay crops varied considerably from summer to summer (from as low as 20 birds per 100 acres in one year to as high as 50 the next year in a given crop, such as red clover), but the total number of meadowlarks in all hay crops combined tended to remain fairly constant from summer to summer. These data suggest that in the meadowlarks there may be considerable switching of habitat from one year to the next. In some places, in hay crops of the northern zone, particularly, the density of the meadowlark population in a given crop appeared to vary inversely with density of the redwinged blackbird population. We suspect that the meadow- larks and the redwing were reacting to something in the environment other than each other, but the relationship between them needs to be studied along with their specific habitat preferences. The state population of the meadow- larks in fune. b\ our estimates, numbered 4,760,000 in 1909; in 1907, the popula- tion may have been as low as 3,200,000. The estimates iov both 1957 and 1958 were 3,800,000. The size of the state population may not have changed greatly between census periods, but the distribu- tion of the population changed consider- abl\-. In June, 1909, there were only about 680,000 meadowlarks in the north- ern zone of the state, in contrast to 1,100,- 000 in both 1957 and 1958. The southern zone had about 2,000,000 in 1907, 3.100.- 000 in 1909, 1,900,000 in 1957, and 1,- 600,000 in 1958. The data suggest that the northern population of meadowlarks increased and that the southern population ma\ have declined somewhat. B\ winter in all census years, the mead- owlark population had shifted southward, and the bulk of the state population was in the southern zone. Favorite winter habitats of the meadowlarks were hand- picked (cornstalk) cornfields (1906-07 only), hay fields of various types, small grain stubble, and mechanicallv picked cornfields (1956-1958 only). In 1906-07 particularly, the northern and the central zones of Illinois had al- most negligible wintering populations of meadowlarks (probably fewer than 10,- 000). In the recent census years, mead- owlarks wintered farther north in larger numbers; in January, 1957, there were probably about 300,000 in the northern and central zones combined. By our esti- mates, the southern zone had January populations of about 3,100,000 meadow- larks in 1907 and 3,400,000 in 1957. Like a number of other species, in late winter the meadowlarks probably move farther to the south before they move north to their breeding grounds. In February, 1958, the central and northern zones prob- ably had fewer than 10,000 meadowlarks, and the population in the southern zone was down to 1,400,000 birds, concen- trated primarily in hayfields that pro- vided good cover. Redwinged Blackbird.—Few species have undergone a more spectacular popu- lation increase since the turn of the cen- tury than the redwinged blackbird. The redwing was common even in 1907—1909, and the species was recorded throughout the state in all census years. In summer, densities of redwing populations varied from zone to zone and in most habitats were highest in the northern zone (all census years). In 1957-1958, densities in mixed hay decreased from north to south (northern zone: 198.7 redwings per 100 acres; central: 87.4; southern: 53.1). The redwinged blackbird was observed in a variety of summer habitats (all census years) including marshes, drainage ditches, all types of hay crops, all types of grass- land, fallow fields, oats, wheat, corn, soy- beans, plowed ground, shrubbery of all types, orchards, and forest; marsh, edge shrub, sweet clover, and mixed hay were notable favorites. The redwing was pri- marily a marsh species originally; even in 1957-1958, population densities were higher in marshland than in any other major habitat. Long before the first sur- veys, marshland was a disappearing habi- tat in Illinois, and the redwing in this state has made greater and greater use of Ootuber, 1953 (iRAiii'U ^^ (jRahkr: Bird Pohui.ations in Illinois 491 cultivated lands. Between 1907-1909 and 1957-1958, while marshland acreage in Illinois dwindled from about 600,000 acres to 60,000, population densities of the redwing in mixed ha\ increased from about 14 per 100 acres to over 130. Summer population densities of the red- wing in important habitats of the state in 1957-195(S were 300.8 in marshes (309.8 in 1907-1909), 341.7 in edge shrubs, 203.6 in sweet clover, 158.0 along drain- age ditches, 134.3 in mixed hav (14.1 in 1907-1909), 88.5 in red clover (16.1 in 1907-1909), 64.5 in oat Helds (3.9 in 1907-1909), 63.7 in ungrazed grasslands (47.6 in 1907-1909), 57.8 in alfalfa, 30.1 in wheat (6.5 in 1907-1909), 26.5 in fal- low fields {33 in 1907-1909), 23.5 in pastureland (6.0 in 1907-1909), 23.0 in shrub-grown areas, 4.6 in cornfields (1.6 in 1 907-1 9fJ9), and 33 in soybeans. In June, 1909, there were, by our esti- mate, about 5,100,000 redwinged black- birds in the state; the 1907 population may have been as low as 4,000,000. In lune, 1957, the state population numbered kbout 8,400,000 and, in June of the fol- lowing year, over 11,000,000. In 1907- 1909, the distribution of the state redwing population followed the distribution of marshland (high in the northern zone, low in the southern zone) ; marsh habitat accounted for about 60 per cent of the state population. In 1909, in the southern zone, where marshes were least abundant, the redwnng population (about 700,000 birds, in contrast to 2,400, OfJO in the northern zone) w^as already largely in cul- tivated habitats. In 1957-1958, marshes accounted for less than 3 per cent of the state redwing population, and the species had become more uniformly distributed in the state. The redwing is an example of a specie^ that has adapted to a changing environ- ment. While hayfield populations of the redwing have not attained such high den- sities as marsh populations, the hayfields in recent years accounted for most of the state population. Although ha\Helds are the most important nesting habitats, the great increase of redwings in oat and wheat fields should be noted. Small grain fields have been only marginal nesting habitats, but they are probably important foraging habitats. Redwing populations in the state are probably still expanding, and efforts to control "blackbirds" because of their depredations on grain are expected to increase. The redwinged blackbird was not re- corded anywhere in the state in the winter survey of 1906-07. In the recent census years, the winter redwing populations in the northern and central zones of Illinois were all but negligible (fewer than 10,- 000 birds) ; in the southern zone, the spe- cies was common but it was spottily dis- tributed. Favored winter habitats were cornfields, shrubbery of all types, and pas- ture. In January, 1957, we estimated, there were about 5,200,000 redwings in the southern zone. This great increase in the wintering population reflected the gen- eral increase, alread\ noted, and probably also a tendency in the species (as noted in other species) to extend its winter range northward. The great disparity in red- wing numbers between the southern zone and the central and northern zones im- plies that the winter range of the red- winged blackbird cannot expand much north of 39 degrees latitude without a change in climate. Orchard Oriole.—The orchard oriole was found throughout the state in summer (all census years), but it was sighted four times as fret]uentl\' in the southern as in the central zone and was least comm.on in the northern zone. During the course of the censuses, this species was found in pas- tureland, fallow fields, mixed hay, red clo- ver, wheat fields, cornfields, and forest, besides the favorite habitats: orchards, shrubber\ of all types, and (in 1907- 1909) residential areas. Because the 1907-1909 samples of woody habitats for the northern and central zones were par- ticularlx small, we placed emphasis on data from the southern zone in considering pop- ulation changes in this species. Densities of orchard oriole p(jpulations in various habitats in the southern zone in 1907-1909 were 42.0 birds per 100 acres in orchards (1.3 in 1957-1958), 18.1 in residential areas, 10.0 in shrub- grown areas (7.1 in 1957-1958), 3.6 in pastures (2.5 in 1957-1958), 2.8 in fal- low fields (0.4 in 1957-1958), and 1.5 in mixed ha> . Hedgerows and edge shrubs, for which we have no 1907-1909 data, were probably the best orchard oriole hab- V)2 li.i.iNois Natlhai. History SuRVtv Hui.i.i:riN \'(>1. 28, Art. .? itats ill 1^'57-1'>5S. with ilciisities of about 20 orioles per 100 acres in the southern zone. In 1057-1^)58. red clover {.^.5 ori- oles per 100 acres) was a favored fora^inji habitat in the southern zone. Orchard oriole populations were proba- bly never very j^rcat in the northern or central zones. In those zones, by our esti- mate, there were at least 50,000 orchard orioles in niarj^inal (nonwood\) habitats in June, 1009, but less than 25,000 in all habitats in 1057 and 1058. June popula- tions of orchard orioles in the southern zone numbered about 375.000 birds in 1007, 415,000 in 1000, 07,000 in 1057, and 65,000 in 1058. Habitat changes, the f^reat losses in orchard acreage particu- larl\, had much to do with the decline in the oriole population, but other factors than acreage changes must have been in- volved in the population decline. The or- chard oriole was apparently much more common in residential areas in 1907-1900 than in recent years. Also, oriole popula- tion densities in orchards declined greatly between 1000 and 1057. Some qualita- tive characteristics of these prime oriole habitats must have changed, and these changes, in turn, had a serious effect on the oriole population. The changing or- chard oriole population is another of the ornithological problems that need further study. Common Grackle.— During the course of the censuses (all years), the grackle was encountered commonly in summer throughout the state but only once in the winter season (southern zone). Population densities (all census \'ears) in most habitats were highest in the northern zone, lowest in the southern. In marshes, for example, densities in both 1007-1000 and 1057-1058 were about 130 grackles per 100 acres in the northern zone but only 11 per 100 acres in the southern. Favorite summer habitats were edge shrubs and hedgerows, marshes, and resi- dential areas, but grackles were found in all of the habitats censused. Densities of grackle populations in various summer habitats of the state in 1057-1058 were 268.5 birds per 100 acres in edge shrubs. 225.2 in hedgerows, 158.0 in drainage ditches, 97.7 in marshes (56.8 in 1007- 1909), 58.7 in residential areas (18.4 in 1007-1000), 33.7 in orchards (27.0 in 1007-1009), 25.6 in ungrazed grasslands (5.3 in 1907-1909), 19.3 in mowed hay, 17.9 in sweet clover, 16.5 in red clover (37.1 in 1907-1909), 15.2 in fallow fields (5.4 in 1907-1909), 12.8 in pastureland (13.2 in 1907-1909), 12.3 in mixed hay (6.0 in 1907-1909), 10.6 in forest (10.2 in 1907-1909), 7.4 in wheat (5.3 in 1907-1909), 6.6 in corn (7.7 in 1907- 1000), 6.2 in shrub-grown areas (1.8 in 1007-1009), 5.7 in oats (7.1 in 1007- 1000), 4.8 in so>beans, and 2.6 in alfalfa. In most habitats, the recent trend was to- ward increased population densities. The orchard populations are of interest, be- cause the grackle is one of the very few species that had orchard populations as dense in 1057-1058 as in 1007-1009. Despite the high population densities of the grackle in certain habitats in recent years, the state population of grackles de- clined slightly between 1909 and 1957, possibly because of habitat changes, par- ticularly loss of marsh and orchard acre- age. We estimated that June populations of grackles in the state were about 4,100,- 000 in 1909 (probably about the same in 1907), 3,600,000 in 1957, and 3,500,000 in 1958. The grackle population of Illi- nois changed in distribution between the two periods. In 1907-1909, grackles were concentrated especially in the northern zone (41 per cent of the state population) and the central zone (37 per cent) but, in recent census years, the central zone had only about 15 per cent of the state popula- tion. The cause of this regional change is not apparent. The increase in urban acre- age should tend to swell the grackle popu- lation, particularly in northern Illinois, where the population density is highest. Brown-Headed Gowbird.—In all census years, the brown-headed cowbird was found throughout the state in sum- mer, but only in recent years and in the southern zone was it found in the winter season. Summer cowbird populations tended (all census years) to be most dense in the northern zone. In 1907-1909, the southern zone had the lowest population densities, but, in the recent census years, the central zone had the lowest densities. The cowbird was encountered in virtu- all\- all of the summer habitats. Densities were highest in edge shrubs, hedgerows, Octubcr, I9b.^ (jrahkr iSl Grauer: Bird Populations in Illinois 493 and shrub-jirown areas, which are proba- bly the principal habitats of the cowbird hosts, but the cowbird appeared to have less marked habitat preferences than most species of Illinois birds. Densities of cow- bird populations in various Illinois habitats in 1957-1958 were 55.5 birds per 100 acres in ed^e shrubs, 30.0 in hedgerows, 17.8 in shrub-c in the central zone. The dickcissel is another species that has adapted well to cultivated habitats that replaced the original prairie. In 1957-1958, dickcissel densities were higher in fields of tame hay (as a group) than in the ungrazed prairie-like situations; total hay acreage increased between the two census periods. Even at the time of the early surveys, the dickcissel population was probably on the increase. American Goldfinch.— In both sum- mer and winter, the American goldfinch was recorded throughout the state. In all census years, populations tended to be most dense in the northern zone. In shrub- grown areas, for example, in the summers of 1957-1958, there were about 46 gold- finches per 100 acres in the northern zone of Illinois, 33 in the central zone, and 5 in the southern. The goldfinch was found in nearly ev- er) summer habitat censused ; shrubber\ of all kinds, orchards, and ungrazed grass- lands were particularly favored. Summer densities of goldfinch populations in vari- ous habitats in the northern zone in 1957- 1958 were 167.5 birds per 100 acres in edge shrubs, 96.2 in orchards, 69.9 in un- grazed grassland, 46.4 in shrub-grown areas (29.1 in 1909), 7.3 in forest, 6.4 in pastures (2.1 in 1907-1909), 6.1 in oat fields (2.1 in 1909), and 4.3 in marshland. Because of the paucity of data on woody habitats in central and northern Illinois for 1907-1909, there is little basis on which to speculate about population changes in this species. Southern Illinois summer populations, at least, were rough- ly comparable in 1907 and 1958 (about 500,000 birds in each year). For the en- tire state, we estimated, the June popula- tions of goldfinches numbered about 880,- 000 birds in 1957 and 1,(J00,000 in 1958. While population densities were consist- ently highest in the north, the southern zone had most of the good goldfinch habi- tat of the state, and therefore a high per- centage (as much as 47 per cent in 1958) of the state population. In winter, highest populations of the goldfinch occurred in forests, shrubs of all types, in pastureland, fallow fields, and ungrazed grassland, and (in 1906-07) cornstalk habitat. No species in Illinois 496 Illinois Natural History Sur\ i;v Bullktin Vol. 28, Art. 3 showed more erratic Huctuations in popu- lation than the goldfinch ; the winter dis- trihution was particularl\- erratic. In the mild winter of 1906-07, there were, by our estimate, at least 1,600,000 jj;old- finches (January, 1907, population) in Illinois, most (about 90 per cent) of them in the northern and central zones. In Jan- uar\, 1957. the state population was the same as in June of that year, or about 900,000 birds, most (about 80 per cent) of them in the southern zone. Savannah Sparrow.— In summer of both census periods, the savannah sparrow- was encountered in the northern and cen- tral zones of Illinois. However, the popu- lation in the central zone in recent census years was sparse. The savannah sparrow in summer was found in grassland habitats of all types, marsh, all hay crops, oat fields, and soy- bean fields; populations were highest (all census years) in pastures and ungrazed grassland. Population densities of the sa- vannah sparrow in various habitats in northern Illinois 1957-1958 were 38.5 birds per 100 acres in mowed hay, 27.8 in shrub-grown areas, 23.5 in ungrazed grassland, 20.8 in pastures (5.7 in 1909), 13.6 in red clover, 13.0 in mixed hay (1.7 in 1909), 4.3 in alfalfa, 3.9 in sweet clo- ver, 2.8 in marsh (5.2 in 1909), and 2.1 in fallow fields (16.5 in 1909). Alfalfa and sweet clover proved to be relatively poor habitats for this ground-nesting spe- cies. The meadow-like marshes that were more numerous in the early survey years than later may have been a fairly im- portant habitat for the savannah sparrow. The savannah sparrow population in the state probably increased somewhat be- tween 1909 and 1957 despite a loss in pas- ture acreage. In June, 1909, there were, we estimated, 160,000 savannah sparrows in the state (about 20,000 in the central zone). In both 1957 and 1958, the June population numbered about 390,000 birds, most in the northern zone. The savannah sparrow greatly increased its population in hay habitats; there was a general increase in population density that may have had no relationship to habitat acreage changes. In winter, the savannah sparrow was recorded only in the recent census years and in southern Illinois, where the popu- lation was all but negligible. Grasshopper Sparrow.— In all cen- sus >ears, the grasshopper sparrow was en- countered in summer throughout the state; population densities were consistently highest in the central zone and lowest in the southern. In red clover fields, there were about 4 grasshopper sparrows per 100 acres in the northern zone, 9 in the j central, and only 2 in the southern. In summer, the grasshopper sparrow oc- curred in all grassland and hay habitats, oat and wheat fields, soybean fields, corn- fields, orchards, and shrub areas. Densi- ties of grasshopper sparrow populations in a the most favored summer habitats in cen- tral Illinois in 1957-1958 were 53.2 birds per 100 acres in sand prairie, 42.5 in mixed hav (16.7 in 1907-1909), 40.9 in alfalfa, 9.3 in pastures (3.4 in 1907-1909), and 8.9 in red clover (19.2 in 1907-1909). Populations of the grasshopper sparrow in fields of small grain changed between 1909 and 1957. In oat fields of the central zone, there were virtuallv no grasshopper sparrows in 1957-1958 (2.8 per 100 acres in 1907-1909) ; in wheat fields of this zone there were 1.6 grasshopper spar- rows per 100 acres in 1957-1958 (1.1 in 1907-1909). Alfalfa, a relatively poor habitat for the savannah sparrow and a number of other grassland species, proved to be a high-density habitat for the grass- hopper sparrow. The grasshopper sparrow is a small spe- cies, and, except for the singing male, in- conspicuous; in all likelihood, our density figures and population estimates are well below the true figures, but suitable for comparison within the study. Our data indicate that the grasshopper sparrow pop- ulation did not change greatly between the two census periods. In June, 1909, we estimated, there were about 500,000 grasshopper sparrows in Illinois. The 1907 population was higher, probably ex- ceeding 700,000 birds. June populations in 1957 and 1958 numbered, respectively, about 700,000 and 850,000 birds. In all years, the central zone had over 50 per cent of the state population; this latitud- inal distribution was particularly marked in 1957-1958, when about 70-80 per cent of the Illinois grasshopper sparrows were in the central zone. The future for this species appears to be reasonably bright. Pasture acreage in Illinois continues to October, 1963 Graber & Graber: Bird Populations in Illinois 497 decline, but hayfields offer a good reservoir habitat. Vesper Sparrow.—In all of the sum- mer censuses, the vesper sparrow^ vv^as found in the northern and central zones and, in 1957, also in the southern zone. About 90 per cent of the state population was in the northern zone. The vesper sparrow was recorded in summer in all grassland and hay habitats, fallow fields, small grain, soybeans, corn, plowed fields, shrubbery of all types, and orchards ; edge shrubs, red clover fields, and shrub-grown areas were particularly favored by this species. Population densi- ties of vesper sparrow populations in vari- ous habitats of the northern zone in 1957- 1958 were 58.6 birds per 100 acres in edge shrub, 14.5 in red clover (8.9 in 1909), 12.4 in shrub-grown areas, 9.4 in ungrazed grassland, 8.8 in mowed hay- fields, 5.8 in alfalfa, 5.7 in pastures (2.6 in 1909), 3.4 in corn (4.7 in 1909), and 2.9 in mixed hay (2.8 in 1909). The preference of the vesper sparrow for red clover was further indicated by the fact that, in the southern zone (the southern edge of the nesting range for this species), this sparrow was found only in red clover. The vesper sparrow, unlike most of the fringillids, occurred with fairly high fre- quency in bare-field habitats, the row crops and plowed fields. Neither the state population of the ves- per sparrow nor its distribution changed greatly between 1909 and 1957. In June, 1909, there were about 250,000 vesper sparrows in Illinois; the state population numbered about 390,000 in 1957 but onlv about 150,000 in 1958. The population of the southern zone probably did not ex- ceed 10,000 birds in any ^^ear. Habitat changes between the two census periods should not have affected the vesper spar- row to any great extent ; although the pasture acreage decreased, there was more red clover in 1957-1958 than in 1907- 1909. Because the vesper sparrow nests in a greater variety of habitats than most of the open-field fringillids, and because it seems to favor even the bare-field habi- tats, it is surprising that this species did not show some gain in population. Other factors than habitat availability may have been responsible for holding the popula- tion at a low level. Lark Sparrow.—In 1907-1909, the lark sparrow was found in all zones, but between 75 and 95 per cent of the state population was in the southern zone. By contrast, in 1957-1958, we recorded lark sparrows only in the central (about 90 per cent of the state population) and in the northern zone. To a large extent, the distribution of the lark sparrow is proba- bly governed by the local distribution of sandy and other poor soils. In the recent surveys, we covered enough ground to be reasonably certain that the lark sparrow population in 1957-1958 in the southern zone was almost negligible by comparison with the 1907-1909 population in that zone. Unlike virtually all of the other spe- cies censused, the lark sparrow showed no very decided habitat preference, perhaps partly because the soil requirement noted above overrides the vegetation require- ment and partly because this sparrow nests in a broad variety of habitats, both on the ground and in trees. Population densities of the lark sparrow in various summer habitats in the southern zone for 1907-1909 were 4.1 birds per 100 acres in pastures, 2.5 in fallow fields, 2.2 in cornfields, 2.0 in wheat, and 1.6 in oats. Densities in various habitats (sandy and poor soil areas only) in central Illinois in 1957-1958 were 25.2 lark sparrows per 100 acres in hedgerows, 14.3 in plowed fields, 5.5 in fallow fields, 2.0 in shrub- grown areas, and 1.2 in pastures. In June, 1909, by our estimate, there were about 500,000 lark sparrows in Illi- nois, of which 370,000 were in the south- ern zone. The 1907 population was lower, but it exceeded 300,000 birds. Summer populations numbered about 80,000 birds in 1957 and 70,000 in 1958, most of which were in the central zone. The lark sparrow is a versatile species in its nest- ing habits, and it is difficult to understand why the population declined so much ; the great loss in southern Illinois is particu- larly puzzling. Here we can only point out the need for a detailed study of the biology of the lark sparrow in Illinois. Slate-Colored Junco.—In both sur- vey periods, the slate-colored junco was recorded in winter throughout Illinois, but about 90 per cent of the state popula- tion (all census years) was in the south- 498 Ii.i.iNois Natural History Survey Bulletin Vol. 28, Art. 3 ern zone; the numbers fell off sharply to the north. The junco was found in all of the winter habitats; edge shrubs, hedjje- rows, shrub-firown areas, and (in 1906- 07) orchards had particularly high densi- ties. Of the open-field habitats, fallow fields, ungrazed grasslands, cornfields of all types, and pastures were conspicuous favorites of the junco, January populations of the junco in Illi- nois numbered, bv our estimates, about 5,300,000 birds (4,400,000 in the south- ern zone) in 1907 (verv mild weather) and 6,400,000 (5,900,000 in the southern zone) in 1957. The January population of 1957 was higher in most habitats than that of 1907; the 1957 population in the northern zone especially was high, about six times the 1907 level. These data fit a pattern observable in a number of other species—a trend toward higher winter populations at latitudes farther north in recent years. Published Christmas count records for central Illinois (Anon. 1900- 1960) indicate that winter junco popula- tions were neither unusuallv high nor low in 1906-07, 1956-57, and 1957-58. In February, 1958, the state population ex- ceeded 10,000,000 juncos, and, because in the central zone the population was then almost four times the population in Janu- ary, it was evident that northward migra- tion was in progress, despite the severe weather conditions that prevailed. The high population of juncos in Illinois in February must have included a large num- ber of migrants from wintering grounds south of Illinois. Tree Sparrow.— In all census win- ters, the tree sparrow was found through- out Illinois. Unlike the junco, the tree sparrow was uniformly distributed in the state. The tree sparrow occurred in virtually all of the winter habitats censused ; like the junco, this sparrow especially favored edge shrubs and hedgerows, shrub areas, and, among open-field habitats, fallow fields and corn stubble. In 1906-07, the tree sparrow was much more abundant in corn stubble than in picked corn (corn- stalk) fields; the latter habitat was pre- ferred by most species of winter residents. Examination of Illinois Christmas count data (Anon. 1900-1960) showed that the tree sparrow population was more highly variable than the junco population and that the number of tree sparrows win- tering in Illinois was not unusual in 1906- 07 or in 1957-58, but was abnormally high in 1956-57. The strip census data fit well with this picture. We estimated that January populations of the tree spar- row in Illinois numbered about 1,600.000 in 1907 and 6,900,000 in 1957. The Feb- ruary population in 1958 was about 2,- 000,000 birds, and there was no indication of northward migration within the state, though many migrants could already have moved north of Illinois. Chipping Sparrow.—In 1907-1909, the chipping sparrow was found through- out Illinois in summer; in the later survey period, this species was not recorded in central Illinois, and the population in the other zones was vestigial. Even during the early surveys, the chipping sparrow population was highly variable from zone to zone and from year to year ; the south- ern zone had the highest population. In 1957-1958, most of the Illinois chipping sparrows were in the northern zone. Favorite summer habitats of the chip- ping sparrow were residential areas, or- chards, and pastures; in 1907-1909, the chipping sparrow was found in a variety of woody and open-field habitats. In the half century between survey periods, chip- ping sparrows were probably not very abundant in Illinois, but the June popu- lation numbered, bv our estimates, about 250,000 birds in 1909 (probably almost as many in 1907) and less than 50,000 in 1957 and 1958. Habita;t acreage changes may have had little to do with the decline. Loss of orchards would seem to have been detrimental to the chipping sparrow. An- other favorite habitat, residential areas, increased in acreage with no apparent benefit to the species. Field Sparrow.—In all census years, the field sparrow was found throughout the state in summer and in the southern zone in winter. Summer populations tended to be most dense in the southern and central zones, the zones that had the bulk of the optimum habitat ; in all years, most of the state population was in the southern zone. Favorite summer habitats for the field sparrow were shrubs of all types, hedge- rows, orchards, and pastures. Densities of October, 1963 Graber & Graber: Bird Populations ix Illinois 499 field sparrow populations in various habi- tats in the southern zone in 1957-1958 were 200.0 per 100 acres in edge shrubs, 91.3 in hedgerows, 53.4 along drainage ditches, 37.4 in shrub-grown areas (46.9 in 1907-1909), 23.1 in orchards (59.7 in 1907-1909), 19.9 in pastures (8.6 in 1907-1909), 11.7 in fallow fields (8.8 in 1907-1909), 10.2 in ungrazed grasslands, 4.7 in forest (28.4 in 1907-1909), 4.4 in wheat (3.5 in 1907-1909), and 1.5 in hayfields of all types (3.0 in 1907-1909). Although many of the density figures indi- cated higher populations for the early than for the later census years, the density in pastureland, a declining habitat, was nota- bly higher for 1957-1958 than for 1907- 1909. In June, 1909, the state population of field sparrows numbered, by our estimate, at least 2,100,000 birds (75 per cent in the southern zone) ; the 1907 population was lower but probably exceeded 1,700,- 000 (these estimates do not include edge shrub or hedge populations). June popu- lations in 1957 and 1958 were, respec- tively, about 1,400,000 and 1,000,000 birds (62 per cent in the southern zone, both years). Habitat acreage changes probably had some effect on the field sparrow popula- tion. In the summers of 1907 and 1909, southern Illinois orchards alone accounted for over 100,000 birds, in contrast to 15,- 000 or less in 1957-1958. This change represents both an acreage loss and a loss in population density of the field sparrow in orchards. Though several insectivorous and frugivorous species showed density re- ductions in orchards between 1909 and 1957, the field sparrow is one of the few fringillids that declined in orchard habi- tat. The increase in forest and shrub acre- age between 1909 and 1957 would have helped the field sparrow population if pop- ulation density had kept pace with the acreage increase in these favorable habi- tats. Winter habitats for the field sparrow were the winter counterparts of the sum- mer habitats in southern Illinois. The winter population of the field sparrow in Illinois has probably never been very large. We estimated January populations of this sparrow to be about 85,000 birds in 1907 and 190,000 in 1957. The population in February, 1958, was almost negligible (about 10,000 birds), and there was no indication of northward migration. Field sparrows, like birds of a number of other species, probably drifted farther south- ward in late winter. Song Sparrow.— In the recent sur- veys, the song sparrow was found through- out Illinois in both summer and winter. In 1907-1909, the species was widely dis- tributed in winter, but it did not occur in the southern zone in summer. In all census summers, the song sparrow popula- tion was most dense in the northern zone. In shrub areas, the northern zone had about 37 song sparrows per 100 acres, while the central zone had only 8 per 100 acres; the southern zone had only a negli- gible population. Densities of song spar- row populations in various habitats in the northern zone in the summers of 1957- 1958 were 95.9 birds per 100 acres in edge shrubs, 62.9 in hedgerows, 37.1 in shrub- grown areas, 32.0 along drainage ditches, 11.4 in marshes (5.2 in 1909), 11.0 in or- chards, 5,2 in ungrazed grasslands (20.3 in 1909), 3.9 in sweet clover, 3.2 in pas- tures, 2.7 in red clover, 1.7 in forest, and 1.4 in mixed hay (2.8 in 1909). Along with its range extension southward, the song sparrow population in Illinois prob- ably increased at least slightly between 1909 and 1957. By our estimate, June populations of the song sparrow in Illinois numbered about 180,000 birds in 1909, 250,000 in 1957, and 290,000 in 1958. At least 2,000,000 acres of Illinois land were not accounted for in these estimates, and this acreage—probably various mar- ginal habitats—may include a significant amount of prime song sparrow habitat. Thus, the actual state population may be much higher than our estimates for this species. Habitat acreage changes between the two census periods had only slight ef- fect on the song sparrow population. Loss of marshland, orchards, and pasture was largely balanced by increase in forest edge. In winter, though song sparrows oc- curred throughout Illinois (all census years), most of the state population was in the southern zone, where the winter population exceeded the summer popula- tion. Ungrazed grasslands, shrub habitats, marshes, and drainage ditches were espe- 500 Illinois Natural History Survey Bulletin Vol. 28, Art. .3 ciall_\' preferred winter habitats of the son;: sparrow. By our estimates, January populations of son^ sparrows in Illinois numbered about 350,000 birds in 1907 (S8 per cent in the southern zone) and 475,- 000 in 1957 (70 per cent in the southern zone). Like many other species, the song sparrow may be winterinji farther north in jireater numbers now than in earlier years. This sparrow may be more tolerant of cold than many other migratory fringil- lids. As many as 70,000 song sparrows wintered in the northern zone, and, un- like the birds of many of the species con- sidered in this report, song sparrows did not appear to move southward in late win- ter shortly before the onset of spring mi- gration. Our data indicate that, despite severe winter weather, song sparrows were migrating north in great numbers in February, 1958, when the southern popu- lation was swelled to about 900,000 birds, presumably by an influx of migrants from farther south. Lapland Longspur.—In the first win- ter survey- (1906-07), the Lapland long- spur was found only in the northern zone of Illinois, but, in 1956-57, this species was abundant in both the northern and central zones; in 1957-58, it was recorded throughout the state. In recent census years, January population densities were highest in the central zone. Like the horned lark, the Lapland long- spur in winter particularly favored open habitats with relatively little cover; ap- parently some low cover was important in the habitat. In the central zone, popula- tion densities in recent census years were about 84 birds per 100 acres in cornfields, 51 in alfalfa, 42 in soybean stubble, and 28 in small grain stubble, but only 5 in plowed fields. In January, 1907, by our estimate, there were about 700,000 longspurs in Illinois, all in the northern zone. In Jan- uary, 1957, the state population numbered about 4,800,000 birds, most of them (86 per cent) in the central zone and none in the southern. Longspur populations are known to be extremely variable, and per- haps the great difference between the 1907 and 1957 populations falls within the range of "normal" year-to-year variation. Both winters were mild, at least until late January. In recent years (1956-1962), we ha\e found the longspur to be common in central Illinois every winter, and it is possible that the species is extending its winter range southward, or perhaps east- ward. Habitat changes probably favored such an extension. Cornfields, which now make up a large part of the Lapland long- spur habitat in winter, were of little value to the longspur in earlier times when hand- harvesting methods left stalks standing ; the cover was too dense and tall for this species. The initiation of mechanical har- vesting methods, which flatten stalks to the ground, and the beginning of soybean agriculture created millions of acres of prime winter habitat for the longspur in Illinois. In February, 1958, longspur distribu- tion in the state had a pattern not seen previously. In this time of extremely ad- verse weather conditions, longspurs (prob- ably about 5,700,000) occurred through- out the state, but in greatest numbers in the southern zone (about 3,200,000). Coincident with a great increase in the population of the southern zone, the num- ber of longspurs in central Illinois fell from the January level of 4,150,000 to about 1,900,000. Obviously, the popula- tion had shifted southward in late winter, but whether this is an annual occurrence remains to be determined. DISCUSSION Much of the world's ornithological lit- erature deals expressly with variations in populations of wild birds, but still we know relatively little about rates of change in these populations. We know that, in time, even the species is transient; examining the fossil record (Wetmore 1940), we find no positive evidence that any North American bird species now extant has survived more than about 10,- 000,000 years. In less time—since the be- ginning of the Pleistocene, perhaps a mil- lion years ago—the number of species in the North American avifauna has prob- ably been reduced by about one-fourth. In much less time, many important faunal changes have become matters of historical record. In the Illinois avifauna alone (Smith & Parmalee 1955), we could note the disappearance, within the past 100 years, of at least a dozen species and the October, 1963 Graber & Graber: Bird Populations in Illinois 501 establishment in numbers of half a dozen more. Looking back, we perceive faunal changes and acknowledge that the^' are continuing. The fauna that we study now is an ever-changing heritage from the past. Though in a broad sense evolution has no beginning and no end, it has directions that are affected by factors untold in number. The annual fluctuations that character- ize all bird populations make it particu- larly difficult to identify changes that have direction and relative permanence. Certain faunal changes (for example, range ex- tension by such conspicuous species as the cardinal and the mockingbird) are easily detected even in their early stages. Other faunal changes (for example, the decline leading to extinction of a species) may be noticed only in the later stages of the change. Some trends may be detected only in the light of periodic population meas- urements. The need for detailed censuses of birds was recognized long ago, but, despite the initiation of the Christmas counts in 1900 (Chapman 1900:192), two nationwide summer censuses sponsored by the United States Biological Survey (Cooke 1915, 1916), and subsequent development of a regular program for censusing breeding birds (Hickey 1937), there are still rela- tively few bird population data available for much of North America. Most re- corded population measurements of high quality are provincial in avifaunal, eco- logical, and geographical scope and span only relatively short periods of time. In- formation for habitats other than forest is particularly scarce, though the census program is expanding steadily through the voluntary efforts of many ornithologists. The value of systematic bird censuses increases as the years pass, for without some reference to the past we cannot see the trends of evolution ; we can see neither the magnitude nor the direction of change. In terms of quantitative data on bird pop- ulations in North America, we have few reference points before 1915. In view of the paucity of quantitative data, and the habitat changes that have occurred in the past half century, the efforts of Stephen A. Forbes and Alfred O. Gross to provide detailed information on the bird life of 1906-1909 in virtually everv habitat in Illinois appear particularly farseeing and commendable. Almost inevitably, the field biologist, because he deals with many variables, be- comes uneasy about the adequacy of his data. In this paper, our interpretations are based on a record of only 4 years, 2 early in this century and 2 in midcentury. For many species of birds, the temporary' fluctuation in population between two con- secutive census years might far exceed any irreversible directional change that would occur in a period of 50 years or more. Fully recognizing the possibility of con- fusing short-term fluctuations with rela- tively permanent changes, we have still accepted the differences between the 1906- 1909 and 1956-1958 data largely at face value. In our conclusions, we have been guided for the most part by the strip census records. The data presented in tables and text are always open to re- evaluation, and the reader should bear this fact in mind. Events Previous to 1800 Following the last glaciation—perhaps 10,000 years ago (Livesay 1951:23)— and before white settlement, there were probably few types of bird habitats in the area that was to become the state of Illi- nois. In succession, the melting glaciers gave way to open lakes, to marshes, and then largely to drier habitats of grassland and forest. The present Illinois soil types indicate that in pre-Columbian times and as late as about 1800 approximately 14,- 000,000 acres were forested (King & Winters 1952:20) and between 21,000.- 000 and 22,000,000 acres were primarily prairie grassland. Included in these total acreages there were probably more than the 1,400,000 acres of wetlands reported by Shaw & Fredine (1956:5) for a later period. Naturally disturbed forest areas (areas disturbed by fire, flood, or erosion) undoubtedly gave rise to some shrub habi- tat, but the acreage of this habitat is in- estimable. Quantitatively, at least, the Illinois avi- fauna of 1800 and before is unknown. If we could assume bird population densities for 1800 similar to those of the early 1900's for the acreages in the primary habitats of forest, marsh, and prairie, then in 1800 and probably many years before 502 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 the Illinois area would have had a breed- ing bird population of about 97,000,000 birds—53,000.000 in forest, 7,500,000 in marsh, and 37,000,000 on the prairie. In the years previous to 1800, man was a minor force in effecting faunal changes in the Illinois country. The Indian inhabi- tants of this area cultivated some land, probably only a few thousand acres. Mar- quette reported that the Illini tribes num- bered 8,000 or 9,000 persons in 1670 (Temple 1958:14). The Indian popula- tion of the area dwindled through the 18th century. Zebulon M. Pike reported that in 1805 the Sauks and Foxes, who had largely replaced the Illinois tribes, together numbered onlv about 4,600 per- sons (Temple 1958:99-101). These thin populations had probably transformed but little of the natural habitats of the area. Development of Managed Habitats White settlement of the Illinois coun- try, which began about 1700 (King & Winters 1952:10), was still negligible bv 1800. In 1798, there were about 5,500 whites in the area that later formed the states of Illinois, Indiana, Wisconsin, and Michigan (Hagan 1958:3). In the fol- lowing century, the 19th, most of the Illi- nois lands came under cultivation. In that century, perhaps as many as 10,000,000 acres of forest were removed. If our hypo- thetical estimate of the bird population of 1800 was correct, the decimation of Illi- nois forests in approximately 100 years was tantamount to the elimination of about 38,000,000 breeding birds from the state. Hicks (1935:306) suggested that the orginal forest in eastern North Amer- ica, because it offered relatively little edge, may have been poor bird habitat. Even if it was poor habitat and our estimate for 1800 was considerably high, 19th century deforestation must have taken a tremen- dous toll of Illinois birds. Areas adjacent to the Illinois country were also coming under the plow, and forests that remained must have been quickly populated to satu- ration. In the 19th century, also, grassland and marsh habitats were being transformed. Bv 1830, Illinois had nearlv 160,000 whites (Anon. 1832:38). By 1850, it had 12,000,000 acres in farmland (Anon. 1936:151 ) ; the farm acreage almost dou- bled in the next decade and reached about 33,000,000 by 1900. The acreage of corn, oats, and cultivated hay more than dou- bled between 1866 and 1900 (Anon. 1936:153, 155, 165), supplanting most of what remained of the original 36,000,000 acres of natural habitats. What was left by 1900 was about 3,500,000 to 4,000,000 acres of forest (some of it grazed), about a million acres of prairie grasslands and marsh combined, and a vast expanse of land in various stages of cultivation. Most of the cultivated habitats, new to Illinois, were without an avifauna. Some prairie species held on in marginal prairie acre- age, and for a number of prairie birds there was probably little hardship in the transition from wild prairie to tame or cultivated hay, or to pastureland that was not overgrazed. In 1900, the row crops, plowed fields, and small grain fields, which occupied nearly 20,000,000 acres, were for breeding birds largely a void to be partially filled later by the horned lark. Particularly in southern Illinois, de- forested areas that did not come immedi- ately under cultivation were quickly oc- cupied by a shrub flora and avifauna. The century that saw the Illinois forests deci- mated brought approximately 300,000 acres of orchards into being, and, between the marginal forest species and the mar- ginal prairie species of birds, the orchards had a ready-made avifauna. In that cen- turv, too, a notable acreage (probablv about 350,000 acres by 1900) of human residential habitat developed in Illinois. Much of it rural and adjacent to orchards, residential habitat usually had tree and shrub cover of its own that claimed some segments of the forest and shrub avi- faunas. By 1900, over much of Illinois and the Midwest, there was beginning to be an agriculture-adapted avifauna. The trends of change were established, and the ensu- ing 60 years saw them continued. As in previous times, some species adapted to the change. In a few cases, man unwittingly adapted the environment to suit the species. The past 150 years in Illinois have seen the beginning and development of a spe- cialized kind of evolution. Albeit unwit- ting, it is, nonetheless, evolution by man- agement. The pattern of change is not October, 1963 Graber & Graber: Bird Populations ix Illinois 503 basically different from that in previous times, when other species of animals probably "guided" evolution to some ex- tent, though the rate of change may never before have been so fast. In little more than 100 years, the Illi- nois landscape changed immensely, from a few^ relatively high density habitats with an estimated June population (primarily nesting adults) possibly as high as 97,000,- 000 birds in 1800 to the diversified, man- aged habitats of 1907, which supported about 61,000,000 birds. In the next half century, the state avian population changed but little in total number. There is more to the picture of changing bird populations in Illinois than these gross population figures can tell. None of the population changes, of course, represented a general decrease or a general increase in the whole population. Of the 40 most abundant species of birds in the state, 17 showed notable population increases in the half century, 17 showed decreases, and 6 had about the same populations in 1907- 1909 as in 1957-1958. There was selec- tion, adaptation, extirpation ; in short, there was evolution continuing. If we emphasize the changes of the half century between the two surveys, it is only because of the temporal limits of our data, for the patterns of change that led into the 19th century are continuing still. Specific Changes in Avifauna The basic patterns of change in the Illinois avifauna during the five decades between the two surveys can best be pre- sented by example. For many of the changes observed we can offer no explana- tion, and, in all cases, the reader should bear in mind that it is easy to oversimplify so complex a phenomenon as evolution. Unless otherwise stated, the population figures presented represent June popula- tions, primarily the adult nesting popu- tions. Earlier, we noted that there was no ready-made avifauna for most of the newly developing, managed habitats of 19th cen- tury Illinois. An increasingly greater use of some of these habitats by certain species of birds, both exotic and native, was a dominant trend of many decades. A case in point was the utilization of residential habitat by exotic species. Intro- duced species thrive in managed habitats, and arrival of the house sparrow on the continent could not have been timed much better to take advantage of the swelling acreage of residential habitat. In 1907- 1909, the house sparrow was already a part of the Illinois avifauna, and was, in fact, probably the most abundant species in the state, with a population of at least 5,300,000 birds. The sparrow population was only slightly higher in 1957-1958 than in 1907-1909; in the intervening years, the house sparrow, like man, had become increasingly urban in distribution. The starling, which was not even present in the state until about 1926, well after the early surveys, attained by 1957-1958 a state breeding population of at least 3,- 100,000 birds, most of them in residential areas. What efifect the starlings had on other cavity-nesting species can only be sur- mised. At least partly coincidental with increasingly greater numbers of starlings, flicker populations in the state fell from about 2,300,000 in 1909 to 300,000 in 1957, and the numbers of red-headed woodpeckers declined from 1,300,000 in 1909 to 130,000 in 1958. These native birds are not strictly forest species, but in- habitants of marginal, savanna-type, or even residential habitats, and they almost certainly came into competition with the starling. In recent years, flicker popula- tions in residential habitat were inversely proportional to the starling population, and starling numbers are presumably still increasing. Such native cavity nesters as the red-bellied and hairy woodpeckers, which are more restricted to the natural forest habitat, have not had to compete much with the starling and have shown no population decline. The evidence against the starling, though circumstantial, appears incriminating. During the habitat changes of the 19th and early 20th cen- turies, some native species found a niche in man's residential habitat, but, to the medium-sized cavity nesters in this group, the introduction of the starling was de- structive. These exotic species were adapted to the residential habitat even before their intro- duction into Illinois. Two native species, the chimney swift and purple martin, were probably adapted to the urban situation 504 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 lonj: before 1*^00. From a broad ecolojj;ical background in 1Q07-1W9. the robin pop- ulation in Illinois had. by 1957-1958, come to survive almost entirely in residen- tial habitat. Like the human population, the robin population has been concentrated particularly in northern Illinois. Adaptive utilization of cultivated habi- tats extended to some open-country birds. l\vo examples deserve special discussion here. At least since the time of the early surveys (and presumably in previous a^es). redwinjied blackbird populations have attained their maximum densities in cattail marshes. In 1907-1909, though redwings occurred in prairie, hayfields, and other habitats, most of the state pop- ulation, which numbered about 5,000,000 birds, was in marshland. By 1957, the population numbered over 8,000,000 (11,- 000,000 in 1958), and most of the Illinois population w-as in cultivated habitats, par- ticularly mixed hay. In the period 1907- 1957, marshland, which had been largely restricted to the northern half of the state, dwindled to a tenth of its 1907 acre- age, and sod grasslands gave way increas- ingly to cultivated hay throughout the state. In this more w'idely distributed habitat, the redwnng population swelled. The redwing may be expanding its utiliza- tion of secondary habitats even further. For instance, there is clear indication of increased use by the redwing of small grain fields, a habitat reservoir amounting to several million acres. This trend prom- ises further increase in the redwinged blackbird population. Even more spectacular than the popula- tion increase of the redwinged blackbird was the change in population of the horned lark. Between these two species, there was a subtle, but basic, difference in the mechanism of change. For the red- wing, marshes were, and still are, the fa- vorite habitat (judged from population densities) ; yet the redwing invaded a sec- ondary habitat that by 1957 supported most of the population. F'or the horned lark, man unwittingly created what proved to be an "optim.um" habitat. Be- fore white settlement, the horned lark probabl\- resided in the relatively barren parts of the prairie grassland, and its pop- ulation was probably not very great. The lark avoids tall cover, and bare ground is apparently an important part of its habitat. The great 19th century expansion of agriculture opened a vast land to the lark, \Vith white settlement, increased grazing on the primary grasslands im- proved, for the lark, the original habitat, but even from pastures the lark moved in- creasingly to tilled land. The newly opened habitats were not saturated in 1907-1909 when the Illinois horned lark population was under 1,500,000 birds; bv 1957-1958 there were about 5,000,000 horned larks in the state. For the horned lark, this population change in Illinois was probablv representative of changes in other parts of the Midwest (Hicks 1935:308). Specialization in Managed Habitats The adaptation of bird species to the cultivated scene was but one major force in shaping the present avifauna. The culti- vated habitats themselves became more spe- cialized through changes in management. Here, for one example, we can refer to changes in orchard management to show at least two ways in which bird popula- tions were affected. While the density of the total bird population in orchards was about the same in 1957-1958 as in 1907- 1909, certain species, principally insectiv- orous and frugivorous types such as the eastern kingbird, robin, blue jay, the mim- ids, and orchard oriole, tended to disap- pear from the orchard avifauna. At least some of these species maintained or even increased their population densities in other habitats. Why they should have de- clined in orchard habitat particularly is a problem that needs further study. The in- creased use of insecticides in orchards and the development of organic insecticides may have had some bearing on the change. Much of the orchard acreage in 19th and early 20th century Illinois was composed of noncommercial farmyard orchards that probably received little insecticide spray- ing. Later these farmyard orchards gave way largely to commercial stands that re- ceived regular treatment with insecticides. Both the change in size of individual orchards, from family farm plots to large commerical stands, and the great decline in total acreage of orchards had their ef- fect on the avifauna. The commercial tracts of 1957-1958 had a decidedlv uni- October, 1963 Graber . Pertinent here is the fact that in each of the manajjed hi^h density habitats used as examples above (hay crops and residential areas) part of the bird population was composed of species (purple martin, house sparrow, starling, and redwinj^ed black- bird) that show a Wi^h dej^ree of intra- speciHc tolerance. It is such species, par- ticularly, that increased in population after 1909. We must bear in mind that managed habitats, which have poor a\i- faunal variety, are the expanding habitats. Since the turn of the century, the acreage of cultivated ha>' has grown as the acreage of prairie grasslands has dwindled. The trend toward specialization of habi- tats and their associated avifaunas (elimi- nation of savanna-type habitat was a par- allel trend) tended to reduce the number of bird species that could be classed as common in the state. A reduction in com- mon species has become apparent even since 1909. If we arbitrarily define the common species as those comprising 70 per cent of the state population, we find that there were, in the Illinois avifauna, 18 common species (about 40,000,000 birds) in 1907-1909 and onlv 14 common species (42.500,000 birds) in 1957-1958. Data for 1909 and 1957, the years of best cov- erage, show an even greater difference in avifaunal variety, table 56. Population Changes and Latitude Although specialization of habitats and adaptation by particular species to these habitats were dominant forces of change in shaping the present Illinois avifauna, certain special changes were important enough to deserve elaboration. We noted earlier that a number of species of birds suffered population losses, particularly in the southern zone of the state. No single factor could account for the waning pop- ulations in all of these species. The popu- lations of most of these species had been highest in 1907-1909 in the southern zone, and therefore that was the zone in which they had the most population to lose. Most of these species lost population in other zones, also, but a few—for ex- ample, the catbird and robin—actuallv in- creased their northern populations, while losing in the south. Others lost propor- tionately less in the northern zone than in the southern. The brown thrasher pop- ulation, for example, fell from about 160,- 000 birds (1907-1909) to 130,000 (1957-1958) in the northern zone (about 20 per cent loss), but from 800,000 to 180,000 in the southern zone (about 80 per cent loss). The effect of these specific changes can be seen and expressed in terms of the entire state population of birds, for, between 1909 and 1957, the breeding-bird populations of northern and central Illinois actually increased, while the breeding-bird population in the south- ern zone declined, or, at best, merely held its own. Why, within a species, did the population in the northern zone survive better than that in the southern? This question suggests another group of prob- lems in Illinois ornithology that need fur- ther investigation. It is a mistake to as- sume that all of the species showing decline are responding to the same factors, thougli to some extent they may be. The fact that the population losses varied with latitude suggests the possi- bility of climatic influences on the popu- lations. The continent has probably been in a generally warming trend since the last glaciation ; the temperature climb has been studied in detail since 1885 (Con- over 1953). How, or if, this climatic warming has affected survival of breed- ing birds remains to be determined. Per- tinent here are the notable changes in winter distribution of Illinois birds. Sev- eral species, including the mourning dove, mockingbird, robin, the meadowlarks, red- winged blackbird, swamp sparrow, and song sparrow, either extended their win- ter range northward in the state between 1909 and 1957 or wintered in Illinois in larger numbers in 1957-58 than in 1906- 07. The winter (January) population of birds in Illinois increased from about 30,- 000,000 in 1907 to 55,000,000 in 1957. The factor or factors that effected popu- lation changes in the state winter popula- tion may also have influenced the breed- ing population. Range Extensions Among the types of change in the Illi- nois avifauna between 1909 and 1957, range extensions by a few species deserve October, 1963 Graber & Graber: Bird Populations in Illinois 509 special mention. Of the common species censused, at least seven, all but one pri- marih' southern forest species (turkey vul- ture, red-bellied woodpecker, Acadian fly- catcher, tufted titmouse. Bell's vireo, car- dinal, mockingbird, and probably the Car- olina chickadee), extended their breeding range northward, and four, all icterids (bobolink, western meadowlark, yellow- headed blackbird, and Brewer's black- bird), extended their range southward or southeastward. The larger number of spe- cies moving north than south probably re- flected the fact that deciduous habitat species were more numerous in the south. In addition to the species that made range extensions, there were a few species that greatly increased their breeding popula- tions in one zone particularly. Probably the most notable example was the barn swallow, which enlarged its southern zone population tremendouslv from a verv low level in 1907-1909. In most cases, range extensions occurred from saturation or near-saturation popula- tions in adjacent areas. The red-bellied woodpecker, for instance, was essentially a southern species in 1907-1909, with a saturation population in its primary habi- tat (forest) of about 5 birds per 100 acres. By 1957, this species had attained popula- tions of the same density in the central zone and was still spreading northward, though populations in the northern zone were sparse (1 bird or less per 100 acres). At least two species, the turkey vulture and mockingbird, spread their populations northward despite thinning in the south- ern zone. The range extensions of the several species of icterids mentioned above fit a broad pattern of change. All of these species experienced notable population in- creases between 1909 and 1957; all are marsh-inhabiting or open-field representa- tives of the blackbird family. Such a con- sistent trend toward population increase among the species of one family suggests the possibility of some particular genetic vigor, or at least a genetic unity that makes them all favorably responsive to the changes that man has wrought. The grackle, which qualifies both genetically and ecologically for this group, merely held its own between the two survey pe- riods, but it found a niche in the expand- ing urban habitat and should, in time, in- crease ; the two strictly arboreal members of the family, the orchard oriole and the Baltimore oriole, suffered population de- cline. Habitats and the Future of the Avifauna In a very general way, we have traced the development of our present Illinois avifauna. To know more precisely where the avifauna is in its sequence of develop- ment, and what we might expect in the way of avifaunal changes in the near fu- ture, we need to consider in more detail the relative availability, and the value to birds, of various Illinois habitats. We can evaluate a habitat both in terms of the number of birds it supports and the num- ber of species it supports. If we arrange the habitats according to the number of breeding birds they supported, listing those with highest population densities first, the sequence for 1957-1958 was urban resi- dential areas, marsh, shrub, orchard, hay crops, forest, grassland, oats, wheat, the row crops, and bare-field or plowed ground. The same habitats arranged in order of decreasing avifaunal variety were forest, shrub, orchard, urban residential areas, marsh, grassland, hay crops, oats, wheat, row crops, and bare-field or plowed ground. Row crops comprised over a third of the state acreage in 1957-1958 and are unlikely to diminish in acreage in the fore- seeable future. These crops have some value as foraging habitats for several spe- cies of birds, but there is no indication that species other than the horned lark depend significantly for their survival on this vast acreage. Acreages of small grain crops, particu- larly oats, declined between 1930 and 1957, and most of the lost acreage of these crops went into row crops. The change represents a loss to the Illinois avi- fauna in terms of both numbers of birds and faunal variety. However, no species of bird is now entirely dependent upon the small grain habitats; these habitats form a kind of overflow area for species that usually attain higher population den- sities in hay crops and grassland. If hay and grasslands disappear, part of the avifauna, particularly adaptive species 510 Ii.i.ixois N-ATf RAi. History Survey Bulletin Vol. 28. Art. 3 such as the redwinj;, may survive princi- pally in small ijrain fields. The redwinj: population, already somewhat in need of control, may expand even further in small jjrain habitats; small j^rain acreage in the cominji years should not decline much be- low its present level. Hay crops as a t^roup, because they combine high population densities with large acreage, accounted in 1957-1958 for over 20 per cent of the state bird popula- tion, or at least 13,000,000 birds (in con- trast to 5,000,000 or 6,000,000 in 1907- 1909). In the 100 years before 1957, culti- vated hay was an expanding habitat, re- placing principally wild hay and pasture- land. The change tended to favor a few species, especially the redwinged blackbird and the dickcissel, and to increase the total number of birds in the state, while reducing the variety of common species in the areas in which the change took place. The change is continuing, and pastureland acreage is falling steadily, as livestock is being confined more and more to smaller feedlots. Coincidentally, the hay crops have been made more specialized. Much of the mixed hay acreage has given way to al- falfa, a poorer habitat for some of the prairie birds. In recent years, there has been some experimentation with other types of legume forage plants ; if present hay t^'pes should ever give way to viny legumes, the hayfield avifauna would suf- fer greatly. Prairie marshland, the habitat with the second highest population density of birds, had all but disappeared from the state by 1957-1958 (60,000 acres in contrast to 560,000 in 1907), but it accounted for over a million birds, including a variety of species not adapted to other habitats. In the immediate future, the remnant marshland may be safe, but, as the human population expands and the land available for food production declines, pressure will come for the elimination of marshes and other uncultivated open-field habitats. Marshland acreage could actually be in- creased in the state, especially near large reservoirs. Because of the specialized char- acter of the fauna of marshland, conserva- tionists should encourage both the develop- ment of new marshland areas and the preservation of the existing marshland. The acreage of shrub-grown areas. which in 1957-1958 accounted for at least 2,000,000 birds in the state, probably increased slightly between 1909 and 1957, but it may decline seriously in the com- ing decades. Land-use patterns over most of the state are more stabilized now than they were even 50 years ago. Most shrub- grown habitat constitutes a transitional habitat that usually gives way to forest and depends on change of one sort or an- other for its continued existence. Areas now in shrubs are growing into forest, and the principal sources of shrub land (deforestation as it was formerly prac- ticed and retirement of cultivated fields) have been largely cut ofi. Forest will con- tinue to be harvested, but the harvest methods now most widely used (not the same as when trees were removed over great tracts of land) do not lead to shrub land. The amount of Illinois shrub land maintained by edaphic or topographic con- ditions is negligible. In addition, the acre- age of edge shrubs (fencerows and road- sides) and hedgerows is rapidly being greatly reduced. Edge shrubs and hedge- rows may have a higher population den- sity of birds than any other habitat in the state, and it is particularly regrettable that these habitats are being removed in an era when there is no shortage of food- producing acreage. Though of very lim- ited acreage (less than 100,000 acres), these edge habitats bring faunal variety to vast areas of open-field habitat where the fauna would otherwise be very limited ; from the standpoint of efficient use of space for increasing populations of native species of birds, probably no easily obtain- able habitat is superior. Fortunately, many shrub-inhabiting spe- cies can survive in forest understory, but there are some, such as the prairie warbler, Traill's flycatcher, and Bachman's spar- row, which require open shrub arrange- ments; few^ shrub-dwelling species attain such high population densities in forest as in shrub-grown areas. Shrub habitat, like marsh, is important to the Illinois avi- fauna, both for its high population densi- ties and for the variety of specialized spe- cies it supports. Fortunately, land use in Illinois wmII probably never attain a state of equilibrium that will eliminate shrub- grown areas completely, but the day may come when some acreage will have to be October, 1963 Graber &c Graber: Bird Populations in Illinois 511 managed specifically to create shrub habi- tat in order to maintain an interesting seg- ment of our avifauna. In little more than a century, orchard habitat in Illinois came into existence, ex- panded to an area of over 300,000 acres that supported nearly 2,000,000 breeding birds, and then decreased drastically. To- day, partly because of the limited acreage, the bird population (about 110,000) in orchards of the state is almost negligible and will probably remain so in the coming decades. Forest, the woody habitat with the most varied fauna but lowest population den- sity, will probably continue to increase slightly in acreage in the coming years. This increase will help to increase the state population of birds and maintain the variety of species. Like other natural habi- tats, forest may ultimately be endangered by the swelling human population with its needs for lumber, food, superhighways, dwelling areas, and trading centers. The elm diseases, which have left dead trees in forests throughout much of Illi- nois, have created a special habitat that may for a short time favor population in- creases among certain picids and other cavity-nesting birds. Urban residential areas, which now boast a higher bird population density than any other habitat except edge, occupied an almost inconsequential acreage only 100 years ago. By 1909, urban area in the state was up to 350,000 acres and ac- counted for about 3,000,000 birds (6 per cent of the state population) ; by 1958, the area exceeded 800,000 acres, account- ing for nearly 8,000,000 breeding birds (13 per cent of the state population), and was growing at an ever-increasing rate. The end of this growth is not in sight, and, because urban areas are claiming an increasingly important role in the develop- ment of the Illinois avifauna, this habitat deserves careful and intensive study. Most of the state population of introduced prob- lem species (starling, house sparrow, and rock dove) is produced in residential habi- tat. To some extent, these introduced species are probably effecting limitations on native species in the urban residential avifauna, but, even if the exotic species were not present, the urban fauna would be restricted in variety. The house sparrow population appears to have reached the saturation point, at least in old urban areas, but, because the urban residential habitat is expanding, the sparrow popula- tion will increase. The starling also should continue to increase in numbers; its popu- lation may not yet have reached the sat- uration point in any habitat. To date, conscious efforts to control sparrow and starling populations by planned elimination of their nesting sites have been negligible. The "gingerbread" house and similar architectural patterns of past decades, because they offered a multi- plicity of nesting and roosting sites, were probably especially favorable to the spar- row and starling. Few native species make use of human dwellings; therefore, build- ing design offers an important and specific technique for the control of the three in- troduced problem species. The common practice by realtors of planting fast-grow- ing softwood trees in new housing addi- tions probably favors some native species of birds. The practice also favors the starling. Landscape architecture offers an- other effective avenue of control for prob- lem species. From an economic standpoint it is, of course, not feasible to quickly supplant established housing and land- scape features, but at present the acreage of residential habitat in Illinois is expand- ing greatly, and some effort should be made to at least study the possibilities of planned control of problem bird species by building and landscape design. Residential habitat itself is changing in character. The newly developing large acreage of suburban housing will, for some years, have limited arboreal habitat for birds, and the house sparrow will probably dominate the early stages of suburban birdlife. The absence of large trees in new suburbs and the low-level dimensions of many suburban houses should discourage starlings to some extent in these areas. The bird-attracting poten- tial of new housing and landscape designs remains to be determined. Because of the absence of large trees, grackles, flickers, crested flycatchers, and some of the other prominent species of older residential areas will be largely missing from the suburbs for some time. Developing small trees and shrubbery should favor some native spe- cies. The robin, which seems to have be- 512 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 come dependent on residential habitat, and the mourning do\e should increase their populations. Before 1980, there will probably be over 1,000,000 acres of urban residential habitat in the state, with a bird population numbering over 10,000,000 and including as many as 6,000,000 house sparrows and starlings in this habitat alone. Properly managed, this acreage could be made more pleasant for its human inhabitants and at- tractive to a variety of desirable native species of birds. Urban and suburban busi- ness districts, which are beginning to absorb a significant fraction of the state acreage, represent an almost total loss as habitat for native birds (except night- hawks), but they support large popula- tions of the three introduced species. Road and highway surfaces and rail- road trackage also represent lost habitat acreage for birds. We have estimated that about 600,000 acres of Illinois land were covered b\' road (surfaces onlv) in 1910, and over '1,100,000 in 1960. More acre- age will go under concrete as highways are widened and work on four- to eight- lane interstate routes is expanded. As many as 1,500,00 acres may thus be uti- lized in the state by 1980. Along the margins of this highway system is a grassy roadside cover that in 1960 occupied nearl\" 400,000 acres along primary roads alone. This habitat—useful to a few na- tive species of birds, notably meadowlarks —should increase in acreage in the coming decades, especially along interstate routes. This road-edge habitat warrants special study for its value to birds. An unknown in relation to the expan- sion of these urban and highway areas is where the acres will come from ; that is, what present habitats will be reduced to make room for the expansion ? The proba- bility is that most of the acreage for the expansion will come from open cultivated fields, particularly row crops, which would represent little loss to birds; in some areas, in the southern zone especially, some for- est or shrub acreage may fall to the burgeoning cities and highways, and this would represent a definite loss. The habitat changes discussed above had a profound effect on the Illinois avi- fauna, but it is difficult to understand some of the observed population changes. and probabl\- it is misleading to generalize about them. It is easy to see that the re- duction in acreage of orchards, a habitat notabl\' concentrated in the southern zone, could have reduced the orchard oriole pop- ulation in this zone from about 400,000 birds in 1907-1909 to 100,000 in 1957- 1958. On the other hand, it is difficult to understand why the blue jay population should have lost over half a million birds in the southern zone in a period when wood}' habitats were expanding. It is rea- sonable to assume that the introduction of the starling may have played some role in the decline of such cavity-nesting species as the red-headed woodpecker and flicker and that the expansion of woody habitats had a bearing on the increase in the indigo bunting. But what of the virtual elimina- tion of the lark sparrow, which in 1907- 1909 had a population in the southern zone of at least 300,000 birds? Here, for the most part, we can only point to the population changes ; we cannot explain them. There is room for speculation and there are many factors to consider—cli- matic changes, habitat changes, competi- tion, genetic vigor, and others—but all paths of speculation lead inevitably to more and more questions and the ultimate realization that each of these species needs special, detailed study. We should not for- get, either, that the apparent population changes may represent transient conditions —normal fluctuations or temporary set- backs from which any or all of the species mentioned may come back in force. Among the factors that complicate the interpretation of apparent population change in a given species is a lack of pre- cise information on the relative impor- tance of various habitats to that species. The census data revealed that few species of Illinois birds spend the day solely in only one or two habitats. Even some for- est species spend time in open fields, figs. 31 and 32. We have hypothesized that the high bird population of a few relatively stable natural habitats characteristic of primitive Illinois declined in the 19th and early 20th centuries as the natural cover gave way to the agricultural and other man- aged habitats that came with white settle- ment and that, although for most of these new Illinois habitats there was no real October, 1963 Graber & Graber: Bird Populations in Illinois 513 avifauna, an agriculture-adapted avifauna was probably beginning to develop even as agriculture came to dominate the land. When the Illinois bird population reached its low we cannot say; by 1907— 1909, at a level of 61,000,000 birds, it may have been climbing. In the next 50 years, despite waning populations in a number of species, especially inhabitants of savanna-type areas, the total Illinois bird population remained about the same, principally because of a new introduction, the starling, and expanding populations in the relatively few species that comprised the avifauna for managed habitats. Be- cause of these species the state population will probably increase in the coming dec- ades. Even the redwing and horned lark populations have probably not yet reached saturation levels, and there may ultimately be increased use of croplands by a few other species. Our prognostication that the number of birds in Illinois will increase in coming decades is based primarily on a considera- tion of changes in habitat and the response of a few species to these changes. In truth, we do not even begin to know all of the factors that will affect future populations of Illinois birds. SPECIES HORNED LARK KILLDEER SAVANNAH SPARROW MEAD0WLARK5 BOB WHITE BARN SWALLOW BARE FIELD PASTURE, GRASSLAND HAY, CLOVER SMALL MARSH SHRUB, pqrest URBAN GRAIN ORCHARD RESIDENTIAL UPLAND PLOVER GRASSHOPPER SPARROW- BOBOLINK DICKCISSEL VESPER SPARROW- CHICKADEES- MOCKINGBIRD- TOWHEE ORCHARD ORIOLE- CHAT YELLOW-B. CUCKOO- FIELD SPARROW INDIGO BUNTING YELLOW THROAT BLUEBIRD GOLDFINCH CATBIRD CARDINAL BROWN THRASHER- CRESTED FLYCATCHER DOWNY WOODPECKER 1- TUFTED TITMOUSE BLUE JAY J- RED-H WOODPECKER h PURPLE MARTIN- HOUSE WREN STARLING 25 ,10, 50 100 PER CENT SCALE HOUSE SPARROW- CHIMNEY SWIFT- MOURNING DOVE FLICKER KINGBIRD CROW REDWINGED BLACKBIRD. CRACKLE COWBI RD SONG SPARROW BARE PASTURE HAY, SMALL MARSH SHRUB, FOREST URBAN FIELD GRASSLAND CLOVER GRAIN ORCHARD RESIDENTIAL Fig. 31.—Habitat preferences of common species of Illinois birds in summer as indicated by the population density of each species in each habitat. Each black bar represents the relative density of a given species in a given habitat; the sum of the relative densities for each species is 100 per cent. Data are from all zones of the state and from all summer censuses. 514 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 SPECIES SPARROW HAWK MOURNING DOVE LAPLAND LONGSPUR HORNED LARK BARE PASTURE, p., , _y, HAY, SMALL GRAIN SHRUB, p^ppey FIELD GRASSLAND '^'^^^°^ CLOVER STUBBLE ^"^^^ ORCHARD ^^^^^^ SWAMP SPARROW REDWINGED BLACKBIRD- EASTERN BLUEBIRD MOCKINGBIRD GOLDFINCH FLICKER SONG SPARROW DOWNY WOODPECKER MEADOWLARKS PURPLE FINCH WHITE -CROWNED SPARROW— WHITE-BREASTED NUTHATCH+- FIELD SPARROW » CHICKADEES » BOBWHITE » HOUSE SPARROW STARLING 1- JUNCO 25 |ipi 50 10 PER CENT SCALE RED-H WOODPECKER TURKEY VULTURE TUFTED TITMOUSE HAIRY WOODPECKER RED-BELLIED WOODPECKER- BLUE JAY ROBIN WHITE-THROATED SPARROW CARDINAL TREE SPARROW BARE PASTURE, pa,, ova; HAY, SMALL GRAIN yy^p a j SHRUB, pnRFc;T FIELD GRASSLAND ^^^^°^ CLOVER STUBBLE ^"^^^ ORCHARD ^°^^ST Fig. 32.—Habitat preferences of common species of Illinois birds in winter as indicated by the population density of each species in each habitat. Each black bar represents the relative density of a given species in a given habitat; the sum of the relative densities for each species is 100 per cent. Data are from all zones of the state and from all winter censuses. To the multiplicity of factors involved in this extremely complicated subject, man has, in recent years, added to the com- plexity. In a sense, we have entered into a new era characterized by the wide- spread, regular application to the land of potent chemicals—insecticides, herbicides, and fertilizers. The acreage of Illinois cornland treated with chemicals for con- trol of subterranean insects expanded from about 780,000 in 1958 (the last year of the second census period) to more than 3,500,000 acres in 1962 (Anon. 1963« : 1 ) . As we consider the increasing acreage of corn, soybeans, and other crops that are being treated with insecticides and herbi- cides, and the increasing acreage of road- side and other vegetation that is being killed with herbicides, we ask ourselves if we are not rapidly approaching the time when most of Illinois will be treated with toxicants of one sort or another. We are only beginning to understand some of the effects of these chemicals on birds. Among the most important research needs in the state are detailed, carefully planned, and controlled studies of the ef- fects of pesticides (insecticides and herbi- cides) on birds, their diets, their repro- duction, their survival. We have suggested that, with the increased use of insecticides in orchards, population densities of cer- tain species were reduced in this habitat. Mortality of birds as a result of applica- tions of pesticides in a wide variety of habitats and geographic areas has been described and discussed by many authors (including DeWitt & George 1959 ; Scott, Willis, & Ellis 1959; Anon. 1962). There is ample evidence that this mortality re- sults from both direct and indirect (through the food chain) intoxication (Bernard 1963:170, 188-90). Nesting success in a pesticide-treated area may be October, 1963 Graber & Graber: Bird Populations in Illinois 515 greatly reduced because of loss of natural insect foods, or the intoxication of ju- venile birds or adults (Hanson 1952:305- 8; DeWitt & George 1960:8-9; and others). We are still short of data on the cumulative effects of sublethal doses of pesticides on individual birds and the long- term effects on whole populations. Par- ticularly pertinent here is the evidence that certain widely used chlorinated hy- drocarbons reduce reproductive capabilitv in birds (DeWitt 1955:67b; 1956:865-6; Anon. 1962:45-7). What effect the widespread use of in- secticides and herbicides in the various habitats will have on the future popula- tions of Illinois birds remains to be seen. Because cultivated lands and urban resi- dential areas are the habitats that are being most widely and regularly treated with pesticides, the very species of birds that have been increasing their popula- tions in recent years may, in coming gen- erations, be the species that decline. Man and the Avifauna Whatever the genetic or ecological char- acteristics of the species involved, it is abundantly clear that man, among the various forces that shape our fauna, is the dominant force of change. In his use of the land for food production, com- mercial enterprises, home building, and other purposes, he selects (albeit unwit- tingly) for some species of birds and per- haps inevitably against others. In the histor\ of a fauna, 50 years is an extremely brief period, and the coming years will probably accentuate the loss in avifaunal variety, even though the number of birds increases. The most unfortunate aspect of man's domination of the land is not that he changes the environment but that he changes it so widely so quickly. Species evolution requires time. Natural cataclysms may alter habitats quickly but not widely, or widely but not quickly. It is man who combines the two. who changes the face of the earth not in mil- lennia but in decades. For the most part, man has utilized the land without regard for the natural fauna. In North America, conscious management of bird populations, except those of a few game species, has been negligible. Yet for the past several decades man has been un- wittingly manipulating bird populations on a wholesale scale. His domination has reached a critical and fearful level. Some obligation must go with this domination. Man has reached the stage when he must consider, in his manipulation of the en- vironment, more than just his own pri- mary needs. If there is to be a varied and interesting fauna for future generations to know, then management of the land must extend beyond human needs to the basic requirements of the fauna. Our lack of knowledge is the overriding deterrent to this type of management, but not the only one, and education of the public will have to follow the much-needed research. LITERATU RECITED Allen, J. A. ISSd. Ka>t\varii range of the western meadowlark. Nuttall Ornith. Club Bui. 5:53-4. American Ornithologists' Union 1957. Check-list of North American birds. 5th ed. American Ornithologists' Union. 691 pp. Anonymous 1900- Christmas birtl count. (A series of reports on annual Christmas bird counts, as pro- 1960. posed in Bird-Lore 2(6): 192. Reports published in Bird-Lore, Audubon Magazine, Audubon Field Notes, various issues and pages.) 1832. Abstract of the returns of the Fifth Census. 22nd Congress, 1st Session, House of Representatives Document 269. 51 pp. Duff Green, Washington, D. C. [1936.] Illinois crop and livestock statistics. 111. Dept. Ag. Circ. 438. 341 pp. 1962. Effects of pesticides on fish and wildlife: a review of investigations during 1960. V. S. Fish and Wildlife Service Circ. 143. 52 pp. 1963. Subterranean insects. The Illinois Natural History Survey Reports, February, 1963. 4 pp. Baker, Mrs. H. A, 1955- Two hay fields and grazed creek pasture. [Series of articles appearing under this 1961. and similar titles in annual breeding-bird census reports.] Audubon Field Notes, 1955, 9(6):423-4; 1956, 10(6):427-8; 1957, 11(6) :447; 1958, 12(6): 450; 1959, 13(6): 467-8; 1960, 14(6):498-9; 1961, 15(6) :511. Barnes. R. M. 1912. Breeding birds of Marshall Co., 111. Oologist 29:325-8. Barrows, Walter B. 1889. The English sparrow {Passer domcslicus) in North America, especially in its rela- tions to agriculture. U. S. Biol. Surv. Bui. 1. (Published as U.S. Dept. Ag. Div. Econ. Ornith. and Mammal. Bui. 1.) 405 pp. Bernard, Richard F. 1963. Studies on the effects of DDT on birds. Mich. State Univ. Mus. Biol. Ser. 2(3) : 155- 92. [Chapman, Frank M.] 1900. A Christmas bird-census. Bird-Lore 2(6):192. Conover, John H. 1953. Climatic changes as interpreted from meteorological data. Chap. 18, pp. 221-30, in Climatic change: evidence, causes, and effects; Harlow Shapley, ed. Harvard Uni- versitv Press, Cambridge. 318 pp. Cooke, Wells W. 1915. Preliminary census of birds of the United States. U. S. Dept. Ag. Bui. 187. 11 pp. 1916. Second annual report of bird counts in the United States, with discussion of results. U. S. Dept. Ag. Bui. 396. 20 pp. DeWitt, James B. 1955. Effects of chlorinated hvdrocarbon insecticides upon quail and pheasants. Ag. and Food Chem. 3(8) : 672-6". 1956. Chronic toxicitv to quail and pheasants of some chlorinated insecticides. Ag. and Food Chem. 4(10): 863-6. DeWitt, James B., and John L. George 1960. Bureau of Sport Fisheries and Wildlife pesticide-wildlife review: 1959. U. S. Fish and Wildlife Serv. Circ. 84. (Special scientific report: wildlife.) 36 pp. Eifrig, C. W. G. 1927. Notes from the Chicago area. Auk 44(3):431-2. Ewing, J. A., in charge 1959. Illinois agricultural statistics, annual summary 1959. Illinois Co-operative Crop Reporting Service. Springfield. 74 pp. Forbes, Stephen A. 1907. An ornithological cross-section of Illinois in autumn. 111. Lab. Nat. Hist. Bui. 7(9): 305-35. 1908. The mid-summer bird life of Illinois: a statistical study. Am. Nat. 42:505-19. 1913. The midsummer bird life of Illinois: a statistical study. 111. Lab. Nat. Hist. Bui. 9(6) :373-85. Forbes, Stephen A., and Alfred O. Gross 1921. The orchard birds of an Illinois summer. 111. Nat. Hist. Surv. Bui. 14(1): 1-8 + pis. I-VI. 1922. The numbers and local distribution in summer of Illinois land birds of the open country. 111. Nat. Hist. Surv. Bui. 14(6): 187-218 + pis. XXXV-LXX. 1923. On the numbers and local distribution of Illinois land birds of the open countrv in winter, spring, and fall. 111. Nat. Hist. Surv. Bui. 14( 10) :397-453. Graber, Richard R., and Jack S. Golden 1960. Hawks and owls: population trends from Illinois Christmas counts. 111. Nat. Hist. Surv. Biol. Notes 41. 24 pp. [516] October, 1963 Graber & Graber: Bird Populations in Illinois 517 Hagan, William T. 1958. The Sac and Fox Indians. University of Oklahoma Press, Norman. 287 pp. Hancock, Joseph L. 1888. Impeded migration and destruction of birds at Chicago. Auk 5(4): 432-4. Hanson, Harold C, and Charles W. Kossack 1957. Weight and body-fat relationship of mourning doves. Jour. Wildlife Mgt. 21(2): 169-81. 1963. The mourning dove in Illinois. 111. Dept. Cons. Tech. Bui. 2. 133 pp. Hanson, William R. 1952. Effects of some herbicides and insecticides on biota of North Dakota marshes. Jour. Wildlife Mgt. 16(3) : 299-308. Hickey, Joseph J., Editor 1937. Bird-Lore's first breeding-bird census. Bird Lore 39( 5) : 373-86. Hicks, Lawrence E. 1935. Small birds are not decreasing! Bird-Lore 37(5): 303-9. James, Douglas 1962. Winter 1961-62: dominated by movements of boreal birds and marked by still low numbers of eastern bluebirds. Audubon Field Notes 16(3) : 306-11. Kendeigh, S. Charles 1944. Measurement of bird populations. Ecol. Monog. 14( 1) :67-106. 1954. Oak-maple forest and forest edge {in Eighteenth breeding-bird census). Audubon Field Notes 8(6) :370-l. 1960. Oak-maple forest and edge (iw Twenty-fourth breeding-bird census). Audubon Field Notes 14(6): 502. Kendeigh, S. Charles, and Richard D. Brewer 1956. Oak-maple forest and forest-edge {in Twentieth breeding-bird census). Audubon Field Notes 10(6) : 434. Kendeigh, S. Charles, Marshall B. Eyster, and Robert K. Stubbs 1950. Oak-maple forest and forest-edge {in Fourteenth breeding-bird census). Audubon Field Notes 4(6) : 300. Kendeigh, S. Charles, and Nancy Joen Forsyth 1959. Oak-maple forest and edge {iti Twenty-third breeding-bird census). Audubon Field Notes 13(6) : 472-3. Kendeigh, S. Charles, and Walter Gillespie 1955. Oak-maple forest and forest-edge {in Nineteenth breeding-bird census). Audubon Field Notes 9(6):431. Kendeigh, S. Charles, Douglas James, and Charles Weise 1952. Oak-maple forest and forest-edge {in Sixteenth breeding-bird census). Audubon Field Notes 6(6) :310-1. 1953. Oak-maple forest and forest edge {in Seventeenth breeding-bird census). Audubon Field Notes 7(6) :347. Kendeigh, S. Charles, Robert V. Kennedy, George W. Cox, George C. West, and Walter L. Gillespie 1957. Oak-maple forest and forest edge {in Twenty-first breeding-bird census). Audubon Field Notes 11 (6): 452-3. Kendeigh, S. Charles, and Robert K. Stubbs 1951. Oak-maple forest and forest-edge {in Fifteenth breeding-bird census). Audubon Field Notes 5(6) :324. Kendeigh, S. Charles, and George C. West 1958. Oak-maple forest and edge {in Twenty-second breeding-bird census). Audubon Field Notes 12(6) :455. King, D. B., and R. K. Winters 1952. Forest resources and industries of Illinois. 111. Ag. Exp. Sta. Bui. 562. 95 pp. Livesay, Ann 1951. The past speaks to you. 111. State Mus. Story of 111. Ser. 7. 32 pp. Musselman, T. E. 1941. Bluebird mortality in 1940. Auk 58(3) : 409-10. Rand, A. L. 1956. Changes in English sparrow population densities. Wilson Bui. 68(1): 69-70. Ridgway, Robert 1915. Bird-life in southern Illinois. IV. Changes which have taken place in half a century. Bird-Lore 17(3) :191-8. Ross, R. C, and H. C. M. Case 1956. Types of farming in Illinois: an analvsis of differences by areas. 111. Ag. Exp. Sta. Bui. 601. 88 pp. Scott, Thomas G. 1958. The ornithologist's responsibility to the future. Wilson Bui. 70(4): 385-93. Scott, Thomas G., Yuell L. Willis, and Jack A. Ellis 1959. Some effects of a field application of dieldrin on wildlife. Jour. Wildlife Mgt. 23(4): 409-27. 518 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 Shaw. Samuel P.. and C. Gordon Fredine 1956. Wetlands of the I'nited States: their extent and their value to waterfowl and other wildlife, r. S. Fish and Wildlife Serv. Circ. 39. 67 pp. Smith. Harrv R.. and Paul W. Parmalee 1955. A distributional check list of the birds of Illinois. 111. State Mus. Pop. Sci. Ser. 4. 62 pp. Stone. George J. 1950. Breeding-bird census. Audubon Field Notes 4(2) :185-6. Temple. Wayne C. 1958. Indian villages of the Illinois country. Historic tribes. HI. State Mus. Sci. Papers 2(2). 218 pp. U. S. Bureau of the Census 1913. Thirteenth census of the United States taken in the year 1910. Vol. V, Agriculture, 1909 and 1910. 977 pp. U. S. Government Printing Office, Washington, D. C. 1961. U. S. Census of Agriculture: 1959. Vol. I, Counties. Part 12, Illinois. 255 pp. U. S. Government Printing Office, Washington, D. C. Wetmore, Alexander 1940. A check-list of the fossil birds of North America. Smithsn. Inst. Misc. Collect. 99(4). 81 pp. "^'eatter. Ralph E. 1943. The prairie chicken in Illinois. III. Nat. Hist. Surv. Bui. 22(4) :377-416. INDEX In this index, page numbers referring to figures and tables are in italic type ; page num- bers for principal references are in boldface type. Of necessity, variation occurs in some of the terms indexed. For example, cornfield in the index may sometimes refer to corn in the text; slate-colored junco in the index may refer to junco in the text. Shrubs in one place may be synonymous with slirub-groivn area in another. For certain sections dealing with bird species and with habitats, inclusive pages for each are given in boldface type ; for example, Robin, 485-6, Pasture, 408—12. Within the inclusive pages for any of these items, no text references to subdivisions of the items are indexed ; for example, the acreage of pasture and the bird populations in pasture as given in the text on page 409 are not indexed; however, the acreages of pasture shown in the graph on page 388 and mentioned on pages 440 and 457 are indexed under Pasture, as are the bird populations in pasture mentioned on pages 440, 441, and 457; dickcissel as mentioned on page 409 is indexed under the entry Dickcissel as a species in pasture. Common and scientific names of birds encountered in this study are listed in table 55, pages 459-62; the index includes references to the common but not the scientific names on these pages. Acreage censused {see also under each habi- tat), 396, 443 Acreage data, sources of, 387—8 Airfields (airports), 442, 458 Alfalfa, 386, 414, 416, 418, 420, 421-2, 438, 43S, 439, 439, 468, 469, 472, 477, 478, 479, 484, 486, 487, 488, 489, 490, 491, 492, 493, 495, 496, 497, 500, 510 acreage censused, 396, 423 acreage in state, 3SS, 441 avifauna of, 423 common species in, 424 statistical data on populations in, 423 Annotated list of common bird species, 463—500 Avifauna, specific changes in, 503—4 B Bare-field or bare-ground habitat, 397, 401, 438, 439, 497, 509, 513, 514 Barley, 440, 448 acreage censused, 396 Beans (see also Soybeans), 408, 471, 478, 482 Bird populations {sec also individual species) annotated list of common species, 463—500 avifaunal differences between censuses, 463 of common species, 1909 and 1957, 507 comparison of data for summer habitats, 437-40 comparison of data for winter habitats, 453— 6 density in three zones, 442-3, 457-8, 458 loss between 1909 and 1957, 505 number of birds eliminated bj' forest remov- al, 502 number of birds in summer habitats, 438—9 number of birds in winter habitats, 456 number of common species, 508 number of species in summer habitats, 439— 40 number of species in winter habitats, 456 previous to 1800, 501-2 statewide, 513 statewide summer, 440—3, 503 statewide winter, 456-8, 508 in summer habitats, 396—J43 variations in statewide, 442 variations in summer and winter, 392—3 in winter habitats, 443—58 Bird species account of, 458—500 encountered in strip censuses, 459-62 number of identified, 458 Bittern, American, 459, 463 as species in marsh, 425 Bittern, least, 459, 463 as species in marsh, 425 Blackbird spp., 509 Blackbird, Brewer's, 461, 463 range extension, 509 as species in corn, 398; hay, 417; pasture 411 Blackbird, redwinged, 461, 462, 490, 490-1 495, 508, 510, 513 habitat preferences, 513, 514 population (statewide), 504 population for all habitats in study, 507 as species in alfalfa, 422, 423, 424; clover 420, 421, 422, 424; corn, 397, 398, 400, 400 446; fallow fields, 414, 415; forest, 432 455; grassland, 412, 413; hay, 389-90 390, 416, 417, 418, 419, 424; marsh, 424 425; oats, 404, 405, 407; orchard, 429, 430 430; pasture, 409, 410, 412, 412, 450; plowed fields, 403; shrubs, 424, 425, 426 427, 428, 454; soybeans, 401, 402, 447 \ wheat, 406, 407, 408 ; woodland, 434 Blackbird, rusty, 461, 463 as species in corn, 446 Blackbird, yellow-headed, 461, 463 range extension, 509 as species in fallow fields, 415; marsh, 425 "Blackbirds," 491 Bluebird, eastern, 393, 461, 462, 485, 486 habitat preferences, 513, 514 as species in clover, 421 ; corn, 398, 400, 445, 446; fallow fields, 415, 451; forest, 432 455; hay, 418, 453; marsh, 425; oats, 405 pasture, 410, 450; plowed fields, 403 shrubs, 427, 454; small grain, 448; wheat, 449; woodland, 392, 434 Bluegrass, 409, 430, 451 Bobolink, 461. 489 habitat preferences, 513 range extension, 509 population for all habitats in study, 507 as species in alfalfa, 423, 424; clover, 420, 421, 422, 424; corn, 398; grassland, 413; r5i9] 520 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 hav, 389, 390, 417, 418, 419, 424; marsh, 424, 425^; oats, 404, 405, 407; pasture, 410; shrubs, 427 Boliwhite. 459, 462, 466-7 habitat preferences, 51S, 514 population for all habitats in study, 507 as species in alfalfa, 423; corn, 39S, 445, 446, 446; clover. 420, 421, 422; fallow fields, 415. 451. 452; forest, 432, 453, 455; grass- land. 413; hav. 417, 419. 452, 453; oats, 405; orchard. 429. 430; pasture, 410, 450; plowed fields, 403; shrubs, 426. 427, 453, 454; snnall grain, 44S ; soybeans, 402; wheat, 407 Breeding species, definition of, 389 Bromegrass, 416, 420 Bunting, indigo, 462. 463. 494-5, 512 habitat preferences, 513 population for ail habitats in study, 507 as species in alfalfa, 423 ; clover, 421 ; corn, 39S, fallow fields, 415; Jorest, 432, 435; grassland, 413; hay, 417; oats, 405; or- chard, 429, 430, 430; pasture, 410; plowed fields, 403; shrubs, 424, 425, 426, 427, 428; sovbeans, 402; wheat, 406, 407; woodland, 434 Bunting, snow, 462, 463 as species in small grain, 448 Cacti, frontispiece Caprimulgiis spp. in forest, 433 Cardinal. 453, 462, 462, 493-4 habitat preferences, 513 , 514 range extension, 501, 509 as species in alfalfa, 423 ; corn, 398, 445, 446; fallow fields, 415, 451, 452; forest, 432, 435, 436, 453, 455; hay, 418; oats, 405; orchard, 429, 430, 430; pasture, 410, 450. 452; shrubs, 424, 426, 427, 428, 453, 454; urban residential areas, 436; wheat, 407, 449; woodland, 392, 434 Catbird, 460, 463, 483-4, 484, 508 habitat preferences, 513 as species in corn, 398; forest, 432; hay, 418; marsh. 425; oats, 405; orchard, 429, 430; pasture, 410; shrubs, 424, 426, 428; urban residential areas, 436, 437, 437; wheat, 407; woodland, 434 Cattails, 424, 504 Cemeteries, 442, 458 Census, breeding-bird, in hayfields, 389-91 Census, strip area, size of adequate, 386-7 counties included in, 385, 386 data on areas of different sizes, 387 dates of, 385-6 description of method, 383—9 evaluation of method, 389—93 zones, boundaries between, 386 zones, how defined, 388 Chat, yellow-breasted, 461 habitat preferences, 513 as species in fallow fields, 415; forest, 432; orchard, 429; pasture, 411; shrubs, 424, 426, 427, 428; woodland, 434 Chickadee spp., 388, 460, 481-2, 482, 483 habitat preferences, 513, 514 as species in corn. 445, 446, 446; fallow fields, 451; forest, 432, 435, 453. 455; hay, 453; pasture, 411, 450; plowed fields, 447; shrubs, 426, 428, 454; woodland, 392. 434 Chickadee, black-capped. 388. 460, 481-2, 482 Chickadee, Carolina, 388, 460, 481-2, 482 range extension, 509 as species in orchard, 429, 430; shrubs, 427 Chicken, greater prairie, 459, 463, 466 as species in clover. 420, 421 ; corn, 398; hay, 418; pasture, 411; wheat, 407 Chlorinated hvdrocarbons. 515 Clover (clove'r fields). 418-21, 422, 468, 469, 472, 473, 513, 514 acreage in state, 388 Clover, Ladino, 420 Clover, red, 389, 414, 416, 418-20, 421, 422, 430, 438, 438, 439, 439, 466. 468. 469, 470. 472, 475, 476, 477, 479, 480, 484. 485, 486, 487, 488, 489, 490, 491, 492, 493, 495, 496, 497, 499 acreage censused, 396, 420, 421 avifauna of, 421 common species in, 422, 424 statistical data on populations in, 420 Clover, sweet, 389, 414-6, 418, 420-1, 438, 438, 439, 469, 472, 477, 478, 479, 480, 484, 489, 490, 491, 492, 493, 495, 496, 499 acreage censused, 396, 422 avifauna of, 422 Common names of birds, list of, 459-62 Common species of birds breeding populations of, 1909 and 1957, 507 definition of, 387 habitat preferences, 513, 514 Control of problem bird species, 511 Coot, American, 459, 463 as species in marsh, 425 Cornfield (corn), frontispiece, 383. 386, 396, 397-401, 399, 401, 405, 406, 408, 438, 438, 439, 439, 440, 443, 443-7, 444, 447, 448, 450, 452, 456, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 490, 491, 492, 493, 495, 496, 497, 498, 500, 502, 514 acreage censused, 396, 397, 398-9, 443, 446 acreage in state, 388, ^W,' 445, 456 avifauna of, 398-9, 445, 446 bird populations in, 392, 392, 442 common species in, 397, 400, 400, 414 statistical data on populations in, 397 Cowbird, brown-headed, 461, 462, 492-3 habitat preferences, 513, 514 population for all habitats in study, 507 as species in alfalfa, 423; clover, 420, 421, 422; corn, 398; fallow fields, 415; forest, 432; hay, 417, 424; grassland, 413; marsh, 425; oats, 404, 405; orchard, 429; pasture, 409, 410; plowed fields, 403; shrubs, 424, 426, 427, 428, 454; small grain, 448; soy- beans, 402; urban residential areas, 436; wheat, 407, 449; woodland, 434 Creeper, brown, 460 as species in forest, 455; woodland, 392 Crow, common, 460, 462, 480—1 habitat preferences, 513, 514 population for all habitats in study, 507 as species in alfalfa, 423; clover, 421, 422; corn, 398, 400, 445, 446, 446; fallow fields, October, 1963 Graber & Graber: Bird Populations in Illinois 521 415, 451 \ forest, 432, 435, 453, 455; grass- land, 413 \ hay, 417, 419, 453 \ marsh, 425; oats, 405; orchard, 429; pasture, 410, 450, 452; plowed fields, 403; shrubs, 426, 454; small grain, 44S, 449; soybeans, 447; wheat, 407, 449; woodland, 392, 434 Cuckoo spp., 472 Cuckoo, black-billed, 459, 472 as species in forest, 433 ; pasture, 411 ; plowed fields, 403 Cuckoo, yellow-billed, 459, 463, 472, 505 habitat preferences, 513 as species in corn, 399; fallow fields, 415; forest, 432; hay, 418; marsh, 425; orchard, 429; pasture, 410; shrubs, 426, 427 ; wheat, 407 D Dendrocopos spp. in forest, 433, 455; wood- land, 392, 434 Dickcissel, 462, 463, 495, 510 habitat preferences, 513 population for all habitats in study, 507 as species in alfalfa, 422, 423; clover, 420, 421, 422, 424; corn, 398; fallow fields, 414, 415; grassland, 413; hay, 389, 390, 416, 417, 418, 419; oats, 405; orchard, 429, 430; pasture, 409, 410; plowed fields, 403; shrubs, 426, 42S; soybeans, 402; wheat, 406, 407, 408 Discussion, 500—15 Dove, mourning, 453, 459, 462, 469-72, 505, 508, 512 habitat preferences, 513, 514 population for all habitats in study, 507 as species in alfalfa, 423, 424; clover, 421, 422; corn, 392, 397, 398, 400, 445, 446, 446; fallow fields, 414, 415, 451; forest, 432, 435, 455; grassland, 413; hay, 417, 419, 424, 453; marsh, 425; oats, 404, 405; orchard, 429, 430, 430; pasture, 410; plowed fields, 403; shrubs, 424, 426, 427, 428, 454; small grain, 448; soybeans, 401, 402, 447; urban residential areas, 436, 437; wheat, 406, 407, 408, 449; woodland, 434 Dove, rock, 459, 463, 511 as species in commercial urban areas, 441 ; urban residential areas, 436, 437, 437 Drainage ditches, 479, 487, 490, 491, 492, 494, 495, 499 Duck, black, 459, 463 Duck, wood, 459, 463 Eagle, bald, 459, 463 Eagle, golden, 459, 463 as species in forest, 455 Edge (edge shrub, road edge; see also Shrub habitat and Shrub-grown area), 400, 412, 426, 428, 438, 445, 446, 452, 456, 464, 466, 467, 469, 471, 472, 473, 476, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 490, 491, 492, 493, 494, 495, 497, 498, 499, 502, 505, 506, 510, 511, 512 acreage in state, 442, 510 bird populations in, 442 Egret, common, 459, 463 as species in forest, 433 ; grasssland, 413 Elm diseases, 511 Evolution, 501, 502, 503, 515 Fallow fields, 412, 413-4, 424, 438, 438, 439, 439, 443, 444, 452, 456, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 479, 480, 482, 483, 484, 486, 487, 488, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 514 acreage censused, 396, 414, 415, 440, 443, 451 acreage in state, 388, 457 avifauna of, 415, 451 bird populations in, 440, 457 common species in, 414 statistical data on populations in, 414 Farm and crop acreage, various years, 502 Fencerow, 425, 510 Fertilizers, 514 Finch, purple, 462 habitat preferences, 514 as species in forest, 455; pasture, 450; shrubs, 454 Flicker, yellow-shafted, 460, 462, 473-4, 474, 475, 505, 511, 512 habitat preferences, 513, 514 population (statewide), 503 population for all habitats in study, 507 as species in alfalfa, 423 ; clover, 421 ; corn, 398, 400, 445, 446; fallow fields, 415, 451; forest, 432, 436, 453, 455; grassland, 413; hay, 417, 419, 453; oats, 405; orchard, 429, 430, 430; pasture, 410, 450; plowed fields, 403, 447; shrubs, 427, 454; small grain, 448; urban residential areas, 436; wood- land, 392, 434 Flycatcher spp., 476, 477 Flycatcher, Acadian, 460, 476 range extension, 509 as species in forest, 432; orchard, 429; woodland, 434 Flvcatcher, great crested, 460, 463, 476, 511 habitat preferences, 513 as species in fallow fields, 415; forest, 432, 435, 436; hay, 418; orchard, 429, 430; pasture, 411; shrubs, 426, 427; urban resi- dential areas, 436; woodland, 434 Flycatcher, least, 460, 463 Flycatcher, Traill's, 460, 476, 510 as species in corn, 398; hay, 41S; marsh, 425 ; shrubs, 426 Flycatcher, yellow-bellied, 460, 463 Forbes-Gross method of censusing; see Census, strip Forbs, 412 Forest (see also Woodland), frontispiece, 383, 389, 393, 424, 430-6, 435. 437, 438, 438, 439, 439, 440, 443, 444, 445, 446, 453, 456, 457, 463, 464, 465, 466, 469, 470, 471, 472, 473, 474, 475, 476, 477, 479, 480, 481, 482, 483, 484, 485, 486, 488, 489, 490, 491, 492, 493^ 494_ 495^ 499, 501, 502, 507, 509, 510, 511, 513, 514 acreage censused, 396, 431, 432-3, 443, 455 acreage in state, 388, 441, 457, 501, 502 avifauna of, 432-3, 455 bird populations in, 441, 457, 501-2 statistical data on populations in, 431 522 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 Gallinule, common, t/59. 463 Garden crops (vegetables; see also Vegetable crops), 440 acreage censused, 396 acreage in state, 440, 456 bird populations in, 456 Gnatcatcher, blue-gray, 461, 463 as species in forest, )-32, 435; shrubs, 42i ; woodland, 4-34- Goldfinch. American, 462, 462, 495-6 habitat preferences, S13, 514 as species in alfalfa, 423 \ clover, 421, 422 \ corn. 39S, 445, 446; fallow fields, 415, 451 ; forest, 432, 453, 455; grassland, 413; hay, 417, 453; marsh, 425; oats, 405 ; orchard, 429, 430; pasture, 410, 412, 450, 452; shrubs, 424, 426, 427, 428, 454; soybeans, 401, 402, 447; wheat, 449; woodland, 434 Goose, blue, 459, 463 Goose, Canada, 459, 463 as species in forest, 389, 455; soybeans, 447; wheat, 449 Grackle, common, 461, 462, 492, 509, 511 habitat preferences, 513 population for all habitats in study, 507 as species in alfalfa, 423; clover, 420, 421, 422; corn, 397, 39S, 400; fallow fields, 414, 415; forest, 432; grassland, 413; hay, 417, 419, 424 ; marsh, 424, 425 ; oats, 404, 405 ; orchard, 429, 430; pasture, 409, 410, 450; plowed fields, 403; shrubs, 424, 426, 428; soybeans. 401, 402; urban residential areas, 436, 437, 437; wheat, 406, 407; woodland, 434 Grain crops [see also Small grain), 404 Grasslands, ungrazed (grasslands), frontis- piece, 412, 413, 414, 416, 418, 424, 438, 438, 439, 439, 440, 441, 449, 452, 464, 465, 466, 469, 470, 471, 473, 474, 475, 477, 478, 479, 480, 485, 486, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 501, 502, 504, 506, 507, 508, 509, 513, 514 acreage censused, 396, 413 acreage in state, 388, 440 avifauna of, 413 bird populations in, 440 Grebe, horned, 459, 463 as species in marsh, 425 Grosbeak, blue, 462, 463 as species in forest, 433; shrubs, 427 Grosbeak, rose-breasted, 462 as species in corn, 399; forest, 433 Gull, herring, 459, 463 Gull, ring-billed. 459, 463 H Habitat preferences of common species, 513, 514 Habitat, summer bird populations in, 396—443 comparison of bird populations in, 437—40, 438, 439 statewide bird population estimate, 440—3 Habitat, winter bird populations in, 443—58 comparison of bird populations in, 453—6 statewide bird population estimate, 456—8 Habitats and future of the avifauna, 509—15 in order of avifaunal variety, 509 in order of population densities, 509 Hawk spp. as species in corn, 445; fallow fields, 415; forests, 433, 455; hay, 453; pasture, 411, 450; plowed fields, 447; small grain, 448 Hawk, broad-winged, 459 Hawk, Cooper's, 459, 463 as species in forest, 433 Hawk, marsh, 459 as species in corn, 446; pasture, 411, 450; shrubs, 454; wheat, 449 Hawk, red-shouldered, 459 as species in corn, 399; forest, 433, 455; hay, 418; pasture, 450; plowed fields, 403 Hawk, red-tailed, 459, 463, 464-5 as species in corn, 399, 446 ; fallow fields, 451; forest, 432, 455; pasture, 411, 450; plowed fields, 403; shrubs, 426; small grain, 448; soybeans, 447; woodland, 434 Hawk, rough-legged, 459 as species in corn, 445; hay, 453; wheat, 449 Hawk, sparrow, 459, 462, 464, 465-6 habitat preferences, 514 as species in corn, 398, 445, 446; fallow- fields, 415, 451 ; forest, 432, 455 ; hay, 417, 453; oats, 405; pasture, 410, 450; shrubs, 427, 454; small grain, 448; wheat, 407, 449 Hay (hayfields), mixed (see also Hayfields), 414-8, 420, 422, 438, 438, 439, 439, 440, 441, 452, 465, 466, 468, 469, 471, 472, 473, 475, 476, 477, 479, 480, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 495, 496, 497, 499, 502, 504, 507, 508, 509, 510, 513, 514 acreage censused, 396, 416, 417-8, 443, 453 acreage in state, 388, 441, 457 avifauna of, 417-8, 453 bird populations in, 441, 457, 510 common species in, 419 , 424 statistical data on populations in, 416 Hayfields (hay; see also Hay, mixed), 383, 386, 389, 390, 391, 391, 393, 404, 418, 420, 422, 438, 439, 443, 444, 456, 466, 467, 468, 469, 470, 472, 473, 474, 476, 482, 484, 487, 489, 490, 491, 495, 497, 499, 504 Hedgerows (hedge), 428, 466, 467, 469, 471, 472, 473, 477, 479, 480, 483, 484, 485, 487, 491, 492, 493, 494, 495, 497, 498, 499, 505, 510 acreage censused, 396 acreage in state, 442 bird populations in, 442 Herbicides, 477, 485, 505, 514, 515 Heron, black-crowned night, 459 as species in corn, 399; marsh, 425; oats, 405; pasture, 411 Heron, great blue, 459 as species in corn, 399; forest, 433; marsh, 425 Heron, green, 459, 463 as species in forest, 433; hay, 418; marsh, 425; pasture, 411 Heron, little blue, 459, 463 Highways, 442 acreage in state, 512 October, 1963 Graber & Graber: Bird Populations in Illinois 523 Hummingbird, ruby-throated, 4^60 as species in clover, 421 \ forest, 4-32; hay, 417 \ shrubs, 426; woodland, 4i4 I Illinois, total land area, 440 Insecticides, 477, 479, 485, 504, 514, 515 Jay, blue, 460, 462, 479-80, 480, 481, 504, 505, 512 habitat preferences, 513, 514 population for all habitats in study, 507 as species in clover, 421 ; corn, 39S, 445; fal- low fields, 415, 451; forest, 432, 435, 436, 453, 455; grassland, 413; hay, 41S, 453; oats, 405; orchard, 429, 430; pasture, 410, 450; shrubs, 426, 427, 454; urban residen- tial areas, 436; woodland, 392, 434 Junco, slate-colored, 462, 463, 497-8, 498 habitat preferences, 514 as species in corn, 445, 446, 446 ; fallow fields, 451, 452; forest, 453, 455; hay, 453; pasture, 450, 452; plowed fields, 447; shrubs, 453, 454; small grain, 448; soy- beans, 447; wheat, 449; woodland, 392 K Killdeer, 459, 462, 467-8 habitat preferences, 513 as species in alfalfa, 423; clover, 421; corn, 39S, 400; fallow fields, 415; grassland, 413; hay, 417, 453; marsh, 425; oats, 405; pasture, 410; plowed fields, 401, 403; soy- beans, 402; wheat, 449 Kingbird, eastern, 460, 463, 476-7, 504, 505 habitat preferences, 513 as species in alfalfa, 423; clover, 421; corn, 398, 400; fallow fields, 415; forest, 433; hay, 417, 419 ; oats, 405 ; orchard, 429, 430 ; pasture, 410; plowed fields, 403; shrubs, 426, 428 Kingfisher, belted, 460 as species in corn, 399; forest, 432, 455; marsh, 425; pasture, 411 ; shrubs, 427 Kinglet, golden-crowned, 461 as species in forest, 455; woodland, 392 Kinglet, ruby-crowned, 461, 463 as species in shrubs, 454 Lark, horned, 439, 457, 460, 462, 477-8, 500, 502, 504, 509, 513 habitat preferences, 513, 514 population (statewide), 504 population for all habitats in study, 507 as species in alfalfa, 423, 424; clover, 421, 422; corn, 392, 397, 398, 400, 400, 445, 445, 446, 447; fallow fields, 415, 451, 452; grassland, 413; hay, 417, 452, 453; oats, 405; pasture, 410, 450, 452; plowed fields, 401, 403, 447, 448, 456 ; shrubs, 427 ; soy- beans, 401, 402, 447, 448 ; small grain, 448, 449; wheat, 407, 449, 450 Legumes, 414, 416, 477, 510 Longspur, Lapland, 457, 462, 500 habitat preferences, 514 as species in corn, 392, 445, 446, 446; hay, 452, 453; pasture, 450; plowed fields, 403, 447, 448, 456; soybeans, 447; small grain, 448, 449 ; wheat, 449, 450 Longspur, Smith's, 462, 463 M Mallard, 459, 463 as species in forest, 455; marsh, 425 Man and the avifauna, 515 Man as dominant force of change, 515 Managed habitats development of, 502—3 specialization in, 504—6 Marsh (marshland; see also Wetlands), 385, 422-4, 438, 438, 439, 443, 463, 468, 469, 480. 484, 486, 487, 489, 490, 491, 492, 493, 495, 496, 499, 501, 502, 504, 509, 510, 513 acreage censused, 396, 425, 443 acreage in state, 388, 441, 502, 510 avifauna of, 425 bird populations in, 441, 501-2, 510 Martin, purple, 460, 478, 503, 508 habitat preferences, 513 as species in corn, 398; fallow fields, 415; hay, 417; oats, 405; pasture, 410; soy- beans, 402; urban residential areas, 436, 437 ; wheat, 407 Meadowlark spp., 388, 389, 461, 462, 489-90, 508, 512 habitat preferences, 513, 514 population for all habitats in study, 507 as species in alfalfa, 423, 424; clover, 420, 421, 422, 424 ; corn, 398, 445, 446, 446 ; fal- low fields, 415, 451, 452; forest, 433, 455; grassland, 413; hay, 389, 390, 390, 416, 417, 418, 419, 424, 452, 453; marsh, 424, 425; oats, 405; pasture, 410, 411, 412, 450, 452; shrubs, 426, 428, 454; small grain, 448, 449, 450-1, 457; soybeans, 402, 447, 450 ; wheat, 407, 449, 450 Meadowlark, eastern, 388, 461, 489-90 as species in alfalfa, 422; clover, 420; fal- low fields, 414; grassland, 412; hay, 416, 419; oats, 407; orchard, 429, 430, 430; pasture, 409; plowed fields, 403; wheat, 408 Meadowlark, western, 388, 461, 463, 489-90 range extension, 509 as species in clover, 420; grassland, 412; hay, 418 Melospiza spp. in fallow fields, 451; hay, 41$; shrubs, 454 Mockingbird, 460, 483, 484, 505, 508 habitat preferences, 513, 514 range extension, 501, 509 as species in corn, 398, 400, 445; fallow fields, 415, 451; forest, 455; hay, 418; or- chard, 429, 430, 430; pasture, 410; plowed fields, 403; shrubs, 427, 454; soybeans, 402; urban residential areas, 436; wheat, 407, 449 N Nighthawk, common, 460, 512 as species in corn, 399; fallow fields, 415; hay, 417; orchard, 429; pasture, 411 Nuthatch, white-breasted, 460, 462 habitat preferences, 514 524 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 a> species in corn, 445; forest, 432, 453, 455 \ pasture, 411, 450 \ shrubs, 454; woodland, 392 O Oats (oat fields), 401-7. 438, 43S, 439, 448, 466, 469, 470, 473, 475, 477, 479, 480, 484, 485, 486, 488. 489, 490, 491, 492, 493, 495, 496. 497, 502. 509 acreage censused. 396, 404, 405 acreage in state, 3SS, 440 a\ifauiia of. 405 bin! populations in, 440, 442 common species in, 404 statistical data on populations in, 404 Open-field areas (habitat), 383, 386-7. 393, 400, 401, 414, 418, 424, 431, 433. 445, 446, 468, 469, 476, 477, 478, 479, 480, 487, 489, 494, 498, 510, 512 Orchard. 383. 385, 42S, 429-30. 438, 43S, 439. 439, 443, 466, 469, 470, 471, 472, 475, 476. 477, 479, 480, 481, 482, 483, 484, 485. 487, 488, 490, 491. 492. 493, 494, 495, 496, 497, 498, 499, 504. 506, 509, 512, 513, 514, 514 acreage censused, 396, 429, 443 acreage in state, 38S, 441, 502, 511 avifauna of, 429 bird populations in, 441, 511 common species in, 430 Oriole, Baltimore, 461, 463, 509 as species in clover, 421; corn, 399; forest, 433; oats, 405; orchard, 429; pasture, 410; shrubs, 426 Oriole, orchard. 461, 463, 491-2, 504, 505, 509 habitat preferences, 513 population (statewide), 512 as species in clover. 421; corn, 39S; fallow fields. 415; forest, 433; hay, 418; orchard, 429_, 430, 430; yasiure, 410; shrubs, 426, 427 ; wheat, 407 Ovenbird, 461, 463 as species in forest, 432, 436; woodland, 434 Owl, barred, 459 as species in forest, 433 Owl, great horned, 459, 463 as species in forest. 433, 455 Owl, long-eared. 459 as species in forest, 455; shrubs, 454 Owl, saw-whet, 460, 463 as species in shrubs, 454 Owl. short-eared, 460, 463 as species in corn, 446; fallow fields, 451; small grain, 448 Partridge, gray, 459, 463, 466 as species in clover, 421; shrubs, 426 Partis, 389 Pasture (pastureland), 393, 408-12, 408, 413, 418, 424, 438, 438, 439, 439, 441, 443, 444, 451-2, 452, 456, 464, 465, 466, 467, 468, 469, 470, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 483, 484, 485, 486, 487, 488. 489, 490, 491, 492, 493, 494, 495, 496. 497, 498. 499, 502. 504, 505, 510, 513, 514 acreage censused, 396, 409, 410-1, 443, 450 acreage in state, 388, 440, 457 avifauna of, 410-1, 450 bird populations in, 440. 441, 457 common species in. 412 populations of breeding species in, 412 statistical data on populations in, 409 Pesticides, 514, 515 Pewee, eastern wood, 460, 463, 476 as species in forest, 432, 435; pasture, 411; shrubs. 426; urban residential areas, 436; woodland, 434 Pheasant, ring-necked, 383, 459, 463, 466 as species in alfalfa, 423 ; clover, 420, 421 corn. 392, 398, 446; fallow fields, 415, 451 forest, 433; hay, 391. 417,453; marsh. 425 oats, 405; pasture. 411; small grain, 448 soybeans, 402; shrubs, 426 Phoebe, eastern, 460, 463, 476 as species in corn, 398; forest, 433; hay, 418; oats, 405; orchard, 429; pasture, 411; shrubs, 426 Pipit, Sprague's, 461, 463 as species in hay, 453 Pipit, water, 461, 463 Plover, upland {sec Upland plover) Plowed fields (plowed ground). 383, 401, 438, 439, 439, 440, 443, 444, 447, 448, 449, 452, 456, 468, 469, 470, 475, 477, 480, 482, 483, 486, 490, 495, 497, 500, 502, 509 acreage censused, 396, 403, 443, 447 acreage in state, 456 avifauna of, 403, 447 bird populations in, 456 common species in, 403 , 414 Poa pratensis, 409 Population changes and latitude, 508 Population density and avifaunal variety, 507-8 Population density in relation to size of census area, 391. 391 Prairie, frontispiece, 443, 468, 470, 495, 501-2, 504 Quail {see Bobwhite) Q R Rail spp. in marsh, 425 Rail, king, 459 as species in marsh, 425 Rail, Virginia, 459, 463 as species in marsh, 425 Railroad rights-of-way, 412 Railroad tracks. 442, 512 Range extension of certain species {see also individual species), 508—9 Redstart, American, 461 as species in forest, 432; grassland, 413; shrubs, 426, 428; woodland. 434 Roadside (roadside shrubs), 425, 442. 464, 467, 472, 477. 478. 479, 486, 488, 510, 514 acreage in state. 512 Robin, 460, 462. 485-6, 504, 505, 508, 511 habitat preferences, 513, 514 population for all habitats in study, 507 as species in alfalfa, 423; clover, 421, 422; corn, 398, 400, 445, 446; fallow fields, 415, 451; forest, 432, 453, 455; grassland, 413; hay, 417; marsh, 425; oats, 405; orchard, 429, 430, 430; pasture, 410, 450; plowed October, 1963 Graber & Graber: Bird Populations in Illinois 525 fields, 403 \ shrubs, 426, 427, 454\ soybeans, 402 \ urban residential areas, 436, 437, 431 \ wheat, 401, 449 \ woodland, 434 Row-crop habitat (row crops), 438, 439, 440, 449, 452, 456, 468, 474, 477, 497, 502, 507, 509, 512 acreage in state, 440, 456 bird populations in, 440, 456 Rye, 440, 448, 470 acreage censused, 396 Sandpiper, spotted, 4S9, 467 as species in corn, 398 \ marsh, 425 \ pasture, 411 ; soybeans, 402 Sapsucker, yellow-bellied, 460, 463, 473 as species in forest, 455 Savanna-like habitats, 408, 469, 473, 475, 476, 479, 503, 505, 505, 506, 506, 507, 508, 513 Scaup, lesser, 459, 463 Scientific names of birds, list of, 459-62 Sedges, 424 Shrike, loggerhead, 461, 462 as species in clover, 421; corn, 398, 445 \ fallow fields, 415, 451 \ hay, 418\ oats, 405; orchard, 429; pasture, 410; plowed fields, 403 ; shrubs, 454 ; small grain, 448 ; soybeans, 402 Shrike, northern, 461, 463 Shrub (shrubby) habitat {see also Shrub- grown area and Edge), 386, 413, 429, 438, 439, 444, 445, 446, 457, 464, 466, 469, 470, 471, 474, 476, 477, 479, 480, 481, 483, 484, 485, 486, 487, 489, 490, 491, 493, 495, 496, 497, 498, 499, 501, 502, 505, 509, 510, 511, 512, 513, 514 acreage censused, 396 acreage in state, 388 Shrub-grown area or habitat (see also Shrub habitat and Edge), 383, 424-8, 437, 438, 439, 443, 452-3, 456, 466, 469, 471, 472, 473, 474, 475, 476, 480, 482, 483, 484, 485, 486, 487, 491, 492, 493, 494, 495, 496, 497, 498, 499 acreage censused, 426-7 , 443 , 454 acreage in state, 441, 457 avifauna of, 426-1 , 454 bird populations in, 441, 457, 510 common species in, 421 , 428 Small grain, 386, 438, 439, 440, 443, 444, 448-9, 451, 456, 466, 467, 468, 469, 471, 472, 474, 477, 478, 481, 487, 490, 491, 493, 495, 496, 497, 500, 502, 504, 509, 510, 513, 514 acreage censused, 396, 443 , 448 acreage in state, 457 avifauna of, 448 bird populations in, 457 Snipe, common, 459, 463, 467 as species in marsh, 425 Sora, 459, 463 Soybean fields (sovbeans; see also Beans), frontispiece, 383, 401, 401, 438, 438, 439. 439, 440, 441, 443, 444, 447-8, 450, 456, 468, 469, 477, 479, 484, 488, 490, 491, 492, 495, 496, 497, 500, 514 acreage censused, 396, 402, 443 , 441 acreage in state, 388, 440, 456 avifauna of, 402, 441 bird populations in, 456 statistical data on populations in, 402 Sparrow spp. in small grain, 457 Sparrow, Bachman's 462, 510 as species in fallow fields, 415; hay, 411; oats, 405; pasture, 411 ; shrubs, 421 Sparrow, chipping, 462, 498, 505 as species in clover, 422; corn, 398; fallow fields, 415; oats, 405; orchard, 429; pas- ture, 410; urban residential areas, 436 Sparrow, field, 462, 462, 498-9, 505 habitat preferences, 513, 514 population for all habitats in study, 501 as species in alfalfa, 423 ; clover, 421 , 422 ; corn, 398; fallow fields, 414, 415, 451; forest, 432, 455; grassland, 413; hay, 411, 419; oats, 405; orchard, 429, 430, 430; pasture, 409, 410, 412, 412; plowed fields, 403; shrubs, 424, 425, 426, 421, 428, 454; soybeans, 402; wheat, 401; woodland, 434 Sparrow, fox, 462 as species in corn, 445; fallow fields, 451; forest, 455; pasture, 450; shrubs, 454 Sparrow, grasshopper, 462, 463, 496—7 habitat preferences, 513 as species in alfalfa, 423 ; clover, 420, 421, 422; corn, 399; fallow fields, 415; grass- land, 413; hay, 389, 390, 390, 416, 411, 419; oats, 405; orchard, 429; pasture, 410; shrubs, 421; soybeans, 402; wheat, 401, 408 Sparrow, Harris', 462, 463 as species in shrubs, 454 Sparrow, Henslow's, 462 as species in hay, 389, 390, 390, 411 Sparrow, house, 461, 462, 486, 488-9, 508, 511, 512 habitat preferences, 513, 514 population (statewide), 503 population for all habitats in study, 501 as species in alfalfa, 423; clover, 421, 422, 424; commercial urban areas, 441; corn, 397, 398, 445, 446; fallow fields, 415, 451j forest, 433, 455; grassland, 413; hav, 411, 419, 453; oats, 405, 407; orchard, 429, 430, 430; pasture, 409, 410, 412, 450; plowed fields, 403, 441; shrubs, 426, 453,_454; small grain, 448; soybeans, 402, 441; ur- ban residential areas, 436, 437, 431; wheat, 406, 401, 449 Sparrow, lark, 462, 497, 505, 512 as species in clover, 422; corn, 398; fallow fields, 415; forest, 433; hay, 418; oats, 405; pasture, 410; plowed fields, 403; shrubs, 421 ; soybeans, 402 ; wheat, 401 Sparrow, Le Conte's 462, 463 as species in fallow fields, 451 ; small grain, 448 Sparrow, savannah, 462, 496, 496 habitat preferences, 513 as species in alfalfa, 423 ; clover, 420, 421, 422, 424; corn, 446; fallow fields, 415; grassland, 413; hay, 411, 424; marsh, 425; oats, 405; pasture^ 410, 412, 412; shrubs, 426, 428; small grain, 448; soybeans, 402, 441 Sparrow, song, 462, 463, 499-500, 508 habitat preferences, 513, 514 as species in clover, 421, 422; corn, 399, 445, 526 Illinois Natural History Survey Bulletin Vol. 28. Art. 3 44b\ fallow fields, 4Sl , 452; forest, 432, 453, 4SS\ grassland, 41i\ hay, 417, 453; marsh, 425 \ oats, 405; orchard, 429; pas- ture. 410, 450; shrubs, 426, 42S, 454; small grain, 44S; urban residential areas, 436; wheat, 407, 449 Sparrow, swamp, 462, 508 habitat preferences, 514 as species in alfalfa, 423; fallow fields, 451, 452; forest, 455; grassland, 413; hay, 417; marsh, 425; shrubs, 427, 454; small grain, 448 Sparrow, tree, 462, 463, 498 habitat preferences, 514 as species in corn, 392, 445, 446, 446; fallow fields, 451, 452; forest, 453, 455; hay, 453 pasture, 450, 452 ; plowed fields, 447 shrubs, 453, 454; small grain, 44S, 449 wheat, 449, 450; woodland, 392 Sparrow, vesper, 462, 497 habitat preferences, 513 as species in alfalfa, 423, 424 ; clover, 421, 424; corn. 39S, 400; hay, 417; oats, 405; orchard, 429; pasture, 410; shrubs, 426, 42S; soybeans, 401, 402 Sparrow, white-crowned, 462, 463 habitat preferences, 514 as species in fallow fields, 451 ; shrubs, 454 Sparrow, white-throated, 462 habitat preferences, 514 as species in corn, 445; fallow fields, 451; forest, 455; shrubs, 454 Species annotated list of, 463—500 definition of common, 387 habitat preferences of common, 513, 514 Starling, 461, 463, 465, 473, 474, 475, 486-7, 508, 511, 512, 513 habitat preferences, 513, 514 population (statewide), 503 population for all habitats in study, 507 as species in alfalfa, 423; clover, 421, 422, 424; commercial urban areas, 441; corn, 39S. 446; fallow fields, 415, 451; forest, 432, 455; grassland, 413; hay, 417, 453; marsh, 425; oats, 405; orchard, 429, 430; pasture, 410, 412, 450; plowed fields, 447 ; shrubs, 426, 453, 454; small grain, 448, 449; soybeans, 402; urban residential areas, 436, 437, 437; wheat, 407, 449; woodland, 434 Sturnella, 389 Sugar cane, 396 Swallow, bank, 460, 478 as species in grassland, 413; pasture, 410; shrubs, 426, 428 Swallow, barn, 460, 463, 478-9, 509 habitat preferences, 513 as species in alfalfa, 423; clover, 421, 422 corn, 398, 400, 400; fallow fields, 415 grassland, 413; hav, 417, 419; oats, 405 orchard, 429, 430, 430; pasture, 410, 412 shrubs, 427; soybeans, 402; wheat, 407 Swallow, cliff, 460, 478 as species in fallow fields, 415; oats, 405; shrubs, 427 ; wheat, 407 Swallow, rough-winged, 460, 463, 478 as species in clover, 421; fallow fields, 415; marsh, 425; pasture, 411; wheat, 407 Swallow, tree, 460, 463, 478 as species in corn, 399; marsh, 425; pas- ture, 411 Swift, chimney. 460, 463, 472-3, 503 habitat preferences, 513 as species in alfalfa, 423; clover, 421, 422 corn, 398; fallow fields, 415; forest, 433 hay, 417, 419; oats. 405; orchard. 429 pasture, 410; plowed fields, 403; shrubs, 427; soybeans, 402; urban residential areas, 436, 437; wheat, 407 Tables, types of, 388-9 Tanager, scarlet, 461 as species in forest, 433 ; shrubs, 427 Tanager, summer, 462 as species in clover, 421; forest, 432, 435; pasture, 411; woodland, 434 Teal, blue-winged, 459, 463 as species in marsh, 425 Tern, black, 459, 463 as species in hay. 417; marsh, 425 Thrasher, brown, Vd^, 463, 484, 484-5, 505 habitat preferences, 513 population (statewide), 508 population for all habitats in study, 507 as species in alfalfa, 423; clover, 421, 422; corn, 398; fallow fields, 415; forest, 432, 436; hay, 417, 419; marsh, 425; oats, 405; orchard, 429, 430; pasture, 410; plowed fields, 403; shrubs, 424, 426, 428; urban residential areas, 436; wheat, 407; wood- land, 434 Thrush spp., 485 Thrush, hermit, 460, 463 as species in shrubs, 454, 455 Thrush, Swainson's, 460, 463 Thrush, wood, 460, 485 as species in forest, 432, 435, 435, 436; shrubs, 426, 427; urban residential areas, 436; woodland, 434 Timothy, 416 acreage in state, 441 Titmouse, tufted, 460, 462, 482-3 habitat preferences, 513, 514 range extension, 509 as species in corn, 445, 446; forest, 432, 435, 453, 455; orchard, 429, 430, 430; pasture, 411; shrubs, 426, 427, 454; urban resident- ial areas, 436; wheat, 449; woodland, 392, 434 Towhee, rufous-sided, 462, 462 habitat preferences, 513 as species in corn, 398; fallow fields, 415; forest, 432, 435, 455; orchard, 429; pas- ture, 411 ; shrubs, 424, 426, 427, 454; urban residential areas, 436; woodland, 434 U Upland plover, 459, 463, 467, 468-9, 505, 506 habitat preferences, 513 as species in alfalfa, 423 ; corn, 398 ; clover 421, 422; fallow fields, 415; hay, 417, 419 oats, 405; pasture, 410; plowed fields, 403 soybeans, 402; wheat, 407 October, 1963 Graber & Graber: Bird Populations ix Illinois 527 Urban residential areas (urban areas, resi- dential areas), 401, 424, 430, 436-7, 438, 438, 439, 439, 440, 443, 458, 466, 469, 470, 471, 472, 473, 475, 479, 480, 481, 482, 483, 484, 485, 487, 488, 489, 491, 492, 493, 494, 498, 502, 503, 504, 507, 508, 509, 511, 512, 513, 515 acreage censused, 396, 436 acreage in state, 3SS, 441, 502, 511, 512 avifauna of, 436 bird populations in, 441, 511, 512 common species in, 437 Urban commercial areas, bird populations in, 441 Vegetable crops {see also Garden crops), 386 Vireo, Bell's, 461, 463 range extension, 509 as species in pasture, 411 ; shrubs, 426, 427 Vireo, red-eyed, 393, 461, 463 as species in forest, 432, 43 5; pasture, 411; shrubs, 427 \ urban residential areas, 436 \ woodland, 434 Vireo, warbling, 461 as species in forest, 433 \ shrubs, 427; urban residential areas, 436 Vireo, white-eyed, 461 as species in forest, 432, 43 5; shrubs, 426; woodland, 434 Vireo, yellow-throated, 461 , 463 as species in forest, 433; woodland, 434 Vulture, black, 459, 463 as species in pasture, 450 Vulture, turkey, 459, 464, 483 habitat preferences, 514 range extension, 509 as species in corn, 39S, 445; forest, 433, 455; hay, 41S, 453; pasture, 411, 450; small grain, 44S ; soybeans, 402; wheat, 449 W \^'arbler spp., 487 Warbler, black and white, 461 as species in forest, 433 Warbler, cerulean, 461, 463 as species in forest, 432; woodland, 434 Warbler, chestnut-sided, 461 , 463 Warbler, hooded, 461, 463 as species in forest, 433 Warbler, Kentucky, 461, 463 as species in forest, 432, 435; shrubs, 427; woodland, 434 \^'arbler, magnolia, 461, 463 Warbler, myrtle, 461 as species in forest, 455; shrubs, 454 Warbler, palm, 461, 463 Warbler, parula, 461 as species in forest, 433 ; shrubs, 427 Warbler, pine, 461, 463 Warbler, prairie, 461, 463, 510 as species in shrubs, 426, 427 Warbler, prothonotary, 461 as species in forest, 432; shrubs, 427 Warbler, Swainson's, 461, 463 ^^^arbler, worm-eating, 461, 463 as species in forest, 432; woodland, 434 Warbler, yellow, 461 as species in forest, 433; orchard, 429, 430; shrubs, 427 Warbler, yellow-throated, 461 , 463 Waterthrush, Louisiana, 461 as species in forest, 433 Waxwing, cedar, 461, 463 as species in pasture, 450; shrubs, 454 Weather (climate), 384, 393-6, 394, 395, 442, 458, 464, 471, 478, 486, 498, 500, 508, 512 Weeds, 401, 413, 424, 449, 505 Wetlands [see also Marsh), 424, 501 Wheat (wheat fields), 407-8, 438, 438, 439, 439, 443, 444, 448, 449-51, 456, 466, 469, 470, 471, 472, 474, 475, 478, 479, 480, 484, 488, 490, 491, 492, 493, 494, 495, 496, 497, 499, 509, 514 acreage censused, 396, 406, 407 , 443, 449 acreage in state, 388, 440, 457 avifauna of, 407, 449 bird populations in, 440, 442, 457 common species in, 406 statistical data on populations in, 406 Whip-poor-will, 460, 463 as species in forest, 433; shrubs, 427 Woodcock, American, 459, 463, 467 as species in pasture, 411 Woodland (woods, woody habitats; see also Forest), frontispiece, 386, 389, 393, 424, 431, 433, 436, 439, 440, 453, 456, 457, 464, 467, 476, 479, 481, 482, 483, 484, 491, 493, 494, 495, 498, 507, 511, 512 acreage in state, 441 bird populations in, 392, 392, 441 common species in, 434 Woodpecker, downy, 460, 462, 473, 475-6 habitat preferences, 513, 514 as species in corn, 399, 445, 446 ; fallow fields, 415, 451; forest, 432, 435, 453, 455; hay, 418, 453; pasture, 411, 450; plowed fields, 403; small grain, 448; shrubs, 426, 454; urban residential areas, 436; wood- land, 392, 434 Woodpecker, hairy, 460, 463, 473, 475, 503 habitat preferences, 514 as species in fallow fields, 451 ; forest, 432, 453, 455; pasture, 411, 450; shrubs, 454; woodland, 392, 434 Woodpecker, pileated, 460, 463, 473 as species in forest, 433, 455 Woodpecker, red-bellied, 460, 462, 473, 474, 503 habitat preferences, 514 range extension, 509 as species in corn, 445, 446; fallow fields, 451, 452; forest, 432, 453, 455; pasture, 411, 450; shrubs, 426, 454; small grain, 448; soybeans, 447; woodland, 392, 434 Woodpecker, red-headed, 460, 462, 473, 474-5, 505, 512 habitat preferences, 513, 514 population (statewide), 503 population for all habitats in study, 507 as species in clover, 421 ; corn, 398, 400, 445; fallow fields, 415; forest, 432, 436, 453, 455; grassland, 413; hay, 417, 419; oats, 405; orchard, 429, 430; pasture, 410; plowed fields, 403; shrubs, 426, 427; uj- ban residential areas, 436; wheat, 40/; woodland, 434 Illinois Natural History Survey Bulletin Vol. 28, Art. 3 Wren, Bewick's, 460 as species in corn, 399 \ fallow fields, 415; forest, 432 \ orchard, 429, 430 \ pasture, 410\ plowed fields. 403 \ shrubs, 426 Wren, Carolina, 460 as species in corn, 399, 445, 446 ; fallow fields, 415, 451 \ forest, 432, 453, 455 \ or- chard, 429; pasture, 411; shrubs, 426, 427, 454; urban residential areas, 436; woodland, 392, 434 Wren, house, 393, 460, 463 habitat preferences, 513 as species in forest, 432; orchard, 429, 430, 430; pasture, 410; shrubs, 426; urban resi- dential areas, 436; woodland, 434 Wren, long-billed marsh, 460, 463 as species in fallow fields, 451; marsh, 425 Wren, short-billed marsh, 460 as species in grassland, 413; hay, 417; marsh, 425 Wren, winter, 460 as species in forest, 455 Yellow-throat, 461, 463, 487-8 habitat preferences, 5l3 as species in alfalfa, 423; clover, 421; corn, 39S; fallow fields, 415; forest, 432; hay, 417; marsh, 425; oats, 405; orchard, 429, 430; pasture, 410; shrubs, 426, 427, 428 \ wheat, 407 Zonotrichia spp. in shrubs, 454 Some Publications of the Illinois Natural History Survey BULLETIN Volume 27, Article 4.—Food Habits of Migra- tory Ducks in Illioois. By Harry G. Ander- son. August, 1959. 56 pp., frontis., 18 figs., bibliog. 50 cents. V'olume 27, Article 5.—Hook-and-Line Catch in Fertilized and Unfertilized Ponds. By Donald F. Hansen, George W. Bennett, Robert J. Webb, and John M. Lewis. August, 1960. 46 pp., frontis., 11 figs., bibliog. Single copies free to Illinois residents; 25 cents to others. Volume 27, Article 6.—Sex Ratios and Age Ratios in North American Ducks. By Frank C. Bellrose, Thomas G. Scott, Arthur S. Hawkins, and Jessop B. Low. August, 1961. 84 pp., 2 frontis., 23 figs., bibliog. $1.00. (Make check payable to University of Illi- nois ; mail check and order to Room 279, Nat- ural Resources Building, Urbana, Illinois.) Volume 28, Article 1.—The Amphibians and Reptiles of Illinois. By Philip W. Smith. November, 1961. 29S pp., frontis., 252 figs., bibliog., index. $3.00. Volume 28, Article 2.—The Fishes of Cham- paign County, Illinois, as Affected by 60 Years of Stream Changes. By R. Weldon Larimore and Philip W. Smith. March, 1963. 94 pp., frontis., 70 figs., bibliog., index. 50 cents. CIRCULAR 39.—How to Collect and Preserve Insects. By H. H. Ross. July, 1962. (Sixth printing, with alterations.) 71 pp., frontis., 79 figs. Single copies free to Illinois residents; 25 cents to others. 47.—Illinois Trees and Shrubs: Their Insect Enemies. By L. L. English. March, 1962. (Second printing, with revisions.) 92 pp., frontis., 59 figs., index. Single copies free to Illinois residents; 25 cents to others. 48.—Diseases of Wheat, Oats, Barley, and Rye. ByG. H. Boewe. June, 1960. 159 pp., frontis., 56 figs. Single copies free to Illinois resi- dents; 25 cents to others. 49.—The Dunesland Heritage of Illinois. By Herbert H. Ross. (In cooperation with Illi- nois State Department of Conservation.) August, 1963. 28 pp., frontis., 16 figs., bibliog. BIOLOGICAL NOTES 38.—Ectoparasites of the Cottontail Rabbit in Lee County, Northern Illinois. By Lewis J. Stannard, Jr., and Lysle R. Pietsch. June, 1958. 20 pp., 14 figs., bibliog. 39.—A Guide to Aging of Pheasant Embryos. By Ronald F. Labisky and James F. Opsahl. September, 1958. 4 pp., illus., bibliog. 40.—Night-Lighting: A Technique for Cap- turing Birds and Mammals. By Ronald F. Labisky. July, 1959. 12 pp., 8 figs., bibliog. 41.—Hawks and Owls: Population Trends From Illinois Christmas Counts. By Richard R. Graber and Jack S. Golden. March. 1960. 24 pp., 24 figs., bibliog. 42.—Winter Foods of the Bobwhite in Southern Illinois. By Edward J. Larimer. May, 1960. 36 pp., 11 figs., bibliog. 43.—Hot-Water and Chemical Treatment of Illinois-Grown Gladiolus Cormels. By J. L. Forsberg. March, 1961. 12 pp., 8 figs., bib- Hog. 44.—The Filmy Fern in Illinois. By Robert A. Evers. April, 1961. 15 pp., 13 figs., bibliog. 45.—Techniques for Determining Age of Rac- coons. By Glen C. Sanderson. August, 1961. 16 pp., 8 figs., bibliog. 46.—Hybridization Between Three Species of Sunfish {Lepomis). By William F. Childers and George W. Bennett. November, 1961. 15 pp., 6 figs., bibliog. 47.—Distribution and Abundance of Pheasants in Illinois. By Frederick Greeley, Ronald F. Labisky, and Stuart H. Mann. March, 1962. 16 pp., 16 figs., bibliog. 48.—Systemic Insecticide Control of Some Pests of Trees and Shrubs—A Preliminary Report. By L. L. English and Walter Hart- stirn. August, 1962. 12 pp., 9 figs., bibliog. 49.—Characters of Age, Sex, and Sexual Ma- turity in Canada Geese. By Harold C. Han- son. November, 1962. 15 pp., 13 figs., bibliog. 50.—Some Unusual Natural Areas in Illinois and a Few of Their Plants. By Robert A. Evers. July, 1963. 32 pp., 43 figs., bibliog. MANUAL 4,—Fieldbook of Illinois Mammals, By Donald F. Hoflrmeister and Carl O. Mohr. June, 1957. 233 pp., color frontis., 119 figs., glos- sary, bibliog., index. $1.75. List of available publications mailed on request Single copies of Illikois Natural History Survey publications for which no price is listed will be furnished free of charge to individuals until the supply becomes low, after which a nominal charge may be made. More than one copy of any free publication may be obtained without cost by educational institutions and official organizations within the State of Illinois; prices to others on quantity orders of these publications will be quoted upon request. Address orders and correspondence to the Chiefs Illinois Natural History Survey, Natural Resources Building, Urbana, Illinois Payment in the form of money order or check made out to State Treasurer of Illinois, Springfield, Illinois, must accompany requests for those publications on which a price is set. a; I