Bulletin ILLINOIS NATURAL HISTORY SURVEY jiUll&TVtl Printed by Authority of the State of Illinois Sex Ratios and Age Ratios in North American Ducks FRANK C. BELLROSE THOMAS G. SCOTT ARTHUR S. HAWKINS JESSOP B. LOW STATE OF ILLINOIS Otto Kerner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION William Sylvester White, Director NATURAL HISTORY SURVEY DIVISION Harlow B. Mills, Chief NAIUKAL ILLINOIS NATURAL HISTORY SURVEY Bulletin Volume 27, Article 6 Printed by Authority of August, 1961 the State of Illinois Sex Ratios and Age Ratios in North American Ducks FRANK C. BELL ROSE THOMAS G. SCOTT ARTHUR S. HAWKINS JESSOP B. LOW STATE OF ILLINOIS Otto Kerner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION William Sylvester White, Director NATURAL HISTORY SURVEY DIVISION Harlow B. Mills, Chief Urbana, Illinois STATE OF ILLINOIS Otto Kerner, Governor DEPARTMENT OF REGISTRATION AND EDUCATION William Sylvester White, Dirtctor i BOARD OF NATURAL RESOURCES AND CONSERVATION William Sylvester White, Chairman; A. E. Emerson, Ph.D.. Biology; Walter H. Newhouse, Ph.D., Geology; Roger Adams, Ph.D., D.Sc, Chemistry; Robert H. Anderson, B.S.C.E., Etigineering; W. L. Everitt, E.E., Ph.D., Representing the President oj the University oj Illinois; Delyte W. Morris, Ph.D., President oj Southern Illtnois University NATURAL HISTORY SURVEY DIVISION, Urbona, Illinois SCIENTIFIC AND TECHNICAL STAFF Harlow B. Mills, Ph.D., Chief Bessie B. East, M.S., Assistant to the Chief Section of Economic Entomology Geor<;e C. Decker, Ph.D., Principal Scientist and Head J. H. Bigger, M.S., Entomologist L. L. English, Ph.D., Entomologist W. H. Llckmann, Ph.D., Entomologist Willis N. Bruce, Ph.D., Entomologist John P. Kramer, Ph.D., Associate Entomologist Richard J. Dysart, Ph.D., Associate Entomologist Ronald H. Meyer, M.S., Assistant Entomologist Reginald Roberts, M.S., Technical Assistant Ja.mes W. Sanford, B.S., Technical Assistant Earl Stadelbacher, B.S., Technical Assistant William C. Moye, M.S., Technical Assistant Sue E. Watkins, Technical Assistant H. B. Petty, Ph.D., Extension Specialist in Entomology* Stevenson Moore, III, Ph.D., Extension Specialist in Entomology* Zenas B. Noon, Jr., M.S., Research Assistant* Clarence E. White, B.S., Instructor in Entomology Extension* CosTAS Kouskolekas, M.S., Research Assistant* Amal Chandra Banerjee, M.S., Research Assistant* Victor T. Williams, B.S., Research Assistant* Section of Faunistic Surveys and Insect Identification H. H. Ross, Ph.D., Principal Scientist and Head Milton W. Sanderson, Ph.D., Taxonomist Lewis J. Stannard, Jr., Ph.D., Taxonomist Philip W. Smith, Ph.D., Associate Taxonomist Leonora K. Gloyd, M.S., Assistant Taxonomist H. B. Cunningham, M.S., Assistant Taxonomist Ruth P. Cash, Technical Assistant John M. Kingsolver, Ph.D., Research Associate Edward O. Moll. Research Assistant John D. Unzicker, Research Assistant Talaat K. Mitri, M.S., Research Assistant* Section of Aquatic Biology George W. Bennett, Ph.D., Aquatic Biologist and Head William C. Starrett. Ph.D., Aquatic Biologist R. W. Larimore, Ph.D., Aquatic Biologist David H. Buck. Ph.D., Associate Aquatic Biologist Robert C. Hiltibran. Ph.D.. Associate Biochemist Donald F. Hansen, Ph.D., Associate Aquatic Biologist William F. Childers, M.S., Assistant Aquatic Biologist Marifran Martin, Technical Assistant Robert D. Crompton, Field Assistant RoLLiN D. Andrews. Ill, B.S., Field Assistant Larry S. Goodwin, Laboratory Assistant David J. McGinty. Field Assistant* Section of Aquatic Biology—continued Charles F. Thoits, 111, A.B., Field Assistant* Section of Applied Botany and Plant Pathology J. Cedric Carter, Pli.D., Plant Pathologist and Head J. L. Forsberg, Ph.D., Plant Pathologist G. H. BoEWE, M.S., Associate Plant Pathologist Robert A. Evers, Ph.D., Associate Botanist Robert Dan Neely, Ph.D., Associate Plant Pathologist E. B. Himelick, Ph.D., Associate Plant Pathologist Walter Hartstirn, Ph.D., Assistant Plant Pathologist D. F. Schoeneweiss, Ph.D., Assistant Plant Pathologist Anne Robinson, M.A., Technical Assistant Section of Wildlife Research Thomas G. Scott, Ph.D., Wildlije Specialist and Head Ralph E. Yeatter, Ph.D., Wildlije Specialist F. C. Bellrose, B.S., Wildlije Specialist H. C. Hanson, Ph.D., Associate Wildlije Specialist Richard R. Graber, Ph.D., Associate Wildlije Specialist Ronald F. Labisky, M.S., Associate Wildlije Specialiit Glen C. Sanderson, M.A., Associate Wildlife Specialiil Marjorie J. Schlatter, Technical Assistant D. G. Rose, B.S., Technical Assistant Howard Crum, Jr., Field Assistant Rexford D. Lord, D.Sc, Project Leader* Jack A. Ellis, M.S., Project Leader* Bobbie Joe Verts, M.S., Project Leader* Ralph J. Ellis, M.S., Project Leader* William L. Anderson, B.S., Assistant Project Leadei* James A. Harper, M.S., Assistant Project Leader* David A. Casteel, B.S., Assistant Project Leader* Gerald G. Montgomery, M.S., Research Associate* P. J. Rao, B.V.Sc, M.A., Research Assistant* Ann C. V. Holmes, B.S.. Research Assistant* T. U. Meyers, Research Assistant* Stuart H. Mann, B.S., Research Assistant* Richard W. Lutz, M.W.M., Research Assistant* Richard D. Andrews. M.S., Field Mammalogist* Keith P. Dauphin, Assistant Laboratory Attendant* Section of Publications and Public Relations James S. Ayars, B.S., Technical Editor and Head Blanche P. Young, B.A.. Assistant Technical Editor Edward C. Visnow, M.A., Assistant Technical Editor Wilmer D. Zehr, Assistant Technical Photographer Technical Library Ruth R. Warrick, B.S., B.S.L.S., Technical Librarian Nell Miles, M.S., B.S.L.S., Assistant Technical Librarian CONSULTANTS; Herpetolocy, Hobart M. Smith, Ph.D., Professor of Zoology. University of ///inou; Parasitology, Norman D. Levine, Ph.D., Professor of Veterinary Parasitology and of Veterinary Research, University of Illinois; Wildlife Research, Willard D. Klimstra, Ph.D., Professor of Zoology and Director of Co-operative Wildlife Research, Southern Illinois University. •Employed on co-operative projects with one of several agencies: University of Illinois, Illinois Agricultural Extension Service, Illinois Department of Conservation, National Science Foundation, United States Department s old have been successfully sexed by this method. In the study reported here, trapped or bagged ducks that could not be readily sexed by plumage or by bill color were sexed by cloacal characters. Sampling Populations for Sex Ratios In the present study, several methods were used to sample waterfowl popula- tions for sex ratios. These were ( 1 ) ex- amination of trapped ducks, (2) inspec- tion of ducks in hunters' bags, (3) obser- vation of ducks in the field, and (4) ex- amination of disease victims. In endeavor- ing to determine the true sex ratios exist- ing among ducks in nature, we found that certain biases were implicit in each method. Biases in some methods were such that they could be corrected or ad- justed to the extent that fairly valid ra- tios could be derived. Following is a review of the four meth- ods used in sampling duck populations for sex ratios, the advantages of these methods, and the disadvantages. Examination of Trapped Ducks.— From the start of trapping and banding Table 1.—Drake percentages in mallards trapped and banded at the Chautauqua National Wildlife Refuge, near Havana, Illinois, and in year-of-banding recoveries, 1939-1944 and 1947—1950. Preponderance of drakes or hens recovered is indicated by differences in per- centage points: + for drakes, — for hens. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 397 operations in 1939 at the Chautauqua Na- tional Wildlife Refuge, near Havana, in Mason County, Illinois, records were kept of the sex of each duck that was trapped and banded. In all of these records, the relative numbers of drakes among the mallards and black ducks were so high as to arouse suspicion that the baited, fun- nel-type traps being used were selective for drakes, tables 1 and 2. At McGinnis Slough, in Cook County, the relative numbers of drakes among mallards and black ducks taken in similar traps were somewhat lower, tables 3 and 4, but they were high enough to indicate that the traps tended to take disproportionate numbers of drakes. Drakes made up about three-fourths of the mallards taken in banding traps at Lake ( hautauqua in the years 1939-1944 and 1947-1950, table 1. Evidence that, among mallards, the drakes are trapped much more readily than the hens is found by comparing figures derived from trap- ping and banding (73.3 per cent drakes, table 1 ) with figures derived from inspec- tion of hunters' bags (56.5 per cent drakes for the years 1939-1950 in table 13, or 53.8 per cent drakes after a correction fac- tor of 1.05 has been applied to compen- sate for hunter preference for drakes). Mallards entered the Lake Chautauqua traps at the rate of 1.4 drakes to 1 hen. The use of data derived by one method to check on the data derived by another is discussed in the section on inspection of hunters' bags. Further evidence that mallard drakes are trapped much more readily than the hens is found by comparing the relative numbers of birds of each sex that were re- trapped in the same season at two Illinois Table 3.—Drake percentages in mallards trapped and banded at McGinnis Slough, Cook County, Illinois, and in year-of-banding recoveries, 1941—1947. Preponderance of drakes or hens recovered is indicated by differences in percentage points: + for drakes, — for hens. 398 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 banding stations, tables 5 and 6. Chi- square tests disclosed that the relative number of drakes retrapped was signifi- the sexes in proneness to enter traps. Haw- kins found in banding blue-winged teals near the Pas, Manitoba, in 1951 that 39.0 Table 5.—Number of drake and hen mallards trapped and banded, and number and per cent of each ^roup retrapped at least once in the same season, at the Chautauqua National Wildlife Refuge, near Havana, Illinois, 1940 and 1941. Sex selectivity of baited traps is indi- cated by the ratio of drakes to hens among retrapped ducks. August, 1961 Bellrose et ah: Sex Ratios and Age Ratios 399 traps increased as the drake percentage in the population increased (indicated by bag checks, fig. 2). In the mallard and the black duck, dif- ferences in behavior may contribute to dif- ferences in numbers between males and females trapped or retrapped. One differ- blind near the traps on Lake Chautauqua showed that, when mallards were massed around the traps, the drakes were more forceful than hens in pushing their way into the traps. Chi-square tests of data in tables 1, 2, 3, and 4 indicate that in both the mallard 80 75 70 65 60 55 50 45 Trap Cotches 2nd 3rd 4th OCTOBER 1st 2nd 3rd NOVEMBER 4th 1st 2nd DECEMBER 3rd Fig. 2.—Week-to-week changes in the drake percentage of the autunnn flight of mallards in Illinois, as indicated by two sampling methods: checks of mallards in hunters' bags and inspec- tion of mallards caught in banding traps. Bag data are for the Illinois River valley, 1939-1949; trap data are for Lake Chautauqua, 1939-1944 and 1947. ence in behavior is the greater aggressive- ness of the drakes; this may occur because of differences in food demands during the fall. Studies on food consumption of penned wild mallards (Jordan 1953:122) revealed that, during the fall and winter, drakes consumed 15 per cent more food than did hens. Observations made from a and the black duck the propensity of drakes to enter traps was significantly greater at Lake Chautauqua than at Mc- Ginnis Slough. The population density was much greater at Lake Chautauqua than at McGinnis Slough. Consequently, the competition for bait at trap sites was greater, the aggressiveness of drakes was 400 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 I greater, and the trap catch of drakes was greater at Lake Chautauqua than at Mc- Ginnis Slough. Not all traps have been found selective for drakes. Merrill C Hammond, biolo- gist of the U. S. Fish and Wildlife Serv- ice, in an unpublished report prepared in 1949, stated that he captured more hens than drakes in a gate- type trap placed on shore adjacent to marsh vegetation in the Lower Souris National Wildlife Refuge in north-central North Dakota. He spec- ulated that because of nesting activity hens were more accustomed than drakes to walking on land through tall vegeta- tion ; therefore, they would enter a trap on the shore more readily than drakes. Supporting evidence for Hammond's speculation was obtained by Hawkins at Delta, ALinitoba, in 1950. He found that in two funnel-type traps placed only a few yards apart, one in the water and the other on land, the trap in water captured 2.2 drake mallards per hen, whereas the trap on land captured only 1.5 drake mal- lards per hen. Inspection of Hunters' Bags.—In- spection of ducks in hunters' bags in fall and early winter for obtaining sex ratio data was found to have some advantages. Late-molting adult drakes can be sep- arated from hens, which they resemble during the eclipse molt, and the sexes of juveniles can be distinguished; compari- sons can then be made between sex ratios of adults and those of juveniles. Avail- able data indicate that most sex ratios de- rived from inspection of hunters' bags are only slightly biased, usually in favor of drakes. Tendencies for hunters to bag propor- tionately more ducks of one sex than those of the other depend ( 1 ) partly upon the chronology of migration of the ducks, (2) partly upon the preferences of hunters, and (3) partly upon hunting conditions and upon skill of hunters. Differences in chronology of migration may expose birds of one of the sexes to a greater number of hunters or make them more vulnerable to hunting than birds of the other sex. A striking example of the relationship between the chronology of migration and shooting pressure was found in the red- head. Adult drake redheads move from their breeding grounds in southern Mani- toba to more northern marshes for molt- ing, while the hens remain on the breed- ing grounds, according to Milton W. Weller in an unpublished report prepared at the University of Missouri in 1954. Because bag checks showed that adult drakes comprised only a small proportion of a large kill of redheads made in south- ern Manitoba, Weller deduced that the southward migration of adult drake red- heads involved much longer flights than the migration of adult hens. Evidence suggesting that the migration of adult drake redheads to the wintering grounds consists of long flights is given by band re- coveries reported by Cartwright & Law (1952:11), who showed a much lower year-of-banding recovery rate for these birds than for juvenile males or for fe- males. Geis (1959:256-7) found that, among canvasbacks, adult hens and juveniles of both sexes had a higher percentage of band recoveries early in the hunting sea- son than did adult drakes, while adult drakes had a higher percentage of band recoveries on the wintering grounds than did either adult hens or juveniles. Band recovery rates indicate that adult drakes in the canvasback, like those in the red- head, make longer flights along migra- tion routes than do adult hens. That hunters may prefer to shoot ducks of one sex rather than those of the other is shown by interviews with hunters and by analysis of data on duck kill. It seems logical to assume that hunters, faced with a species having a drake more brilliantly colored than the hen and given an equal opportunity at birds of each sex, would pick the more brightly colored bird, as Mcllhenny (1940:87) suggested. In Illinois, the mallard and the black duck have similar habits and behavior. On the wing, the black duck drake is iden- tical in appearance to the hen, whereas the mallard drake, during most of the Illi- nois hunting season, is readily distinguish- able from the hen. That under certain circumstances hunt- ers demonstrate a preference for drakes that are brightly colored and readily dis- tinguishable from hens may be shown through study of the results of banding operations at Lake Chautauqua, 1939- August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 401 1944 and 1947-1950, tables 1 and 2. The drake percentage among the birds trapped can be compared with the drake percentage among the birds represented by band recoveries. Too few black ducks were banded to permit valid comparisons each year ; however, when the data for the black duck were totaled for the 10 years of study, no marked hunter prefer- ence for drakes was evident in this species. In the case of the mallard, the preponder- ance of drakes among the banded ducks recovered indicated a consistent year-to- year tendency for hunters to select drakes to a somewhat greater extent than hens, there being only 1 year (1947) in which hunter preference for drakes was not evi- dent. In the period 1939-1950, the drake percentage among 2,128 mallards reported shot in the year they were banded (76.8 per cent) was shown by a chi-square test to be significantly greater than the drake percentage among 38,735 mallards that were trapped and banded (73.3 per cent), table 1. These percentage figures indi- cate that drakes were 1.05 times as likely to be taken by hunters as were hens. This estimate of the greater likelihood of mal- lard drakes being taken by hunters can be used as a correction factor to com- pensate for hunter preference in calcula- tions employing other data involving the same species, the same area, the same pe- riod of )^ears, and the same time of year. The ducks represented in table 13 were mallards shot by hunters in approximately the same area and times of year as those represented in table 1. Calculations based on data in table 13 show that for 1939- 1950, the period of years covered in table 1, 56.5 per cent of the mallards checked in hunters' bags were drakes. Allowance can be made for hunter preference for drakes by applying the correction factor 1.05 to this percentage figure. The result is 53.8 per cent, which is believed to represent the average drake component of the fall popu- lations of mallards in the Illinois River valley in the period 1939-1950. That the degree to which hunters se- lect drakes rather than hens may be in- fluenced by hunting conditions and by the skill of the hunters, as well as by per- sonal preferences of hunters, can be shown by comparison of band recovery data from mallards banded at Lake Chau- tauqua with similar data from mallards banded at McGinnis Slough, tables 1 and 3. Bandings at Lake Chautauqua were made in the heart of the duck hunting club area of Illinois, where ducks were comparatively numerous and where hunt- ers, many of them experienced shots, could afford to be selective of their targets. Bandings at McGinnis Slough were in an area where competition for ducks was much keener than near Lake Chautauqua and where hunters tended to shoot at ex- treme ranges. Analysis of band recovery data for mallards banded at McGinnis Slough showed no hunter preference for drakes, table 3. Even hunters who have access to the best shooting areas vary from year to year in the degree to which they choose drakes. At Stuttgart, Arkansas, in 1946, when hunting conditions were unfavorable be- cause high water had dispersed the ducks through the swamps and when the bag limit was seven ducks, drakes comprised only 51.0 per cent of 3,350 mallards checked in hunters' bags. In the 1947 season, when hunting was much better in the Stuttgart region and the bag limit was only four, drakes comprised 59.5 per cent of the 3,317 mallards checked. Of the Stuttgart region in the hunting season of 1945-46, Hawkins, Bellrose, & Smith (1946:398) wrote: "Hunting is so good in the Grand Prairie area that the better hunters can, and a few do, deliberately select drakes." In the sample of bagged ducks they inspected, 55.8 per cent were drakes. Field Observations. — Observations on living ducks in the field are a means of providing sex data on large samples of many species. With such data, no com- pensation is needed for differences in trap and hunter selectivity. It is almost impos- sible, however, to make a sufficient num- ber of random counts to insure an ade- quate cross section of the population of a flyway or other large area. Field counts of the drakes and hens in duck popula- tions are more readily taken in late win- ter and early spring than at any other time. Early in the fall the juvenile and eclipse plumages make distinguishing be- tween the sexes difficult, and hunting activity at that time usually makes ducks 402 Illinois Natural History Survey Bulletin Vol. 27, Art. b Table 7.—Drake percentages in pintails, redheads, and lesser scaups observed in the field on the Lower Souris National Wildlife Refuge, North Dakota, 1948.* Species August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 403 checking the sex of 85 duck embryos that died, 419 ducklings that died from para- typhoid, and 70 survivors. Hochbaum (1944:51) similarly classified embryonic and hatched ducklings of the canvasback and found 344 males and 345 females. Secondary Sex Ratios.—The second- ary sex ratios found by Sowls (1955: 164) for four species of ducks are re- corded in table 8. Statistical analysis of the data, which are from a study at Delta, Manitoba, revealed that at hatching the sex ratios of mallard, pintail, redhead, and canvasback ducklings did not depart sig- nificantly from a 50:50 ratio. However, in each of the four species, males exceeded females in numbers; when the data for all four species were combined, there was a slight but statistically significant pre- ponderance of males. The findings sug- gest that the female embryos in these spe- cies were not as hardy as the embryos of the males. They are supported by the Table 8.—Male percentages found at hatch- ing of artificially incubated eggs of four duck species at Delta,* Manitoba, and one, the wood duck, in Illinois. Species 404 Illinois N.atural History Survey Bulletin Vol. 27, Art. 6 drive trapping and bait trapping, while those in Saskatchewan and Alberta were obtained by drive trapping only. Se.x ratios of ducklings in three of the four species trapped in Manitoba, table 9, showed relatively greater numbers of hens than of drakes. Statistical analysis showed that the pintails and blue-winged teals of Manitoba had highly significant excess numbers of hens. Of nine species of ducks trapped in Saskatchewan, only the baldpate {Mareca americana) had a significantly higher number of drakes, table 10. Of eight species of ducklings that were trapped in Alberta, table 11, seven had sex ratios that did not depart Table 12.—Drake percentages In ducks of nine species, juvenile and adult classes, checked in hunters' bags in Manitoba, 1946—1949. Species Juveniles Number Checked Per Cent Drakes Adults Number Checked Per Cent Drakes Mallard Gadwall Baldpate Pintail Green-winged teal Shoveler Redhead Canvasback Lesser scaup All species 6,473 339 822 1,145 257 342 1,110 2,116 558 13,162 53.2** 60.2** 51.0 NS 51.7 NS 57.2* 50.9 NS 51.0 NS 39.8** 47.1 NS 50.5 1,786 137 147 293 58 81 139 232 302 3,175 49.3 NS 43.1 NS 59.2* 38.6** 24.1** 32.1** 51.8 NS 49.1 NS 60.3** 48.7 NS :::: Not a significant departure from 50 per cent at the 0.05 probability level. *Signilicant departure from 50 per cent at the 0.05 probability level. •'Significant departure from 50 per cent at the 0.01 probability level. Table 13.—Drake percentages in mallards, juvenile and adult classes, checked in hunters' bags in Illinois, 1939-1955 and 1959. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 405 significantly from 50:50; the pintail had significantly more drakes. Among 419 captive wood duck duck- lings that died from paratyphoid in a hatchery at Barrington, Illinois, 51.5 per cent were females. Of 96 young wood ducks that died from other causes early in life, 48.8 per cent were females. Information on the sex ratios of juve- nile ducks 4 to 9 months old was ob- dent in the calculated sex ratios for juve- niles, tables 13 and 14. Highly significant deviations from a 50:50 sex ratio in the juvenile class occurred for the pintail, green-winged teal, and canvasback. The most marked deviation in the juvenile class was for the canvasback ; in this species the drake segment was 39.8 per cent of 2,116 juvenile birds inspected early in the fall in Manitoba, table 12, Table 14.—Drake percentages in ducks of nine species, juvenile and adult classes, checked in hunters' bags in Illinois, 1939—1949. Species Juveniles Number Checked Per Cent Drakes Adults Number Checked Per Cent Drakes Difference Between Adult (-f ) and Juvenile (— ) Percentages Black duck Gadwall Baldpate Pintail Green-winged teal Shoveler Ring-necked duck Canvasback Lesser scaup All species 371 613 1,128 2,281 399 516 717 352 841 7,218 51.7 NS 51.1 NS 51.5 NS 58.3** 60.9** 55.4* 53.8* 64.5** 54.2* 55.6** 194 182 416 1,200 160 110 190 171 441 3,064 70.6** 58.2* 61.8** 62.7** 57.5 NS 52.7 NS 51.0 NS 66.1** 61.0** 61.4** + 18 + 7 NS = Not a significant departure from 50 per cent at the 0.05 probability level. *Significant departure from 50 per cent at the 0.05 probability level. **Significant departure from 50 per cent at the 0.01 probability level. tained from the inspection of hunters' bags in Manitoba, Illinois, and other parts of the Mississippi Flyway. In Manitoba during early fall, the sex ratios for a group of juvenile ducks taken by hunters were nearly balanced, table 12. Four of the nine species rep- resented, the mallard, gadwall, green- winged teal, and canvasback, departed significantly from balanced sex ratios. The slight preponderance of males for the mallard (53.2 per cent males) was statistically significant because of the very large sample size. The gadwall and the green-winged teal had significantly more males than females, while the canvasback had significantly more females. In Illinois, drakes made up 49.3 per cent of 12,550 juvenile mallards in hunt- ers' bags inspected in the period 1939- 1950 and 50.4 per cent of 15,267 in- spected in the period 1939-1955 and 1959, table 13. Perhaps because of dif- ferences in migration schedules, consider- able differences among species were evi- and 64.5 per cent of 352 juvenile birds checked later in Illinois, table 14. When sex ratios were calculated for juveniles from many areas in the Missis- sippi Flyway for 1946-1948, tables 15-17, the effect of seasonal and regional varia- tions in the data appeared to be mini- mized. Deviations from a 50:50 sex ratio among juveniles were significant or highly significant statistically for only three spe- cies in 1946 and two species in 1948, ta- bles 15 and 17. In 1947, deviations from a 50:50 ratio in juveniles were significant for one species and highly significant for four of the species listed, table 16. The above data, obtained from trap- ping of ducks in the breeding season and from checking hunters' bags during the fall, indicate that the sex ratios in the tertiary or juvenile age class are close to 50:50. Local variations that exist appear to result from different seasonal move- ments of birds of the two sexes. Quaternary Sex Ratios.—Popula- tions of adult ducks normally show much 40b Illinois Natural History Survey Hulletin Vol. 27, Art. 6 larger drake segments than do those of juveniles. Exceptions are evident in the adult ducks shot by hunters in Manitoba, table 12. The data reveal for adult mal- lards, gadwalls, pintails, green-winged teals, shovelers, and canvasbacks in this area more hens than drakes. For pintails, green-winged teals, and shovelers, the ex- cess of hens was highly significant. This situation came about through the move- ment of many adult drakes from the area prior to the opening of the hunting sea- son. Of the species for which records are available, only baldpates, redheads, and lesser scaups showed more drakes than hens in hunters' bags in Manitoba. Statistical analysis of data obtained from inspection of adult ducks in hunters' bags to the south, in Illinois, revealed that in most years there were significantly' Table 15.—Drake percentages in ducks of 12 species, juvenile and adult classes, checked in hunters' bags in the Mississippi Flyway, 1946. Species Mallard Black duck Gadwall Baldpate Pintail Green-winged teal Blue-winged teal. Shoveler Redhead Ring-necked duck Canvasback Lesser scaup All species Juveniles Number Checked 5,350 966 474 462 681 360 411 380 806 416 1,663 510 12,479 Per Cent Drakes Adults Number Checked 47.5** 47.3 NS 49.7 NS 46.1 NS 54.9* 51.6 NS 46.9 NS 49.4 NS 52.4 NS 51.4 NS 45.1** 48.6 NS 48.3 3,593 215 249 119 426 157 122 125 204 113 208 232 J, 763 Per Cent Drakes 57.1** 68.3** 55.0 NS 60.5* 65.0** 52.2 NS 35.2** 42.4 NS 55.3 NS 55.7 NS 44.2 NS 51.7 NS 56.4 Difference Between Adult (-f) and Juvenile (— ) Percentages + 9.6 + 21.0 + 5.3 + 14.4 -f- 10.1 + 0.6 - 11.7 - 7. S.I NS = Not a significant departure from 50 per cent at the 0.05 probability level. •Significant departure from SO per cent at the 0.05 probability level. 'Significant departure from 50 per cent at the 0.01 probability level. Table 16.—Drake percentages in ducks of 12 species, juvenile and adult classes, checked in hunters' bags in the Mississippi Flyway, 1947. Species Juveniles Number Checked Per Cent Drakes Adults Number Checked Per Cent Drakes Difference Between Adult (+) and Juvenile (— ) Percentages Mallard Black duck Gadwall Baldpate Pintail Green-winged teal Blue-winged teal . Shoveler Redhead Ring-necked duck Canvasback Lesser scaup //// species 7,094 1,021 647 750 1,261 574 1,235 284 396 291 562 468 14,583 52.5** 49.9 NS 51.3 NS 48.4 NS 53.2* 62.2** 41.1** 50.7 NS 52.8 NS 46.4 NS 38.8** 46.4 NS 50.8 NS 2,604 398 208 236 437 173 360 56 91 85 143 310 5J01 60.8** 55.0 NS 63.5** 60.6** 53.8 NS 50.9 NS 3I.4NS 39.3 NS 35.2** 48.2 NS 61.5** 66.1** 56.8** + 8.3 + 5.1 + 12.2 -f 12.2 + 0.6 - 11.3 - 9.7 - 11.4 - 17.6 -f- 1.8 + 22.7 + 19.7 6.0 NS = Not a significant departure from 50 per cent at the 0.05 probability level. •Significant departure from 50 per cent at the 0.05 probability level. ••Significant departure from 50 per cent at the 0.0 1 probability level. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 407 more drakes than hens in the samples, ta- bles 13 and 14. Records on 9,725 adult mallards over a period of 12 years, 1939- 1950, revealed an average of 65.7 per cent drakes, with annual percentages ranging from 58.5 to 68.7 per cent; rec- ords on 11,637 adult mallards for a pe- riod of 18 years, 1939-1955 and 1959, re- vealed an average of 65.2 per cent drakes, with annual percentages ranging from 58.5 to 70.8, table 13. The adult class of nine other species of ducks in hunters' bags over an 11-year period, 1939-1949, con- tained 61.4 per cent drakes; annual per- centages ranged from 70.6 per cent drakes for the black duck to 51.0 per cent drakes for the ring-necked duck, table 14. Statistical analysis of data compiled from the inspection of adult mallards, gadwalls, baldpates, pintails, green- winged teals, shovelers, and redheads in hunters' bags in Utah over a period of 6 years, 1943-1944 and 1946-1949, table 18, revealed a highly significant greater number of drakes than hens for all spe- cies excepting the redhead. Data from the Mississippi Flyway for 3 years, 1946-1948, tables 15-17, indi- Table 17.—Drake percentages in ducks of 11 species, juvenile and adult classes, checked in hunters' bags in the Mississippi Flyway, 1948. Species Juveniles Number Checked Per Cent Drakes Adults Number Checked Per Cent Drakes Difference Between Adult (4-) and Juvenile (— ) Percentages Mallard Black duck Gadwall Baldpate Pintail Green-winged teal . Blue-winged teal. . Redhead Ring-necked duck . Canvasback Lesser scaup All species . 7,416 871 214 1,068 727 493 255 680 336 520 547 13,127 52.5** 47.2 NS 53.7 NS 49.5 NS 51.8 NS 55.6* 47.5 NS 46.6 NS 48.2 NS 48.5 NS 49.2 NS 51.2 NS 2,556 378 31 141 216 130 63 82 66 66 186 3,915 58.0** 59.0** 58.0 NS 50.3 NS 56.5 NS 49.2 NS 30.1** 51.2 NS 56.0 NS 43.9 NS 67.7** 58.1** + 5.5 + 11,8 + 4.3 + 0.8 + 4.7 - 6.4 - 17.4 + 4.6 4- 7.8 - 4.6 + 18.5 6.9 NS=:Not a significant departure from 50 per cent at the 0.05 probability level. *Significant departure from 50 per cent at the 0.05 probability level. **Significant departure from 50 per cent at the 0.01 probability level. Table 18.—Drake percentages in ducks of seven species, juvenile and adult classes, checked in hunters' bags in Utah, 1943, 1944, and 1946-1949. Species Juveniles Number Checked Per Cent Drakes Adults Number Checked Per Cent Drakes Difference Between Adult (+) AND Juvenile (— ) Percentages Mallard Gadwall Baldpate Pintail Green-winged teal Shoveler Redhead .4/1 species 2,027 1,679 2,352 4,230 2,828 2,480 734 16,330 52.3* 53.5* 52.2* 46.8* 58.0* 53.7* 57.3* 52.5* 2,350 1,955 1,183 6,499 4,183 1,674 214 18,058 62.3** 61.1** 61.5** 53.6** 72 9** 65!6** 48.6 NS 62.3** + 10.0 -t- 14.2 + 9.3 + 6.8 + 14.9 4- 11.9 - 8.7 9.9 NS=:Not a significant departure from 50 per cent at the 0.05 probability level. •Significant departure from 50 per cent at the 0.05 probability level. '•Significant departure from 50 per cent at the 0.01 probability level. 408 Illinois Natlral History Survey Bulletin Vol. 27, Art. 6 cate that adult drakes consistently, but not in all cases significantly, outnumbered adult hens in hunters' bajjs for mallards, black ducks, gadwalls, baldpates, pin- tails, and lesser scaups. By contrast, the records show that hens were more nu- merous than drakes among the blue- winged teals and shovelers inspected, and year-to-year variation was evident in sex ratios among green-winged teals, redheads, ring-necked ducks, and canvasbacks. Ta- bles 15-17 indicate the statistical signifi- cance of the departure of these sex ratios from balanced sex ratios. Seasonal Variations in Sex Ratios Sex ratios for many species of ducks were found to vary from week to week in any given area as the composition of the local population changed with arrival and departure of flocks containing varying numbers of drakes and hens. The sea- sonal changes in sex ratios were ascer- tained through data obtained from trap- ping, inspection of hunters' bags, field ob- servation, and tallies of victims of disease. Sex Ratios in Fall and Winter.— The sex ratios of the m.ost important spe- cies of ducks taken by hunters during the fall hunting season in areas from the breeding grounds to the wintering grounds are indicated in table 19. Sex ratios taken in southern Manitoba for the pintail, shov- eler, and canvasback suggest that large numbers of drakes make an early depart- ure from the heavily gunned marshes of Delta and Netley. This early movement may be initially either south or north, the direction depending somewhat upon the species. Information on the early flights of drake pintails, some of which arrive at the Gulf of Mexico in August, indicates that the initial movement of these birds is south. Records of large numbers of drake canvasbacks and redheads in north- ern Manitoba and Saskatchewan marshes suggest that these birds probably move north from their breeding grounds before they move south. In most species of ducks for which data are available, drakes made up a smaller proportion of the hunters' kill in Mani- toba than in three states to the south, North Dakota, Illinois, and Tennessee, table 19. These data indicate that in most species more drakes than hens left Mani- toba in advance of the hunting season there. A trend toward an increasing drake predominance from north to south was evident as far south as Tennessee. In all but two species for which data are available, the gadwall and shoveler, the predominance of drakes was greater in Tennessee than in Illinois. In Louisiana, a significantly greater number of hens than of drakes was evident in two species, the mallard and the pintail, and approxi- mately balanced sex ratios were evident in four species. In all six species it was ap- parent that more drakes than hens were Table 19.—Drake percentages in 12 species of ducks Species Mallard Black duck Gadwall Baldpate Pintail Green-winged teal. Shoveler Redhead Ring-necked duck. Canvasback Lesser scaup Ruddy duck Manitoba, 1946-1949 Number of Ducks 8,259 476 969 1,438 315 423 2,348 860 Per Cent Drakes 52.4 55.2 52.2 49.0 51.1 47.3 40.7 51.6 North Dakota, 1949 Number of Ducks 2.212 579 146 210 86 137 342 281 136 Per Cent Drakes 57.5 54.1 53.4 53.0 53.5 51.0 55.0 56.0 52.2 Illinois, 1939-1950 Number of Ducks 22,275 565 795 1,544 3,481 559 626 907 931 2,012 Per Cent Drakes 56.5 58.2 52.7 54.3 59.8 59.9 54.9 53.2 65.3 56.2 •Sources of data for the various regions: Manitoba, Delta Waterfowl Research Station; North Dakota, Hjelle mission (personal communication) ; Louisiana, Richard Yancey, Louisiana Wild Life and Fisheries Commission (per- Barber, Jr., North Carolina Wildlife Resources Commission (personal communication). August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 409 north of Louisiana during a large part of the hunting season. For all species of ducks e.xcept the shoveler, the differences in sex ratios among the various regions were statisti- cally significant. This conclusion must be taken with some reservations because the span of 3'ears involved was not the same for each of the various areas. Some of the observed differences could be due to time as well as geographic differences. Among adult mallards bagged in Illi- nois, 1939—1955, there was a steady in- crease in the drake segment of the fall population through the third week in No- vember, fig. 3. The ratio between the sexes then tended to stabilize for a period, followed by an increase in the drake seg- ment in the wintering population, usu- ally present in Illinois after the first week in December. In Utah, sex ratios of adult mallards bagged were relatively stable throughout the autumns of several years in which bag checks were recorded, fig. 4. Adult pintails bagged in Illinois and those bagged in Utah showed little varia- tion in sex ratios during the fall. Adult green-winged teals and shovelers bagged in Utah showed an increase in the drake segment as the season progressed, fig. 4. In only a few species do there appear to be dififerences in seasonal movement be- tween drakes and hens of the juvenile class. In Manitoba, the canvasback had an unusually large number of hens among the juveniles bagged, table 12; in Illinois, on the other hand, this species had an unusually large number of drakes among the juveniles bagged, table 14. The drake segment of the juvenile mallard popula- tion bagged in Illinois increased through the second week of November and then tended to stabilize, fig. 3. Sex ratios of ducks in the marshes ad- jacent to Great Salt Lake, Utah, have been quite variable from week to week and year to year in autumn. The week-to-week variation in sex ra- tios among ducks of these marshes is un- derstandable in view of the fact that in early summer the areas are the breeding grounds for ducks of many species, later a major molting area for transient pin- tails and green-winged teals, and still later one of the important migration areas for ducks in the Pacific Flyway. Chrono- logical differences in movement of vari- ous groups of ducks—those that breed in the area, early migrants that wing-molt in the area, and large numbers of fall migrants that rest there—have resulted in ever-changing sex ratios. Year-to-year variation in sex ratios is shown in data from the Bear River Mi- gratorv Bird Refuge at the north end of Great "Salt Lake (Van Den Akker & Wil- son 1951:379). In that area hens out- numbered drakes in 8 of 13 species in the period 1936—1940. However, during the hunting seasons in later years, 1943-1949, checked in hunters' 410 Illinois Natural History Survey Bulletin Vol. 27. Art. b at Ogden Bay, midway on the east side of Great Salt Lake, hens outnumbered drakes in only a few instances: in pin- tails 2 years and in redheads 1 year, table 20. When the statistical sifjnificance of the differences between the data for these \ears was investigated, the year-to-year fluctuations in sex ratios were found to be lOOpTIT highly significant for all species except the baldpate and the shoveler. Popula- tions that were top-heavy with drakes were observed in this same area before the hunting seasons of 1944 and 1950. Ducks that were victims of botulism in the Og- den Bay area showed that adult drakes were much more abundant than adult 15-22 23-31 OCTOBER 8-15 16-23 NOVEMBER 24-30 1-7 8-15 DECEMBER Fig. 3.—Drake-hen composition of the adult and juvenile segments of the autumn flight of mallards in Illinois, as indicated by data from checks of hunters' bags, in the autumns of 1939- j 1955. The drake segment of the juvenile mallard population increased through the second week in November and then became relatively stable. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 41: « Z-. 41. Illinois Natural History Survey Bulletin Vol. 27, Art. 6 early spring have revealed differences in the sequence of the northward mij^ration of drakes and hens of the same species. The sequence in the migration of drakes and hens varies with the region, table 24. In the Illinois River valley, tallies of drakes and hens in late winter and spring were compiled for the vears 1940-1946, fig. 5. A preponderance of drakes was most pronounced for the mallard, pintail, can- vasback, and ring-necked duck late in February. In the redhead and the lesser scaup, drakes predominated to the great- est extent in the second half of March ; in the baldpate, in the second half of April. Farther north in the Mississippi Fly- way, in Minnesota, Erickson (1943:27) observed changes in the drake and hen seg- ments of the populations during the spring migration periods of 1938-1940. Among blue-winged teals, in 2 of the 3 years, the relative number of drakes was consider- ably greater in the first than in the second of the two parts into which Erickson di- vided the migration period. Among shov- elers, in each of the 3 years, the relative number of drakes was greater in the sec- ond part than in the first part of the mi- gration period. Among lesser scaups, drakes predominated throughout the mi- gration period in each year, but to a lesser extent in the second part than in the first. Among ring-necked ducks, the sex ratios varied little between the two parts of each migration period or among the 3 years; the average male to female ratio for the 3 years was 1.36:1 in the first part and 1.43:1 in the second part of the migra- tion period. Near Minneapolis, in the spring of 1950, Nelson (1950:119) observed male to female ratios of approximately 1.3:1 Table 21.—Drake percentages in seven species of ducks, juvenile and adult classes, afflicted with botulism at Ogden Bay Bird Refuge, Utah, August 1 to September 29, 1944.* August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 413 a < 414 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 24.—Drake percentages in 10 species of ducks observed Species Mallard Baldpate Pintail Blue-winged teal . . Shoveler Redhead Ring-necked duck. Canvasback Lesser scaup Ruddy duck Cali- fornia, 1948-1951 p. ^ 3 OQ 1,039 432 362 671 370 371 ;UQ Oregon, 1946-1948 55.4 45.8 69.6 60.5 53.0 67.4 5,589 30 4,561 2,823 55.9 53.3 57.4 59.1 Wash- ington, 1943, 1944 1,652 4,999 622 101 316 911 Oh 50.7 53.3 52.2 53.5 67.7 59.8 North Dakota, 1939-1942, 1947-1950 202 911 173 554 000 805 63 826 401 ;UQ 51.7 57.2 52.7 55.5 53.7 54.8 57.1 62.6 64.0 64.7 Manitoba, 1939-1945 2,423 S8^^ c « <" J: a, 50.6 3,250 August, 196 416 Illinois N.vtural History Survey Bulletin Vol. 27, Art. 6 adults in which the testes had not reached recrudescence. Among pintails presumed to have died from fowl cholera in Texas in the first 4 months of 1948, the se.x ratio trend was the opposite of the trend among mallards, table 25, from a population predominantly drakes at the start of the period toward a balanced population at the end. The change in pintail sex ratios was not signif- icant at the 95 per cent level (X- = 10.4, 6 d.f.). Drakes were found to predom- inate in the pintail population along the Texas coast during the hunting season, table 19. It may be concluded that the pintail drakes tend to winter farther north than the hens but that most of the pintail population winters farther to the south, in Mexico, than does the mallard popu- lation. Sex Ratios in the Breeding Season. —Seasonal changes in sex ratios of ducks observed on the Manitoba breeding grounds in 1947 and 1949 are shown for various species in tables 26 and 27. In April, the first flights arriving on the breeding grounds showed, with minor ex- ceptions, a closer approach to a balance between the sexes than did subsequent populations on the breeding grounds, fig. 6. Somewhere between the mid-flyway areas and the breeding areas of southern Manitoba, late migration waves predom- inating in hens appeared to overtake early migration waves predominating in drakes. A tendency toward balanced sex ratios Table 26.—Drake percentages in seven species of ducks observed in four periods of the spring months along study transects on the Manitoba breeding grounds, 1947.* August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 417 among early arrivals on the breeding grounds evidently is observed in late March and early April on the Oka State Sanctuary in Russia, vv^here the first mal- lards to arrive are paired (Teplov & Kar- tashev 1958:160). The upward swing in the relative num- bers of drakes among the mallards and pintails seen by observers in early May, tables 26 and 27, soon after arrival of the ducks on the breeding areas of Manitoba, may be indicative of the rate at which hens leave their mates to incubate. By mid-July the relative number of drakes among ducks seen on potholes in southwestern Manitoba, table 27 and fig. 6, had noticeably decreased in all species —less in the lesser scaup and the blue- winged teal than in the other species. At this time, the drakes were evidently leav- ing the breeding areas for the lakes or marshes where they would enter the eclipse molt. A similar sequence in sex ratios was found in 1949 by I. G. Bue, then at the University of Minnesota, in ducks seen on stock ponds in western South Dakota, fig. 7. Between the first week of May 80 I- 70 60 50 40 30 20 10 - Pintail APRIL2I-25 APRIL 29- MAY 7 MAY 14 -JUNE 6 JULY 5-26 Fig. 6.—Periodic changes in the drake percentage in each of six species of ducks on a breeding grounds area near Minnedosa, Manitoba, April 21-July 26, 1949. Data were obtained from counts of living birds. 418 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 and the last, during the time pintail hens were leaving their mates to nest, the num- ber of drakes increased from 57 to 81 per cent of the pintails observed. An abrupt decrease in the relative number of pintail drakes took place in the first half of June when many of them were departing for areas in which to molt. Mallard drakes were about 2 weeks later than pintails in their departure to molt, and blue-winged teal drakes were about 2 weeks later than the mallard drakes. Sex ratios of ducks seen during the nest- ing period may provide useful informa- tion on the destruction of duck nests. When their nests are destroyed, hens re- turn to their waiting sites, where they can be seen by observers; this behavior results in an apparent increase in the rela- tive number of hens in the populations. L> nch (1948:26) presented evidence to show increases in the relative numbers of paired mallards and pintails seen on a study area in southern Saskatchewan late in May, 1947. These increases may have been attributable to heavy nest losses re- H 65 - I I I I I \ \ \ L J I 8 15 21 I APRIL 9 16 22 29 5 12 19 26 3 10 17 MAY JUNE JULY Fig. 7.—Periodic changes in the drake percentage in each of three species of ducks on stock ponds in western South Dakota, April 8-July 17, 1949. Data were obtained from counts of living birds and were provided by I. G. Bue, Commissioner, North Dakota Game and Fish Depart- ment, Bismarck, while at the University of Minnesota. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 419 suiting from the plowing of wheat stubble in which hens were nesting. Regional Variations in Sex Ratios Sex ratios in ducks were found to vary with migration routes and wintering grounds, fig. 8. The relative number of drakes among mallards reported bagged in the late per cent hens) than drakes among 13,959 mallards trapped and banded in a period of about 12 years. More hens than drakes were reported among a few mallards in hunters' bags in eastern Wisconsin by Hopkins (1947:28), who also reported more hens than drakes among mallards that were trapped and banded in the area. The report by Hopkins is interpreted to 80 I- 70 60 50 40 30 20 jz-;-^ Adult Class Juvenile Class MANITOBA OHIO WISCONSIN ILLINOIS ARKANSAS NEBRASKA UTAH Fig. 8.—Drake percentage in juvenile and in adult mallards checked in hunters' bags in each of six states and the province of Manitoba, 1946-1948. More drakes than hens were checked in each state or province except Wisconsin. 1940's in Ohio was considerably more than the relative number among mallards reported bagged in Nebraska, fig. 8 ; the two areas are in approximately the same latitude but in different flyways. In each area more drakes than hens were bagged. The much greater kills among juvenile j drakes than among adult drakes is unex- I plained. I A preponderance of hens was reported I for an area in British Columbia by Munro i (1943:247), who found more hens (54.3 mean that more hens than drakes of the mallard were in the area during the fall of 1946, the period covered by the report. Drakes and hens apparently occur in various ratios in various areas of their wintering grounds. In Louisiana, table 19, inspection of hunters' bags showed that not only was the relative number of drakes low for all species but that hunt- ers killed more hens than drakes in the mallard, pintail, green-winged teal, and lesser scaup. To the west, on the coast of 420 Illinois Natural History StRvtv BuLLtTix Vol. 27, Art. Texas, hunters bagged more hens than drakes in the mallard, gadwall, shoveler, redhead, and canvasback. On the Texas coast, the relative number of drakes was unusually high only in the pintail and lesser scaup, species in which a large part of the population winters in Mexico. In every duck species for which com- parable figures were collected, the drake segment was larger in Tennessee, an area representing the northern part of the win- tering grounds in the Mississippi Flyway, than in Louisiana, at the southern ex- tremity of the flyway, table 19. Sex ra- tios obtained for the mallard, baldpate, and green-winged teal from inspection of ducks found dead in the Texas Panhan- dle, table 31, favored drakes to a greater extent than did sex ratios for these same species obtained from inspection of hunt- ers' bags on the Texas coast, table 19. Drakes predominated in pintails about equally in these two Texas areas. In Texas coast mallards cited by Singleton (1953:57), the sex ratio for adults was almost evenly balanced ; however, among juveniles, there were substantially more hens than drakes. Relatively greater num- bers of hens than of drakes may occur in waterfowl populations to the south, in Mexico. Although drakes greatly predominated among lesser scaups taken on the Texas coast, table 19, hens predominated among redheads and canvasbacks. Because only small numbers of redheads and canvas- backs are known to winter north of the Texas coast in the Central Fl}^vay and because of the known preponderance of drakes in these species, it is assumed that large numbers of drakes of these species winter farther south on the Gulf Coast, in Mexico. In the Currituck Sound area of North Carolina, where many species of ducks winter, bag checks in 1948-1952 showed the number of drakes to be relatively low for the green-winged teal, shoveler, can- vasback, lesser scaup, and ruddy duck (Oxyura jarnaicensis) , table 19. Because large numbers of these ducks winter to the north of Currituck Sound, it is be- lieved that the drakes of these species may be more numerous in those areas. The relatively large numbers of drakes among bagged pintails and gadwalls at Curri- tuck Sound suggest that populations of these species to the south have proportion- ally fewer drakes. During the spring migration, the re- gional variations in the sex ratios of ducks are even more pronounced than they are during the fall migration. Table 24 shows the variations in sex ratios among several species of ducks in 10 regions of North America. The mallard and the blue- winged teal showed less regional variation in sex ratios than the other species. In no region did the drake percentage for the mallard deviate more than 3.3 percentage points from the average for all regions represented. The comparable figure for the blue-winged teal was 5.3. Drakes formed more than 60 per cent of the pop- ulation of eight species in Illinois, six in Iowa, and three each in California, North Dakota, and Indiana, table 24. Illinois appears to be on a major flj'way route for male ducks during the spring. In most species migrating through Illi- nois, the number of drakes in the spring, table 24, is relatively larger than the num- ber of drakes in the fall, table 14. There is evidence that adult drakes of certain species, especially the divers, make longer flights during the fall migration than do the hens and the juveniles of both sexes. The probability that, in the fall, adult drakes of these species pass over Illinois, or move more quickly through the state than do the hens and juveniles, suggests one explanation for the pronounced dif- ferences between fall and spring sex ratios. Sex ratios of ducks show less deviation from balanced sex ratios in northern areas than in other areas of the Mississippi Flyway in spring, table 24. In Minne- sota, North Dakota, and Manitoba, sex ratio data were collected primarily on ex- tensive lakes and marshes frequented by large numbers of transient ducks. Be- cause of the location of the area, the size of the samples, and the period of years over which data were collected, the sex ratios from North Dakota appear to rep- resent the various species in spring better than the sex ratios from other areas. Mortality Factors Affecting Sex Ratios As an approach to an evaluation of fac- tors that contribute to deviations from August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 421 Table 28.—Drake percentage in each of 10 species of ducks banded by Ducks Unlimited* in the prairie provinces of Canada, 1939—1950, and the drake percentage in the year-of-banding recoveries. The difference between these two percentages for each species is a measure of hunter selectivity for that species, -\- for drakes, — for hens.* 422 Illinois Natural History Survkv Bullktin Vol. 27. Art. b 2s? is 1Z ^ Q August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 423 the south end of San Francisco Bay northward through the delta and into the lower Sacramento Valley (Rosen & Bischoff 1950:147-8). Although Petrides & Bryant (1951: 203) found some indication that the smaller the duck the more susceptible it is to fowl cholera, the weight difference between drakes and hens in any one spe- cies is not great enough to account for a material difference in mortality rates. A small number of drake-hen ratios for mal- lards and pintails, living birds and victims of fowl cholera, in the Texas Panhandle in 1944-1946, table 30, suggest that the disease is not markedly selective of either sex. Sex ratios for several hundred ducks presumably dying from fowl cholera in the Texas Panhandle in 1944-1946 and 1948 are given in tables 30 and 31. The loss of pintail drakes was proportionally greater in 1948 than in 1944-1946. The loss of mallard drakes showed approxi- mately equal percentages in the two pe- riods. In each period, the loss was pro- portionally greater among pintail drakes than among mallard drakes. Available evidence suggests that fowl cholera is not an important cause of dif- ferences in mortality rates between the sexes. In the recorded outbreaks of this disease among ducks, drakes have predom- inated in the populations and have suf- fered losses proportionally no greater than those of hens. Lead Poisoning.—Among migratory waterfowl, lead poisoning is more wide- spread geographically than either botulism or fowl cholera. It has been estimated (Bellrose 1959:282) that among all spe- cies of waterfowl in North America 2 to 3 per cent die from this disease each year. Following experiments with penned wild mallards, Jordan & Bellrose (1951 : 21) concluded that: The hen mortality from lead poisoning was found to be double the drake mortality, except Table 30.—Drake percentages among pintails and mallards in the Panhandle of Texas, 1944—1946, as determined by (1) counts of ducks believed to be victims of fowl cholera and (2) visual observations of healthy ducks.* 424 Illinois Natural History Survey Hulletin Vol. 27, Art. 6 Table 32.—Drake percentages among mallards picked up dead or incapacitated from lead poisoning in several areas of the Mississippi Flyway during late fall and winter, 1939—1955. Place Year Sand Lake, South Dakota. . . Heron Lake, Minnesota Lake Chautauqua, Illinois. . . Batchtown, Illinois Chariton County, Missouri. . Ciaypool Reservoir, .Arkansas Catahoula Lake, Louisiana . . 1951 1939 1941-1955 1953 1949 1954 1953 Number Checked 59 194 753 47 53 100 243 Per Cent Drakes 57.6 63.4 62.8 68.1 64.2 73.0 44.4 in the spring season when hens entered the breeding phase. At this season the food in- take of penned wild hens increased steadily until it equaled, then exceeded, that of penned wild drakes. During this period hens proved to be less susceptible to lead poisoning than were drakes. At all other seasons hens ate less food than did drakes. In field experiments with mallards, some of which had been dosed with lead shot and some of which had not been dosed, Bellrose (1959:276) found that: Because of the smaller number of experi- ments conducted with hens than with drakes, it is more difficult to appraise mortality from lead poisoning in the hens. However, the available data suggest that, among hens and drakes with identical ingested shot levels, hens probably suffer twice as great a mortality as drakes in the fall and a small fraction of the mortality of drakes in late winter and spring. Actual counts of mallards picked up dead or incapacitated from lead poisoning in the Mississippi Flyway during late fall and early winter show a large pre- ponderance of drakes, table 32. Field observations on healthy ducks in the re- gion also show a preponderance of drakes in the wintering populations. Because most outbreaks of lead poisoning that have been reported are from the northern periphery of the wintering grounds and because drakes greatly predominate in wintering populations in those areas, un- doubtedly an appreciably greater number of drakes than of hens have died from this disease. Predators and Sex Ratios.—Inves- tigations of predation on waterfowl are not adequate to provide a substantial basis for appraising the role of predation in se- lective mortality for drakes or hens. The hens, while incubating eggs for 3 or 4 weeks, and later, in caring for the flight- less young for 6 to 10 weeks, may be ex- posed to greater predation than drakes. During the molt or flightless period, when the tendency of hens is to remain on small bodies of water, while drakes congregate on large lakes or marshes, the hens may be subjected to greater predation than drakes. Aloreover, the poor physical con- dition resulting from the stress of egg laying and molting may also cause the hens to be more vulnerable to predation. Kalmbach (1937:383-4), in summa- rizing the fate of 512 duck nests on the prairie breeding grounds in Canada, re- ported that eight egg-laying or incubating hens were known to have been killed by predators. Other hens may have been killed by predators without leaving evi- dence; 40 nests had been deserted, and 53 had been destroyed by unknown agents. In a study that included 340 "active" duck nests in southeastern Saskatchewan during 1953, Stoudt & Duller (1954: 58-9) found seven nesting hens that had been killed by predators. During three seasons on a 1.5 square mile study area near Minnedosa, Manitoba, Alex Dzubin of the Canadian Wildlife Service (letter, March 26, 1955) found 13 hens and 6 drakes killed by predators, mowers, or muskrat traps. Because his study area was atj'pical in being flanked by paved highways along two boundaries, as well as by telephone and electric power wires, ducks killed by colliding with cars or by flying into wires were not included in his figures. During a study of the fate of nests on farm land near Delta Marsh on the Por- tage Plains of Manitoba, 608 nests of seven species of ducks were examined (Milonski 1958:223, 225); although many nests were believ-ed to have been lost to predation (striped skunks de- August, 1961 Bellrose el al.: Sex Ratios and Age Ratios 425 stroyed 7 per cent of the pintail nests and 51 per cent of the mallard nests) only five hens were known to have been killed by predators. On Illinois study areas, raccoons de- stroyed 304 out of 1,579 wood duck nests and killed 103 hens in a period of 7 years. Minks killed other nesting wood duck hens, and even fox squirrels were respon- sible for the death of several hens. Census records indicate that during the nesting period wood duck drakes suffered negligi- ble losses. Agricultural Operations and Sex Ratios.—Losses resulting from mowing or combining operations on farm land are selective for nesting hens. Such losses would affect only species nesting in crops subject to mowing or combining. It seems probable that the mallard, pintail, gadwall, green-winged teal, blue-winged teal, bald- pate, and shoveler would be most exten- sively concerned. The potential loss of nesting hens is great, because extensive areas of farm land are included in the breeding grounds. As long ago as 1948, Lynch (1948:28) pointed out that the 75,000 square miles comprising southern Saskatchewan is far from being a vast undisturbed prairie and that "three-fourths of this 'Duck-Factory' are grain-fields. The remainder is heavily grazed." According to Forrest Lee of the Min- nesota Department of Conservation (let- ter, January 9, 1955), the loss of blue- winged teal hens from mowing may be appreciable in Minnesota. One farmer near Hutchinson, despite the use of a flushing bar, in 1 year destroyed three hens while he was mowing an alfalfa field. A normally productive pond on his farm had no broods in that year. Interviews with a large number of farmers in the area indicated that such losses were not unusual. Of 122 mallard and blue-winged teal nesting hens for which there was a chance of being killed (on nests destroyed directly or indirectly) in the mowing of 592 acres of hay on Horicon National Wildlife Refuge, Mayville, Wisconsin, only 5 were killed (Labisky 1957:195-7). It was believed that this low vulnerability of nesting hens resulted because "dabbling ducks generally rise swiftly and nearly vertically from the nest when flushed by the mowing machine, thus avoiding the cutting bar." While making observations on 608 nests of seven species of ducks on farm land near the Delta Marsh in Manitoba, Mil- onski (1958:223) found only two hens killed in mowing operations. The available data indicate that losses of nesting hens resulting directly from agricultural operations do not contribute importantly to imbalance in adult sex ratios. Stress and Sex Ratios.—Little is known about stress, as defined by Selye (1956:3), in its relation to mortality in ducks. Kabat et al. (1956:44) found that in pheasants {Phasianus colchicus) the "seasonal variation in resistance to the applied stress and survival time was re- lated to the physiological condition of the hen at particular times of the year." In July and August, pheasant hens that had completed or were about to complete their egg laying and were molting flight feath- ers were in their poorest physical condi- tion of the year. Survival of pheasant hens under applied stress was shortest in June, July, and August and longest in April, immediately prior to egg laying (Kabat et al. 1956:12). The average survival period in July was 13 days in one year and 18 days in another, compared to 21 days in October, 27 days in Decem- ber, 29 days in January, 34 days in Feb- ruary, 40 days in April, 22 daj^s in May, 17 days in June, and 13 days in August. Without doubt the greatest energy drain experienced by duck hens in the en- tire year occurs during late spring and summer as a result of egg laying, in- cubation, brooding of young, and post- nuptial molt. This sequence of activity probably places the hens in much greater jeopardy to stress than the drakes, which experience marked depletion of energy only through the period of the post-nuptial molt. Harold C. Hanson of the Illinois Nat- ural History Survey has determined (manuscript in preparation) that among Canada geese {Branta canadensis) the stress of the molt is especially severe on the female following the energy demands of egg laying and caring for the young and that this produces a differential effect on the sexes which may be the primary cause 426 Ii.Lixois Natural History Survey Bulletin Vol. 27, Art. 6 for the preponderance of males in adult populations. Evaluation of Mortality Factors.— Information available on the principal mortality factors affecting sex ratios in the North American duck population indi- cates that hunters and disease take rela- tively more drakes than hens and that predators may take relatively more hens than drakes. From the time of hatching to the be- ginning of the breeding season, only slight the imbalance between the sexes in this population. Influencing the age composition, and therefore to a large extent the sex ratios of the population, are ( 1 ) productivity and (2) mortality. The more productive a species of water- fowl, the greater is apt to be the propor- tion of juveniles in its population at the opening of the hunting season. The greater the proportion of juveniles in a population, the more nearly balanced is Table 33.—Shooting losses, as measured by per cent of banded ducks recovered in year of banding, and drake percentage in the population of each of seven species of ducks. Species Dabbling Ducks Mallard Baldpate .... Pintail Shoveler Diving ducks Redhead . . Canvasback. Lesser scaup. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 427 rate for juveniles has been about 50 per cent, whereas the kill rate for adults has been 20 or 30 per cent; the annual mor- tality rates have been about 70 per cent for juveniles and about 55 per cent for adults. Of the canvasback, Geis (1959: 254-5) reported that the year-of-banding recovery rates (per cent of birds banded that were shot by hunters and had bands recovered within a year of the time of banding) were 22 per cent for juveniles and 14 per cent for adults; the annual rates for mortality from all causes were 77 per cent for juveniles and 35 to 50 per cent for adults. Mallard drakes banded as juveniles in Illinois had a first-year mortality rate of about 55 per cent; mal- lard drakes banded as adults had a first- year mortality rate of 36 per cent and an average mortality rate of about 40 per cent (Bellrose k Chase 1950:8-9). The high mortality rate in the juvenile class of redheads and canvasbacks has re- sulted in relatively large numbers of old birds in the breeding populations of these species and consequently a large prepon- derance of drakes, table 33. Extremely large drake segments noted in lesser scaup populations are evidently not related to high juvenile mortality re- sulting from hunting. The vulnerability rate of juveniles in this species, table 45, is insufficient to account for the large im- balance between the sexes, table 33. The causes of the imbalance seem to be ( 1 ) low shooting pressure on the species, ta- ble 45, (2) a low reproductive rate, table 62, and consequently (3) a relatively small number of juveniles in the popula- tion, table 53. Variations in the age composition of waterfowl populations are largely respon- sible for variations in sex ratios among species of ducks. Sex ratios of various species of ducks in the spring in North Dakota, table 24, indicate that the mal- lard has relatively the largest number of yearlings in its breeding populations; this species is followed in order by the pintail, shoveler, redhead, blue-winged teal, ring- necked duck, baldpate, canvasback, lesser scaup, and ruddy duck. The Question of Surplus Drakes It seems reasonable to question the value of those drakes in excess of the number needed to provide mates for the hens in waterfowl populations. In the event such drakes do not play an essen- tial role in species survival, an effort should be made to provide for their utili- zation. While drakes outnumber hens in all species studied, drakes occur in relatively greater numbers among the diving ducks than among dabblers, table 24. Exam- ination of available knowledge on the re- productive biology characterizing these two subfamilies reveals nothing which suggests that extra drakes may be more essential to the maintenance of popula- tions of diving ducks than of dabblers. The hens of diving ducks engage in less renesting activity than do the hens of dabbling ducks, and some observers feel that diving duck drakes tend to be more persistent in remaining with nesting hens than do the drakes of dabbling ducks. Spe- cies differences in this respect were ob- served among dabbling ducks by Sowls (1955:101), who wrote that while late-season or renesting courtship flights of mallards, gadwalls and pintails were common, we seldom saw them in the shovellers and blue-winged teal. I suspect that the difference occurred because of the length of time the drakes stayed with their hens after the clutches were laid. Blue-winged teal and shoveller drakes did not abandon their hens until incu- bation was well advanced ; while mallard, pin- tail and gadwall drakes abandoned their hens shortly after the clutches were completed. Robert I. Smith of the Illinois Natural History Survey (personal communica- tion, December 9, 1960) also observed that blue-winged teal and shoveler drakes tend to remain with their hens longer than do the drakes of mallards, pintails, and gadwalls; in exceptional cases, mallard, pintail, and gadwall drakes may remain with their hens throughout and even be- yond the incubation period. On the breed- ing grounds, drakes outnumber hens to a greater extent among pintails, blue-winged teals, and shovelers than among mallards and gadwalls, table 34. A pattern of sorts seems apparent here, but it does not afiford obvious support of a need for extra drakes in reproduction. The superficially excessive number of drakes may be significant to population dynamics among waterfowl in ways which are not directly related to the in- surance of successful reproduction. At 428 Illinois Natural History Survhy Bulletin Vol. 27, Art. 6 times, harassment of nesting hens by idle drakes may result in an important amount of nest desertion and possibl\ a reduction in productivity. Along with the severe stress of reproductive activity, harassment by drakes may contribute indirectly to mortality among hens. It is conceivable, too, that, if extra drakes are truly sur- plus, they may also create undesirable stress by occupying space and consuming food essential to the welfare of the pro- ductive segment of the population. Perhaps insight into the value of extra drakes could be obtained through an ex- perimental procedure designed to reduce the number of drakes in a subpopulation of a species having a large drake segment. Re- duction of drake numbers could possibly be accomplished by deliberate hunting of drakes in places and at times when they were concentrated apart from the hens or when they could be decoyed from the hens and brought within shooting range. Tep- lov & Kartashev (1958:159, 161), re- porting on observations made on the Oka State Sanctuary and on adjacent shooting areas in Russia, indicated that hunters are "permitted in spring to obtain the drakes of all species and also geese on passage. The most general method of ob- taining waterfowl in spring is the shoot- ing of Mallard drakes which go to a de- coy duck." In Russia, the killing of fe- male ducks is forbidden in spring. Such an experiment as that outlined above would meet the added objective of deter- mining whether regulated hunting might be directed at what is possibly a truly ex- pendable part of the waterfowl popula- tion. Sex Ratios as Measures of Production Because sex ratios reflect the age com- position of a duck population, analysis of year-to-year differences in the sex ratios of a species offers a method of diagnosing the yearly changes in production. Also, be- cause sex ratios for each species of water- fowl vary from season to season within any year, as a result of hunting and nat- ural phenomena, the sex ratios obtained during a particular season (fall, winter, spring, or summer) should be compared with the sex ratios obtained during only corresponding seasons of other years. A August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 429 75 50 25 Hens Juveniles Hens Juveniles 1939 194! 1943 1945 1947 1949 1951 1953 1955 1959 Fig. 9.—Year-to-year changes in the hen percentage and in the juvenile percentage in mal- lards checked in hunters' bags in the Illinois River valley, 1939-1955 and 1959. Percentages have been adjusted so that the means for juveniles and hens are equal. comparison of the sex ratios in the sum- mer of one year with the sex ratios in the winter of the same or another year would be biased by the disproportionate hunting losses of juveniles, which have approxi- mately balanced sex ratios. As a means of measuring yearly pro- duction, sex ratios have certain basic ad- vantages over age ratios. For many spe- cies of ducks, such as the divers, age ratio data, derived from bag checks during the autumn, are difficult to obtain in ade- quate numbers. For the most important species, it is much easier to obtain large samples of sex ratio data from field ob- servations than to obtain large samples of age ratio data from bag inspections. Less skill is required to determine the sex of a duck in nuptial plumage than the age of a duck in any plumage. To test the validity of sex ratios as cri- teria of duck production, we have made a comparison, fig. 9, of sex ratios with age ratios, which are direct reflections of pro- duction. Both ratios were obtained from mallards killed by Illinois hunters in 1939- 1955 and 1959. We have also made, for several species of ducks, comparisons of sex ratios derived from observations on the breeding grounds, table 34, with the number of juveniles per hen killed in Illinois, table 62. As shown in fig. 9, the sex ratios (per cent hens) and the age ratios (per cent juveniles) obtained from mallards killed by Illinois hunters differed markedly in several years. The fluctuations in age ra- tios tended to be of greater magnitude than those in sex ratios ; the peaks were higher in age ratios than in sex ratios, and the troughs were deeper. An over-all correlation of +0.59 suggests that only fair agreement exists between the sex ra- tios and the age ratios. We conclude that sex ratios derived from bag inspections provide a fair index to productivity but not so good an index as age ratios. Sex ratios obtained on the breeding grounds, table 34, do not appear to pro- vide a more reliable index to production than sex ratios calculated from bag in- spections in Illinois. Data for the breed- ing seasons of 1935-1942 and 1947-1950 (except certain data from Furniss, table 34) show that the drake percentages for the mallard, gadwall, pintail, green- winged teal, and ring-necked duck did not, in any season for which figures are available, deviate from the average for the species by as much as 5 per cent. This lack of deviation indicated relatively sta- ble populations; data in table 62, showing the number of juveniles per adult hen for the years 1946-1949, indicated increasing 430 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 populations for all of the above-men- tioned species except the gadwall. AGE RATIOS Two commonly used indicators of waterfowl production are brood densities (the number of broods per unit of area on the breeding grounds) and age ratios (the mathematical relationship between adults and juveniles old enough to fly). Brood density surveys supply informa- tion of value for making preseason ad- justments in hunting regulations. How- ever, data on brood densities are not be- lieved to constitute precise indices of pro- duction. Substantial proportions of the broods present in an area are missed by observers employing survey techniques us- ually considered practicable (Anderson 1953:8-10). Correction for unobserved broods may never yield to reliable stand- ardization, for the percentage of broods not found by observers varies with many factors such as time of day, time of season, habitat, area, and waterfowl population densities. Age ratios are believed to afford a more promising basis than brood counts for measuring waterfowl production, although they, like data on brood densities, are seldom true indices of production. This section of the paper is written with the intention of opening the way to a more effective use of age ratios in wa- terfowl management. The following as- pects of age ratios and their use are con- sidered : age criteria, sampling methods for obtaining age ratios, seasonal and re- gional variations in age ratios, factors tending to bias age ratios, age ratios as measures of production, environment in relation to production, production in dif- ferent species, and the place of age ratios in population management. Age Criteria In 1938, when biologists of the Delta Waterfowl Research Station at Delta, Manitoba, and of the Illinois Natural His- tory Survey at Havana, Illinois, initiated waterfowl research programs involving the inspection of large numbers of ducks bagged by hunters, the need for finding consistently reliable external characteris- tics by which to separate juveniles from adults was recognized. The best external indication of age known at that time had been pointed out by Pirnie (1935:275). It was based on the appearance of the tips of tail feathers, those of adults being rounded or pointed, those of juveniles be- ing blunt or notched. However, in the mallard, an important species in Illinois and at Delta, young birds were known to replace their juvenile feathers with adult feathers early in the fall ; hence, they could not be accurately aged by this char- acteristic throughout the hunting season. In some species, notably those in the genus Aythya, the tail feather criterion was found to be more persistent than in the mallard, but, even so, it was not reliable throughout the hunting season. During the fall of 1938, biologists at the Delta and Illinois stations searched for some characteristic by which to sep- arate juveniles from adults in the mallard and other early-molting species. The search at Delta was concentrated on plum- age, while that in Illinois was concerned with a character, pointed out by Tice- hurst (1938:772-3) as being related to immaturity: striae "at the tip of the nail of both upper and lower mandibles." The Illinois group also investigated various parts of the skeleton that might exhibit differences in ossification between juve- niles and adults. At that time, neither group was successful in the search for a characteristic by which to separate ducks into the two age classes. In the following winter, Gower (1939: 427) called attention to the bursa of Fa- bricius as a criterion of age in ducks. A short time later Hochbaum (1942:301), aided by the findings of Gower and the work of Owen (1866:244-5), learned that juvenile drakes of 5 to 10 months of age could be separated from adult drakes by the size of the penis, fig. 1. This find- ing, put to use in the summer and fall of 1939, provided a method of differentiat- ing between juveniles and adults of both live and dead drakes. The new method proved faster and easier to use than the bursal method. Also, it provided for ac- curate separation of drakes from hens in all stages of plumage. However, the bursa was found to persist for several weeks after the transition from juvenile- to adult-type penis and therefore provided a August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 431 basis for separating juveniles from adults over a longer period of time than that af- forded by the penis. Hochbaum (1942:303-4) pointed out that the oviduct, which opens into the cloaca in adult females, is sealed by a membrane in immature females, fig. 1. Wildlife technicians in Illinois have found collected from duck hunters and shipped to a central point for interpretation by trained personnel. Sampling for Age Ratios Data on the age ratios of ducks may be obtained by examination of birds trapped for banding, shot by hunters, or killed by 80- 70 - z ^ 60 50 40 30 20 McGinnis Slough —s I y \ inois Valley 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 Fig. 10.—Year-to-year changes in the juvenile percentage in mallard drakes trapped at Mc- Ginnis Slough and at Lake Chautauqua and in mallards checked in hunters' bags in the Illinois River valley, 1939-1957. that, until at least mid-January, the pres- ence of a closed oviduct and a bursa un- failingly indicates a juvenile hen. Occa- sionally, a hen is found that shows an open oviduct and a small bursa; such a bird is considered adult. Most wildlife technicians have restricted their aging of hens to individuals that have been bagged by hunters. However, Hanson (1949) developed a technique that can be used for aging live females in both ducks and geese. In 1958, after completion of most of the field work for the studv reported here. Carney & Geis (1960:376-9) found that, in certain species of ducks, juveniles and adults could be identified with a high de- gree of accuracy on the basis of differ- ences in the wing plumage. The technique described by these authors makes possible the extensive sampling of a^e ratios of ducks in all four flywavs of North Amer- ica. Large numbers of wings could be disease. It seems desirable that the rela- tive merits of these sources of data be ap- praised. In the present study, all three sources of data were used for obtaining age ratios. Examination of Trapped Ducks.— A comparison of the age ratios of mallard drakes trapped at Lake Chautauqua, table 35, and the age ratios of mallard drakes and hens taken by hunters in the Illinois River valley, table 36, discloses marked disparity in the number of juveniles per adult between the trapped ducks and the harvested ducks. The data show rela- tively fewer juveniles among the drakes trapped at Lake Chautauqua than among the ducks taken by hunters in the Illinois River valley, tables 35 and 36 and fig. 10. However, among drake mallards captured at McGinnis Slough in traps similar to those used at Lake Chautauqua, a higher proportion consisted of juveniles, table 37 and fig. 10, than among mallard drakes 432 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 trapped at Lake Chautauqua or mallards bagged in the vicinity of that lake. Despite marked differences in the size of samples between trapped and shot mal- lards, the two sampling procedures indi- cated similar ^Tar-to-year trends in age ra- tios, fig. 10. The statistical correlation in the annual changes in age ratios between mallard drakes trapped at Lake Chau- tauqua and mallards shot along the Illi- nois River was found to be significant (r=+0.96, 13 d.f.) at the 99 per cent level. Mallards inspected in hunters' bags in the Illinois River valley (1939-1949) and mallard drakes taken in traps at Lake Chautauqua (1939-1944 and 1947) showed similar trends in age ratios for most of the hunting season, fig. 11. The trends tended to be parallel except in early December. The correlation between age ratios calculated weekly for the samples 70r- Trap Catches -0.15 2nd 3rd OCTOBER 2nd 3rd NOVEMBER 1st 2nd 3rd DECEMBER Fig. 11.—Week-to-week changes in the adult percentage of the autumn flight of mallards in Illinois, as indicated by two sampling methods: checks of mallards in hunters' bags and inspec- tion of mallard drakes caught in banding traps. Bag data are for the Illinois River valley, 1939- 1949; trap data are for Lake Chautauqua, 1939-1944 and 1947. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 433 of trapped and shot mallards was signifi- cant (r=+0.94, 7 d.f.) at the 99 per cent level. Behavior may well account for the large juvenile proportion in the mallard drakes taken in traps at McGinnis Slough, fig. 10, and the small proportion in those taken in traps at Lake Chautauqua. As discussed under sex ratios, mallard drakes were ob- served to be more aggressive than hens in pushing their way into the traps at Lake Chautauqua. Perhaps adults shouldered young birds aside in aggressive efforts to get at the bait. Lake Chautauqua had a much greater density of mallards and com- paratively less natural food than McGin- Table 35.—Number of juveniles per adult among mallard drakes trapped and banded at the Chautauqua National Wildlife Refuge, near Havana, Illinois, 1939-1944 and 1947-1959. Year 434 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 37.—Number of juveniles per adult among mallard drakes trapped and banded at McGinnis Slough, Cook County, Illinois, 1940—1947. Year August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 435 Table 39.—Comparative vulnerability (to hunting) of adult and juvenile mallard drakes banded at the Chautauqua National Wildlife Refuge, near Havana, Illinois, 1939-1944 and 1947—1952; vulnerability measured by year-of-banding recoveries. Ducks banded with reward bands (Be.lrose 1955) in 1949, 1950, and 1951 were not included in this table. Year 436 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 40.—Comparative vulnerability (to hunting) of adult and juvenile mallard drakes banded at McGinnis Slough, Cook County, Illinois, 1942—1947; vulnerability measured by year- of-banding recoveries. Year August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 437 McGinnis Slough; also, several other ref- drakes became less vulnerable, table 44, uges occur within the 25- to 30-mile feed- presumably as a result of increased experi- ing radius of mallards congregating at ence with hunters. During the early part Chautauqua, whereas none occurs within of the season, the juveniles were bagged that distance of McGinnis Slough. It about four times as readily as adults; late seems evident that adult mallards and in the season they were bagged only about Table 43.—Comparative vulnerability (to hunting) of adult and juvenile blue-winged teal drakes and hens banded in Illinois at McGinnis Slough, Cook County, 1942—1947, and at Moscow Bay, Mason County, 1949—1951 ; vulnerability measured by year-of-banding recoveries. Year 438 Illinois N.aturai. History Survey Bulletin Vol. 27, Art. 6 43, it is suspected that some unusual local conditions affected the Canadian bandinjrs of these three species. Perhaps many juvenile teals and shovelers lost hands, for, until 1957, the banding office at the Patuxent Research Center, Laurel, Table 44.—Seasonal change in comparative vulnerability (to hunting) of adult and juvenile mallard drakes banded at the Chautauqua National Wildlife Refuge, near Havana, Illinois, in 1940, 1942, 1943, and 1952. Week August, 1961 Bellrose et al: Sex Ratios .and Age Ratios 439 Maryland, recommended size 6 for the shoveler, although a size 5 is large enough for that species. Many banders used size 5 to mark green-winged teals, although size 4 is the proper size. Perhaps natural mortality was unusually severe in the young teals and shovelers between the time of banding and the opening of the hunting season ; very few bands are recov- ered from ducks that are not bagged by hunters. Still another possible explana- tion for unexpectedly low relative vulner- ability rates for juveniles on the Canadian breeding grounds has been posed by Rob- ert I. Smith of the Illinois Natural His- tory Survey. Smith has observed on the breeding grounds that fall flocking be- havior of juveniles differs from that of adults. Prior to migration, juveniles tend to congregate, while many adults remain as single hens of male-female pairs. The nature and time of this flocking behavior. Smith believes, varies with species and with the success and duration of the nest- ing season. Flock size is probably inverse- ly correlated with vulnerability, thus tend- ing to give greater protection to the con- gregated juveniles than to tlie single adult hens or paired adults. Band recovery data showed pronounced differences among species in the vulner- ability rates of juveniles banded in Can- ada, table 45. Among species other than the teals and the shoveler, juveniles were least vulnerable to the gun in the mallard and most vulnerable in the redhead. Other data obtained from bandings at national wildlife refuges also disclosed wide varia- tions in juvenile vulnerability; they showed the mallard with a comparatively low juvenile vulnerability rate, followed by the pintail, and showed the redhead with the highest vulnerability rate. Thus, the gun vulnerability of juve- niles compared to that of adults was found to vary by place, time of hunting season, year, and species. Gun vulnerability figures for correct- ing age ratios obtained by checking hunt- ers' bags in one or more flyways can best be obtained by banding adults and juve- niles in southern Canada just prior to the opening of the hunting season. When adequate data from banded ducks are available, they provide a means of testing for and, if necessary, correcting for the relatively greater vulnerability of juveniles. We believe that age ratios of ducks obtained from bag samples and cor- rected for the greater vulnerability of juveniles of¥er the best means of deter- mining the adult-juvenile composition of duck populations. However, before these data are used to evaluate production, an appraisal of the influence of season and geography on age ratio samples is needed. Examination of Disease Victims. —At times, age ratios have been obtained from large samples of ducks which have been victims of disease. During fowl Table 46.—Juvenile percentages among botulism victims in five species of ducks at the Bear River Migratory Bird Refuge, Utah, during late summer, 1952.* 440 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 cholera epizootics in wild ducks, records have been made of the species and se.x af- fected, but little attention has been given to the ages of victims. In Utah, large numbers of waterfowl that were victims of botulism at the Ogden Bay Bird Ref- uge were classified as juveniles or adults by Noland F. Nelson, tables 21 and 22, and ducks lost to botulism at the Bear River Migratory Bird Refuge were sim- ilarly classified by Jack P. Allen, table 46. The degree to which botulism toxin is se- lective for the two age groups has not been investigated. Epizootics resulting in extensive loss of waterfowl cannot be relied upon as de- pendable sources of data on age ratios be- cause of irregular occurrence and site lim- itations. However, advantage should be taken of such occasions for the purpose of obtaining supplementary age data and for investigating the extent to which disease may be selective for age classes. Seasonal Variations in Age Ratios Because adults and juveniles, like drakes and hens, have different migration sched- ules, age ratios calculated for any given area have seasonal variations. Differential migratory movements of adult and juvenile age groups often orig- inate on the breeding grounds, where most of the adult drakes of most species leave their mates early in the nesting period to congregate on large lakes and marshes ; these areas may be in the immediate breed- ing area or up to hundreds of miles dis- tant. After the broods become independ- ent, the hens leave them and molt their flight feathers but usually remain in the area where they nested (Hochbaum 1944: 119, 122). Hens that have been unsuc- cessful in their nesting efforts may join the drakes on the lakes or marshes, where they molt. Certain large lakes and marshes on the breeding grounds serve ducks as gathering areas preceding southward migration. One of these areas is the Delta Marsh at the south end of Lake Manitoba, Canada. The number of juveniles per adult among mallards in hunters' bags on that marsh was checked for several weeks in 1946 and 1947, tables 47 and 48. There was a re- duction in the number of juveniles per adult from the third week to the fourth week in September, 1946, followed by a gradual increase in the number of juve- niles per adult until the first week in No- vember, when a very sharp decrease took place. There was a marked decrease in the number of juveniles per adult in the pe- riod October 20-25, 1947. When the Table 47.—Number of juveniles per adult among mallards checked in hunters' bags on the Delta Marsh, Manitoba, in each of 6 weeks in the autumn of 1946. August, 1961 Bellrose et ah: Sex Ratios and Age Ratios 441 100 90 =• ::;i:i;x;;;x;x::;i;x;x;;;:;DECE M BER i -i-. 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 Fig. 12.—Year-to-year variations in the seasonal migration of juvenile mallards through the Illinois River valley, 1939-1950, as shown by the proportion of each year's juvenile flight that was in the valley in each of 6 weeks in autumn. 60) and in 1953 (Lynch & Gollop 1954: 47; Gollop 1954:67; Hawkins 1954:77). That the age composition of the mal- lard population in Illinois varied from week to week in the fall is shown by checks of hunters' bags, table 44. In any one year, pronounced week-to-week vari- ations in the age composition of mallards taken by hunters in Illinois suggest that there may be many migratory movements, some scarcely detectable, within a local population. The adult-juvenile composition of the mallard flight in Illinois for the period 1939-1949 is reflected in fig. 13. Gen- erally, juveniles made up a greater part of the mallard bag early in the season than later. The juvenile proportion in hunters' bags soon declined, as indicated by data collected during the first half of Novem- ber; it recovered somewhat during the second half of November but declined again during the first 2 weeks of Decem- ber. The decline in December resulted as juveniles moved farther south and large numbers of adults moved into Illinois from the north. In 6 of 7 years, juvenile mallards in Arkansas formed a greater proportion of the hunters' bags in the second than in the first of two periods during which data were collected, table 49. The findings shown in fig. 13 and tables 49 and 50 suggest that, between the mid-flyway areas (Illinois) and the wintering grounds (Arkansas), juveniles may be more prone to leisurely migration than adults. The daily change in age composition of the mallard bag at Stuttgart, Arkansas, for December 2-11, 1950, is given in ta- ble 50. A marked change in the relative number of juveniles in the bag occurred on December 8. A large southward flight of mallards from Illinois on December 7, as a result of zero weather and snow, con- tained a relatively large number of juve- 15-31 OCTOBER 1-15 16-30 NOVEMBER 1-15 DECEMBER Fig. 13.—Juvenile-adult composition of the autumn flight of mallards in Illinois, as indi- cated by checks of hunters' bags in the autumns of 1939-1949. 442 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 49.—Number of juveniles per adult among mallards checked in hunters' bags at Stuttgart, Arkansas, in 12 hunting seasons. Hunting Season August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 443 ratios of ducks in a Utah area before the hunting season. These data, unlike the data from ducks trapped at Ogden Bay, do not show a large juvenile duck popu- lation prior to the hunting season. Per- haps adults are more susceptible to botu- lism than juveniles, or perhaps there were differences in age composition between the duck populations on these two marshes, which are about 25 miles apart. Such dif- ferences were reflected in hunters' bags checked on the two marshes, tables 55, 56, and 57. Further study of the composition of Utah duck populations seems very de- sirable, because of the differences in age ratios and the importance of seasonal in- fluences on age ratios in that state. Mallard migration in Utah in six au- tumns of the 1940's, fig, 14, was some- what similar to that in Illinois, fig. 13. Juveniles were most abundant early in the season; their proportion in the bag stead- ily decreased to the November 16-30 pe- riod, after which it remained fairly con- stant. In Utah, the age pattern of mi- grating pintails tended to reflect that of migrating mallards, fig. 14. The green- winged teal showed a rather steady de- crease in the relative number of juveniles as the season progressed, while the shov- eler had a ratio of adults to juveniles that remained about the same throughout the season. Thus, in the selection of strategic sites for collecting age data on ducks, and in the evaluation of age ratios, migration schedules of waterfowl must be consid- ered. In some species, much of the migra- tion occurs outside of the hunting season ; in such species, age ratios calculated from data collected from hunters' bags may not be representative of the populations. Un- 100 75- MALLARD ::::x Adults 100 75 z ^50 tr UJ 25 100 75- 50 15-31 1-15 16-30 1-15 OCTOBER NOVEMBER DECEMBER PINTAIL Adults /SHOVELER-:;: Adults :::v::::::::::::::::::#::::M 25 ^. 15-31 OCTOBER 1-15 16-30 NOVEMBER 1-15 DECEMBER Fig. 14.—Juvenile-adult composition of the autumn flights of mallards, green-winged teals, pintails, and shovelers in Utah, as indicated by checks of hunters' bags in the autumns of 1943 19+4, and 1946-1949. 444 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 less traps are operated effectively through- out the period of migration, they, too, will pro\ide biased data. Age ratios obtained from mallards while on their wintering grounds undoubtedly are relatively unbiased by seasonal move- ments. It should not be assumed that a similar statement would be true for all species. For example, in the pintail, birds of the two sexes and ages tend to flock sep- arately in winter, and shifting of these flocks along the Texas coast is common. Regional Variations in Age Ratios Regional variations in the age ratios of ducks first became apparent to the writers when data on the ducks checked in hunt- ers' bags in Utah, Texas, and Illinois dur- ing the fall of 1943 were compared. Since that time, data which provide for further evaluation of regional differences in age ratios have become available, tables 51-57. Mallards.—The juvenile percentage in mallards checked in hunters' bags in each of eight areas of the Mississippi Fly- way is shown in fig. 15. Juveniles made up a large proportion of the ducks that were taken in Manitoba because the adult drakes tend to migrate from there early, and the juveniles are more vulnerable to shooting early in the hunting season than at any other time. It is not known why the juvenile proportion of the mallards taken by hunters in Ohio (the marshes at Sandusky Bay) was so much greater than that taken by hunters in Michigan (the Pointe Mouillee Marsh, which is less than 50 miles from Sandusky Bay). The progressive north to south de- crease in the juvenile proportion of the mallard population, as shown by checks of hunters' bags in Manitoba, the Upper Mississippi areas, the Illinois River valley areas, and the Arkansas areas, table 51 and fig. 15, reflects both a progressive decline in the juvenile population and a decline in vulnerability to hunting as a consequence of increasing wariness among juveniles. 80 I— Fig. 15.—Juvenile percentage in mallards checked in hunters' bags in each of eight areas of the Mississippi Flyway, 1946-1949. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 445 One question of concern to students of age ratios is: "Can age ratios at any one place be used to indicate yearly changes in production?" Table 51 and fig. 16 show the yearly trends in the juvenile propor- tion of the mallard population in a num- ber of areas. Bag checks in Manitoba are in general agreement with those in the Mississippi River basin areas in showing increases in the juvenile component in 1947 and 1948 and a decrease in 1949. Year-to-year differences in the time of de- parture of adults and juveniles from the breeding grounds probably explain some of the differences between mallard age ra- tios taken in Manitoba and those taken in the Mississippi River basin areas. Year-to-year changes in the juvenile proportion of the mallard populations of the Great Lakes areas—principally the Table 51.—Number of juveniles per adult among mallards checked in hunters' bags in 13 regions of North America, 1946—1949. Region 1946 K^C^ 1947 n 1 ^^ ^a. 1948 y^CU 1949 Eq a r=T3 ^ < ^C^ 1946-1949 ^o; The Pas, Manitoba Netley, Manitoba Delta, Manitoba Upper Mississippi River. Wisconsin Michigan Ohio Indiana Illinois River valley Missouri Arkansas Nebraska Utah 1,874 490 333 271 993 1.46 1.29 3.44 2.15 4.84 1,032 903 496 653 287 212 940 14.71 4.17 1.70 2.72 3.95 1.08 3.22 1,317 327 3,350 1.25 1.75 1.16 853 1.16 814 518 3,317 2,514 2,067 2.36 1.76 1.63 1.88 0.66 1,248 251 1,192 820 357 819 369 1,215 408 3,000 1,749 1,216 5.71 5.12 3.00 3.69 1.25 6.04 0.86 3.18 2.92 2.22 1.81 0.74 1,537 893 8.80 2.92 235 1,821 242 735 677 597 1,094 2,104 1,252 1,062 0.93 1.76 1.82 2.62 1.19 0.97 1.04 0.91 0.99 0.88 2,569 3,044 2,621 2,570 3,261 1,082 3,487 1,046 3,943 2,347 11,771 5,515 5,198 10.63 29 62 18 33 50 90 07 77 1.48 1.43 1.60 0.78 Table 52.—Number of juveniles per adult among mallards checked in hunters' bags in Manitoba, Illinois, and Arkansas, 1946-1955 and 1959. 446 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Horicon Marsh in Wisconsin, the Pointe Alouillee Marsh in Michigan, the marshes at Sandusky Bay in Ohio—show h'ttle cor- relation with changes in the Mississippi River basin areas, fig. 16. However, the Great Lakes areas are frequented by only a small proportion of the mallard popula- tion of the Mississippi Flyway ; these areas are to the east of the principal routes used by mallards migrating between their breeding and wintering areas. I'here was reasonably close agreement in the year-to-year fluctuations in the num- ber of juvenile mallards per adult in hunt- ers' bags in the Mississippi River basin areas: the Upper Mississippi River, the Illinois River valley, and the Stuttgart, Arkansas, area, table 51 and fig. 16. There was a highly significant relationship be- tween the age ratios of mallards bagged in the Upper Mississippi River area, Illinois River valley, Missouri, and Arkansas dur- ing the period 1946-1949, table 51, as demonstrated by a correlation coefficient of r= +0.969 or higher, which indicated that the probability that the correlation was due to chance was less than 0.01. The age ratios for mallards bagged in the Illinois River valley were close to those for mallards taken in the Stuttgart, Arkansas, area in all but 2 (1950 and 1953) of 11 years (1946-1955 and 1959), table 52 and fig. 16. The lack of agree- ment in the age ratios from the two areas in 1950 and 1953 is believed to have been related to a delayed hatch on the breeding grounds followed by a somewhat delayed movement of juveniles to Illinois, where a high kill of these young birds occurred. In 1950, mild weather induced large numbers of mallards to remain on the breeding grounds until November 7, when a severe cold front resulted in an unusu- ally large exodus. The ducks moved rap- idly down the flyway, and the adults passed through Illinois without stopping so long as is customary. Because of the unusually rapid movement from the breed- ing grounds to the heavily shot mid-flyway areas, juvenile mallards had not been much exposed to hunting by the time they arrived in Illinois and, thus, were more vulnerable to hunting than in most other years. Fluoroscopy of live-trapped ducks in 1953, in revealing an unusually low per- centage of juveniles with shot wounds, in- dicated that the young of that year, like those of 1950, had not been much exposed to hunting before their arrival in Illinois. 100 90 I- 80 1-70 i^60 S50 40 80 70 60 ^50 ^40 S30 "20 90 1-80 §70 £60 ^^50 Delta Netley MANITOBA MARSH AREAS i -Upper Mississippi MISSISSIPPI BASIN AREAS Ohio Michigan "^-Wisconsin GREAT LAKES BASIN AREAS 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 , Fig. 16.—Year-to-year changes in the juvenile percentage in mallards checked in hunters* bags in each of several areas of North America, 1946-1955. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 447 Table 53.—Number of juveniles per adult in five species of ducks checked in hunters' bags in seven regions of North America, 1948. 448 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 waterfowl populations at the Bear River Mijiratory Bird Refuge in 1946, 1947, and 1948 occurred before the season opened (Van Den Akker (S: Wilson 1951 : 373). Because juveniles in hunters' bags decreased proportionately as the hunting season progressed, fig. 14, the possibility is raised that flights which are top-heavy in juveniles may leave Utah before the hunting season opens. If this assumption is substantiated in subsequent investiga- tions, it would partially account for the abnormally large number of adults in the bags of Utah hunters. No doubt some differences between the age ratios representing various bag inspec- tion stations have resulted from differ- ences in the character and size of areas sampled. In some cases, age ratio data representing a checking station may be from only a single, relatively small area, such as the Delta Marsh or Netley Marsh in Manitoba. In other cases, the data may be from many marshes representing many Table 55.—Number of juveniles per adult in five species of ducks checked in hunters' bags in two areas adjacent to the Great Salt Lake, Utah, in 1947. August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 449 acres. For example, mallards checked at Stuttgart, Arkansas, were shot on at least 20 different swamp or reservoir tracts scat- tered over an area having a 25-mile radius. Most of the mallards checked in the Illi- nois River valley were bagged at 10 clubs distributed over a linear distance of 100 miles. Only a slight difference in the number of juvenile mallards per adult between populations of the upper and lower sec- tions of the Illinois River valley was found in 1939, table 54. This difference was not significant at the 90 per cent level (X2=1.79, 1 d.f.). Much greater differences in number of juveniles per adult for several species of ducks were found between populations of two marshes 25 miles apart and adjacent to the Great Salt Lake, Utah, in 1947- 1949, tables 55-57. The probability that the differences were the result of chance is shown in tables 55—57. There was a sta- tistically significant difference betrween age ratios in the two areas in 11 of 18 tests. These data suggest that the age compo- sition of migrating flocks differs and that fortuitous circumstances result in flocks especially numerous in birds of one age class or the other in a particular marsh. Where only one waterfowl area in a re- gion has been sampled, as Winous Point in Ohio or Pointe Mouillee in Michigan, the age ratios derived may or may not reflect those for the entire region. For species other than the mallard, re- gional data are not adequate to permit evaluation of the age ratios derived in any one area. For each of these species, we have compiled data from as many areas as possible in the Mississippi Flyway on the assumption that data for the total flyway represent the species better than the data from any one area and reflect year-to-year changes in the age composition of the pop- ulation. Factors Affecting Age Ratios Age ratios can be used for appraising the productivity of ducks if the data on which they are based have been carefully evaluated as to the effect of seasonal, re- gional, and shooting biases. Sufficient data for calculating age ratios corrected for differences between juveniles and adults in vulnerabilit}' to hunting have been ac- cumulated for the mallard in the Missis- sippi Flyway, table 58 and fig 17. Most of the data used in the table and graph 3.0 O •* 2.0 (T Ui °- 1.5 en ^i ,.0 UJ > i 0.5 Uncorrected Data Corrected Data 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 Fig. 17.—Uncorrected and corrected numbers of juvenile mallards per adult in bags of Mississippi Flyway hunters in each of several years; uncorrected numbers, 1939-1959; corrected numbers, which compensate for differences in hunting vulnerability between adults and juveniles, 1939-1955. Points on the graph for 1939-1955 are based principally on Illinois data, table 58. Points for 1956-1959 are based on data from Missouri, table 59. Because data for 1955 showed the number of juveniles per adult among Illinois mallards (1.78) to be about 10 per cent less than the number among Missouri mallards (1.99), the point for each year in the period 1956- 1959 represents a figure that is 10 per cent less than the corresponding figure in table 59. +50 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 O"- c ^ 4) in 4) e — 4) 03 0T3 c >• Si ^ 03 >. c— 4>b a .- E o. o .5" " C u o o a +' 7 03 .5§ D.2 C o e •-« 3 3 V C >. 4> -w u 3 uj -J •«. > o; S5 u:z;'->&Ha CO H^Q *> — «Ncsncs-Hcvi-^'«frJ — ^oicscNo <3>i <3 b! Z O S D U " H O O g > 05 Z (J D D W - eS 2 < § ° z M 1^ "^ "^ "^ S z s 05 g w £o s > 5 E " < S > oj :d < I—. •^ iJU ,-s '^OOO—<000—'—'OO^OOO-H lO-HCNrOOO-^—'OO-H cr\TficNooT}HON^-<'^cscsrocNco'^ncscN O ta s > z :d :d - c^Or^o^o^-^oor^loo^csvou^r^cS(N*' 0^0^CT\0^C^C^C^0^OC^^0^C7^0^0^0^0^CT^ -^ ^ o c o u o 3T3 ^ *T3 W L. > Q^ O qj U 3 rt 3 o c " S__ c =» *" - 5^0 raT3 •;: g e S > I August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 451 were collected in Illinois, from both Illi- nois River and Mississippi River areas. Data from Arkansas were used for 1950 and 1953 because unusual breeding grounds and migration conditions in those years had less influence on the migration in that state than in Illinois. Data from Missouri were used for 1956—1958 be- cause no data were available for Illinois in those years and because data from both states for 1955 permitted correction of the Missouri data. An appraisal of the effect of seasonal, regional, and hunting bias on the age ratios calculated for the mallard in the Mississippi Flyway is given below. Seasonal Bias.—Age ratios have been determined for large numbers of popula- tion samples by inspection of ducks in hunters' bags throughout many hunting seasons in Illinois. Although the Illinois hunting seasons have varied as to open- ing date and length, most of each south- ward mallard migration has occurred dur- ing the open season (Bellrose 1944:346— 50). Inasmuch as sample size was de- termined partly by hunter success, which in turn was determined partly by popula- tion size, the numbers of birds in the samples were approximately proportional to the numbers of birds in the populations sampled. For these reasons, we believe that in most years there was little, if any, seasonal bias in the age ratios derived from checking mallards in hunters' bags in Illinois. Regional Bias.—Unpublished popula- tion data and records from the recovery of bands indicate that the largest segments of the mallard population in the Missis- sippi Flyway visit the Illinois River val- ley. The ducks in hunters' bags have been examined each year at numerous places throughout the valley, thereby minimizing the effect of data obtained from aberrant local concentrations of particular age groups. In 1950, an abnormal migration resulted in relatively large numbers of adult mallards passing more rapidly than usual through the Illinois River valley. In both 1950 and 1953, juvenile mallards appeared unusually vulnerable to Illinois hunters. We believe that the duck kill checked in Arkansas provided the more valid data for the Mississippi Flyway in 1950 and 1953, and we have used Arkansas data, derived from table 49, for calculating the numbers of mallard juve- niles per adult for those years. For the other years included in table 52, the differences between Illinois and Arkansas in number of juveniles per adult were not so great as to warrant special treatment of the data. Hunting Bias.—The year-to-year vari- ations in the vulnerability figures for mal- lards, table 39, make it desirable to evalu- ate the age ratios, or number of juveniles per adult, derived from inspection of hunters' bags. Most of the band recovery data from which the ratios of adult to juvenile vul- nerability were derived, table 39, were obtained from ducks banded at the Chau- tauqua National Wildlife Refuge, which is in the center of the area in which bagged ducks were sampled for age. Because no ducks were banded at Chautauqua in 1945 and 1946, in those years banding data from McGinnis Slough, table 40, were used, and adjustments, based on several years of vulnerability rates, were made for differences between the two stations. Because the Arkansas kill data for 1950 and 1953, table 49, were believed to be more valid than the Illinois data, the numbers of juveniles and adults inspected in hunters' bags in Arkansas were chosen as base figures for these years, table 58. The 1 :1.27 ratio of adult to juvenile vulnerability for 1950 and 1953, table 58, was assigned rather arbitrarily. As table 44 indicates, mallard juveniles are about half as vulnerable to hunting in December as in November. Illinois data for several years showed that the dif- ference between adult and juvenile mal- lard drakes in vulnerability to hunting averaged 0.54 (1:1.54 ratio, table 39). The largest part of the Illinois mallard kill was in November. In December, when the birds were in Arkansas, the difference between the adult and juvenile kill figures should have averaged about half of 0.54, or 0.27, and the ratio of adult to juvenile vulnerability should have averaged about 1 :1.27. Table 58 shows for each year in the period 1939-1955 the ratio of adult to juvenile vulnerability among banded mal- lard drakes and the actual (uncorrected) number of juveniles per adult checked in hunters' bags in the Mississippi Flyway, 452 Illinois Natural History Survlv Bulletin Vol. 27, Art. b principally Illinois. It is apparent that the ratio of adult to juvenile vulnerability has no correlation with the number of juveniles per adult baj:;^ed by hunters. Table 58 shows also for each year the number of juveniles per adult and per adult hen amonj; mallards checked in the bags of Mississippi Flyway hunters, each number corrected for the greater vulner- population between the breeding grounds and Illinois. Both shrinkage in the juvenile segment of mallard populations and seasonal de- clines in the vulnerability rates of the juveniles are indicated by the progressive- ly smaller relative numbers of juveniles in hunters' bags as the ducks moved down the fivwav from Manitoba to Illinois to 0.8 1.0 JUVENILES 1.4 ADULT 6 1.8 BREEDING 2.0 2.2 GROUNDS 2.4 Fig. 18.—Numbers of juvenile mallards per adult on the breeding grounds just prior to the hunting season, as calculated from numbers of juveniles per adult in Illinois during the hunting season ; each of the Illinois numbers on which curves A , B, and C are based has been adjusted to compensate for a greater shooting loss among juveniles than among adults before reaching Illinois: A, 2.0 juveniles per adult, B, 2.5 juveniles per adult, and, C, 3.0 juveniles per adult. ability of juveniles. For the period 1939— 1955, the corrected figure was 0.95 juve- nile per adult and 2.7 juveniles per adult hen. These figures probably reflect the age composition of mallard populations in the Illinois River valley for the 17-year period quite well, for inaccuracies in the yearly vulnerability rates would tend to cancel each other out over the period. Trends in the age composition of mal- lard populations in the Illinois River valley reflect trends in the age composi- tion of mallard populations on the breed- ing grounds prior to the hunting season. However, population figures obtained in Illinois do not represent the true age composition of the populations on the breeding grounds, because of the compara- tively greater loss from hunting experi- enced by the juvenile segment of the Arkansas, table 52. Juvenile mallards are undoubtedly more vulnerable to hunters in Manitoba than to hunters in Illinois, and to hunters in Illinois than to hunters in Arkansas, as shown by seasonal changes in vulnerability ratios, table 44. Shrinkage in the juvenile segment of mallard populations between the breeding grounds and Illinois is indicated not only by data in table 52 but by rather abstruse calculations employing band recoveries, mortality rates, and juvenile vulnerability rates, as discussed below. An average annual mortality rate for adult drake mallards in the Mississippi Flvway of about 40 per cent has been derived from band recoverj'^ data for drake mallards banded as adults at Lake Chautauqua, Mason CountA% Illinois, 1939-1944 (Bellrose & Chase 1950:9). August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 453 It seems reasonable to assume that hunt- ing accounts for about three-fourths of this average annual mortality and other causes for one-fourth, or an average an- nual mortality rate of 30 per cent from hunting and 10 per cent from other causes. An analysis of 6,000 indirect (after the year of banding) recoveries of adult drake mallards banded at Lake Chautauqua dis- closed that 47.6 per cent or about one-half of the recoveries were from points north of the Illinois River valley. It seems reasonable to assume further that hunting results in approximately a 15 per cent reduction in the numbers of adult mal- lards before they reach the Illinois River valley from the breeding grounds. Data in tables 44 and 47 suggest that the juveniles are 2 to 3 times as vulner- able as adults during the early fall season when in migration from Manitoba to Illinois. If we assume that juveniles are 2.5 times as vulnerable as adults, and that hunting takes a toll of 15 of each 100 adults before the flights reach Illinois, then we may say that hunting takes a toll of 2.5 times as many juveniles or 37.5 of each 100 juveniles in the same period. Fig. 18 shows a scale for converting the age ratios of mallards occurring in wild populations in the Illinois River valley to age ratios which would be com- parable for wild populations on the breed- ing grounds prior to the hunting season. Following is an example showing the method used to determine a point on the scale, fig. 18, representing the probable number of juveniles per adult on the Canadian breeding grounds when 0.6 juvenile per adult has been determined to exist in mallard populations in Illinois; the adults are assumed to have been sub- jected en route to Illinois to a shooting loss of 15 per 100 and the juveniles to a shooting loss of 37.5 per 100. When A = the number of adults on the breed- ing grounds per adult in Illinois, with a presumed 1:0.6 ratio of adults to juveniles in Illinois, a = the number of adults to 0.6 juve- nile in Illinois, p = the per cent of the adult popula- tion remaining after a 15 per cent loss en route to Illinois, tht A 1 1.18, p 0.85 the number of adults on the breed- ing grounds to 1 adult in Illinois. When Y = the number of juveniles per adult on the breeding grounds, with a presumed 1:0.6 ratio of adults to juveniles in Illinois, y = the number of juveniles to 1 adult in Illinois, p = the per cent of the juvenile popu- lation remaining after a 37.5 per cent loss en route to Illinois, the Y = 0.6 = 0.96, 0.625 the number of juveniles on the breeding grounds to 0.6 juvenile in Illinois. Thus, when there is a ratio of 0.6 juve- nile per adult in Illinois, the adults have been subjected to a 15 per cent loss en route to Illinois, and the juveniles have been subjected to a shooting loss 2.5 times as great as that of adults, the ratio on the breeding grounds is 0.96 young to 1.18 adult, or 0.81 juvenile to 1 adult. An average of 0.95 juvenile per adult was calculated for mallard populations in the Mississippi Flj'way, principally Illi- nois, over a 17-year period, 1939—1955, table 58. This average takes into account differences in vulnerability between adults and juveniles. If juveniles suffered a loss of 37.5 per cent en route, the calculated average number of juveniles on the breed- ing grounds just prior to migration per 0.95 juvenile arriving in Illinois was 1.52 (0.95^0.625). If adults suffered a loss of 15 per cent en route, the calculated average number of adults on the breeding grounds just prior to migration per adult arriving in Illinois was 1.18 (1.0^-0.85). For the 17-year period, the calculated average number of juveniles per adult on the breeding grounds just prior to migra- tion was 1.29 (1.52^1.18). If the average number of juveniles per adult in Illinois (0.95) is to the number of juveniles per hen in Illinois (2.7), table 58, as the number of juveniles per adult on the breeding grounds (1.29) is 454 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 59.—Number of juveniles per adult among mallards shot at the Duck Creek Wildlife Area, Puxico, Missouri, 1955-1959.* Year August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 455 the Pacific Flyway for 11 years, 1949- 1959, fig. 19, reveals for most years an unexpectedly close agreement between the production trends of the two species. The extent of agreement in production trends between the two species is especially remarkable when differences in distribu- tion and habits of the species are con- sidered. The pintails of the Pacific Fly- way breed largely in the western part of the northern plains, whereas the mal- lards of the Mississippi Flyway breed largely in the eastern part of the northern plains. Moreover, mallards are more prone to nest in the Aspen Parklands and the northern mixed Coniferous Forest than are pintails, which are for the most part confined to the grasslands. Factors responsible for the yearly fluc- tuations in mallard production appear to have fairly consistent simultaneous effects on pintail production. Discovery of this fact justifies the use of Mississippi Fly- way mallard age ratios as criteria for eval- uating the accuracy of breeding ground surveys and the effect of environmental conditions on over-all duck production. Because breeding grounds surveys have been used in the past to provide most of the waterfowl production information on which annual hunting regulations have been based, and will undoubtedly be used for a similar purpose in the future, an appraisal should be made of the validity of these surveys. Breeding grounds surveys are affected by the vastness of the breeding grounds, shifts in waterfowl populations with changing water conditions, and difficulty in finding and counting broods. Age ratios obtained from ducks bagged on and south of the breeding grounds provide a means for evaluating the validity of waterfowl breeding grounds surveys and in them- selves serve as measures of production. We have attempted to appraise the validity of breeding grounds surveys by comparing the results of surveys on the plains of Manitoba and Saskatchewan with the mallard age ratios obtained through inspection of hunters' bags in the Mississippi Flyway, principally Illinois. Banding of ducks on the breeding grounds has demonstrated that most of the Missis- sippi Flyway ducks breed in Manitoba and Saskatchewan. The first comprehensive breeding grounds surveys were made by the U. S. Fish and Wildlife Service in 1947. In that year, although the nesting population was reported "fair" for Saskatchewan as a whole, brood production was not corres- pondingly high (Lynch 1948:33). In the same year, the duck crop in the pothole country of Manitoba was considered good, but the production in other types of nest- ing area was "moderate to very poor" 1949 1953 1955 1957 Fig. 19.—Year-to-year changes in the num- bers of juveniles per adult in two species, the data derived by two methods in two areas: pintails trapped in the Pacific Flyway and mallards checked in hunters' bags in the Mis- sissippi Flyway, 1949-1959. (Hawkins 1948:52). Yet, in 1947, mal- lard age ratios from the Mississippi Fly- way showed a pronounced increase in juveniles over the number in 1946, fig. 17. A year later, 1948, "good production" was reported, and "moderate improvement in the waterfowl output for Manitoba" was forecast, by Hawkins & Cooch ( 1948 : 97) ; a small increase in the duck popula- tion of Saskatchewan was recorded by Soper (1948:63). Mallard age ratios ob- tained in the Mississippi Flyway in 1948 showed a further increase in the number of juveniles per adult to a new peak, fig. 17. In 1949, mallard age ratios from the Mississippi Flyway indicated that a sharp drop had occurred in the relative number of young, fig. 17. From the breeding grounds, Hawkins (1949:64) reported that, in Manitoba, nest success was well below that of 1948. Lynch (1949:52) re- ported a reduced nesting population in Saskatchewan as a whole, but a successful 456 Ii.i.iNois Natural History Survey Bulletin Vol. 27, Art. t) hatch in the Aspen Parklands, where mal- lards from the drought-stricken south- western part of the province had moved to join the ducks that normally nest in the Parklands. In 1950, Mississippi Flyway age ratios disclosed a further drop in the number of young mallards per adult, fig. 17. On the breeding grounds, Hawkins (1950:45) concluded "that Manitoba produced con- siderablv fewer ducks in 1950 than in 1949." in Saskatchewan, Colls (1950:40) reported "evidence of a lack of, or an un- successful attempt at, first nesting among mallards and pintails," and added that by the end of July there appeared to be no important attempts at second nesting by these two species. In 1951, mallard age ratios derived from bagged ducks in the flyway indicated a marked increase in the production of young, fig. 17. Hawkins, Gollop, & Wel- lein (1951 :49), reporting on other species as well as the mallard in Manitoba, wrote, "the juvenile crop probably doubled the previous year's." Colls & Lynch (1951: 40), after observing the success of the first nesting attempt in Saskatchewan, wrote that "a more than usually success- ful waterfowl-rearing season" was antici- pated for the area. In 1952, the flj-way age ratios indicated a decline in the number of young mallards per adult. From one Canadian province, Hawkins & Wellein (1952:64) reported: "Manitoba's contribution to the fall flight of 1952 should be about one-fifth less than in 1951." From Saskatchewan, Gollop, Lynch, & Hyska (1952:37), following a survey in July, 1952, reported a potential production "almost twice that of last year." A decrease in the production of young in 1953 was reflected by age ratios for mallards bagged in the Mississippi Fly- way and by field observations in the area. Moderate decreases were reported in Manitoba by Hawkins (1954:76) and in Saskatchewan by Lynch & Gollop (1954: 49). Age ratios for mallards bagged in the Mississippi Flvwav showed little change from 1953 to 1954, fig. 17. For 1954 on the breeding grounds, predictions made after a summer census were that the fall flight of ducks from southern Manitoba would be "about the same as last year," but that a "noticeable" reduction would occur in size of flights from northern Manitoba and from both northern and southern Saskatchewan (Crissey 1954:59, 62, 37). In 1952, John J. Lynch of the U. S. Fish and \Vildlife Service developed mathematical formulas for forecasting waterfowl production in Saskatchewan (Gollop, Lynch, & Hyska 1952:37 and charts 1 and 2). From the formulas he 250 - - 2.0 D 1949 1951 1953 1955 1957 1959 Fig. 20.—Relationship between age ratios of mallards in autumn and the hatch on the breed- ing grounds in the previous spring, as indi- cated by number of juvenile mallards per adult in hunters' bags in the Mississippi Flyway, principally Illinois, 1949-1959, and forecast indices of duck production in Canada (Lynch forecast indices, Gollop, Lynch, & Hyska 1952: 37), the indices derived from breeding grounds surveys in Manitoba, 1953-1959, and Saskatche- wan, 1951-1959. derived forecast indices, one as of June 1 and another as of August 1. The August index was based upon July data : number of broods per square mile, number (per square mile) of late-nesting pairs and single drakes and hens which supposedly represented late-nesting pairs, number of ponds per square mile, number of duck- lings per class III (almost completely feathered) brood, and number of class II (partially feathered) and class III broods per square mile. An index rating of 100 was deemed satisfactory ; an index rating of 300 was deemed perfect. Later, some minor modifications were made in the formulas. A mimeographed report, "Waterfowl Breeding Ground Survey Report, 1958," compiled by Arthur S. Hawkins for the U. S. Fish and Wildlife Service, provides a comparison of late season forecast in- dices for Saskatchewan, 1951-1958, and for Manitoba, 1953-1958. A similar re- August, 1961 Bellrose et al.: Sex Ratios and Age Rat lOS 457 959 Fig. 21.—Estimated numbers of mallards in various parts of the Canadian breeding grounds in May, 1953-1959. port compiled b}^ Hawkins in 1959 pro- vides data on breeding grounds forecasts for that 3^ear. The production forecast indices for Saskatchewan and Manitoba may be compared with the number of juvenile mallards per adult as checked in the bags of Mississippi Flyway hunters, fig. 20. For the period 1952-1959, the popula- tion curve plotted from the forecast in- dices of waterfowl production in Saskatch- ewan was similar to the curve plotted from the Mississippi Flyway age ratios for mallards, fig. 20. However, for the years 1955 through 1958, and especially for 1958, the forecast indices showed con- siderably higher production than was shown by the age ratios, fig. 20. Manitoba forecast indices showed very little correlation with mallard age ratios from the Mississippi Flyway, fig. 20, For example, in 1957 and 1958, Manitoba forecast indices pointed to an increasing production of young; yet the mallard age ratios from the Mississippi Flyway pointed to a decreasing production of young. That there is only slight correlation may be ascribed to Manitoba's relatively small contribution of mallards to Illinois and adjoining states. Aerial surveys made on the breeding grounds in May indicate that about six times as many mallards nest in the plains and parklands of southern Saskatchewan as in the plains and park- lands of southern Manitoba, fig. 21 ; the Saskatchewan contribution to the Missis- sippi Flyway kill is larger than that of Manitoba, even though much larger num- bers of Saskatchewan mallards than of Manitoba mallards are killed in the Central and Pacific flywavs (Cartwright 1956:14-5, 17-8, 20-i). ' For 8 years, beginning with 1952, Saskatchewan breeding grounds indices showed production trends similar to those derived from mallards shot by hunters in the Mississippi Fh^vay, fig. 20. Informa- tion on breeding grounds success of ducks in Saskatchewan in 1951 was somewhat contradictory. The report by Colls & Lynch (1951 :40) indicated "a more than usually successful waterfowl-rearing sea- son." The forecast index for 1951, al- though above 100 and therefore "satis- factory," indicated a production that was low compared to that of most other years of the period 1949-1959. We are in- clined to believe that some mechanical error was made in calculating the 1951 forecast index for Saskatchewan. During the period 1949-1954, duck production as determined from breeding grounds surveys in Manitoba showed a fairly close relationship to production as 458 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 determined from age ratios of mallards shot in the Mississippi Flyway, principally Illinois. However, production as deter- mined by the forecast index in Manitoba showed no positive correlation with pro- duction as indicated by age ratios of ducks shot in the Mississippi Flyway; dia- metricallv opposite production trends were indicated for 1954, 1955, 1957, and 1958, fig. 20. The mallard flight reaching Illi- nois from Manitoba, compared to that from Saskatchewan, may have been so small as to have had little influence on age ratio figures obtained from mallards in- spected in hunters' bags in the Missis- sippi Flyway. One item apparently responsible for bias in the forecast index, especially in Mani- toba, has been the production factor asso- ciated with late-nesting ducks. This factor was included in the index formula to measure the anticipated brood production represented by pairs, lone hens, and lone drakes (believed to be mates of incubating hens) found on the last survey flights, usually conducted in mid-July. The pro- duction from ducks that are actually breeders may be lower than anticipated, and many ducks that are classed as breeders may be through breeding. Charles D. Evans of the U. S. Fish and Wildlife Service and Ralph Hancox of the Mani- toba Game Branch recognized the latter possibility in Manitoba in 1958 (unpub- lished report), when they found abnormal- ly high numbers of molters and premolters on breeding areas. In spite of diligent effort to classify breeders and nonbreeders correctly, Evans and Hancox believed that they included many nonbreeders in their late-nesting index. It is apparent from age ratio data from the Mississippi Fl\^vay that in those years in which there was a major population shift from the Canadian Grasslands north to the lakes and marshes of the Aspen Parklands and Mixed Coniferous Forest production of young declined more than had been anticipated. No doubt some of the differences be- tween production data based on age ratios obtained from bagged ducks in the Missis- sippi Flyway and similar data based on breeding grounds surveys stem from dif- ferences in production between the Grass- lands, the Parklands, and the Coniferous Forest region. Because of difficulty of ac- cess, difficulty in making observations, and a low density of breeding ducks, only cursory duck surveys have been made in the Coniferous Forest region. Hence, the production of mallards from this region is largely unknown but may be larger than suspected. Although the population density of mallards there may be low, this region is so vast that it may well con- tain a sizable breeding population. Other differences between production data from the Mississippi Flyway and data from the breeding grounds surveys may result because the Mississippi Flyway data include only mallards, whereas data from breeding grounds surveys include all species of ducks. Mallards usually make up over half of the breeding popula- tion, but diving ducks and late-nesting species, such as the baldpate and the gad- wall, which may show yearly production trends different from those of the mallard, may influence the production data from the breeding grounds. Production and Environment It is difficult to evaluate the effect of environment on waterfowl production be cause of the vastness of the breeding grounds and the variations in water and weather conditions. Seldom, if ever, are water or weather conditions similar over the entire breeding range. Moreover, an area that is favorable for waterfowl in one year may be unfavorable the next. Nevertheless, a general review of water and weather conditions in Manitoba and Saskatchewan, the principal breeding range of the mallard of the Mississippi Flyway, has been made for the years 1939- 1946 from The Duckological, a news sheet published at irregular intervals by Ducks Unlimited (Canada), with headquarters at Winnipeg, and for the years 1947-1959 from published and unpublished reports of breeding grounds surveys by the U. S. Fish and Wildlife Service and the Canad- ian Wildlife Service. In the following paragraphs the water and weather condi- tions on the breeding grounds for each of the 21 years in the period 1939-1959 are summarized in relation to mallard pro- duction as indicated by the number (un- corrected) of juveniles per adult inspected in hunters' bags in the Mississippi Flyway 1 August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 459 —Illinois and Arkansas, table 58, and Missouri, table 59. Water conditions on the Canadian plains in the spring of 1939 were much improved over those of 1938. Conditions for breeding ducks were good in Sas- katchewan and poor in Manitoba. Most water areas persisted until broods were on the wing. These conditions resulted in a production per breeding mallard (uncor- rected number of juveniles per adult) which was about equal to the average of such production data for 17 years, 1939- 1955, table 58. In 1940, spring water conditions in Manitoba were the worst in the history of that province and in Saskatchewan were poor as far west as the central part. Water conditions were good in western Sas- katchewan. Good rains in June improved many water areas. Mallard production in this year, as in 1939, was close to the average for the 17-year period, table 58. In the spring of 1941, water conditions, although greatly improved over conditions in 1940, were considered fair in Manitoba and ranged from poor to good in Sas- katchewan. Water areas rapidly dried up when such summer rains as fell failed to maintain them. Heavy losses among ducklings occurred as a result of drought. A drop in the number of young per adult bagged in the Mississippi Flyway re- vealed a sizable decline in mallard produc- tion, table 58. In the spring of 1942, water conditions were fair to good in Manitoba; they were bad, fair, or good, depending on the locality, in that part of Saskatchewan where most of the ducks are produced. Heavy spring rains prevailed over most of the plains, and these continued into the summer. The number of young per adult in the Mississippi Flyway, table 58, indicated a moderate increase in mallard production. Spring water conditions in 1943 throughout the Canadian plains were the best in many years, being rated fair over northern Saskatchewan and northern Manitoba and good to excellent almost everywhere in the southern parts of these provinces. In that year, age ratios in the Mississippi Flyway, table 58, indicated a pronounced increase in mallard pro- duction. In 1944, there was "lots of water" in northern Saskatchewan and Manitoba, but in the southern parts of these provinces, where most of the ducks are produced, water levels were largely "dangerously low" to fair. A larger than usual propor- tion of the breeding waterfowl population moved through the Grasslands northward into the Aspen Parklands and Mixed Coniferous Forest. Rains in June re- moved danger of heavy loss of ducklings through drought. Mallard production de- clined markedly to a point below average, table 58. In 1945, spring water conditions were good in Manitoba and all of Saskatchewan but the southwestern part, where few Mississippi Flyway mallards breed. Water conditions in Manitoba remained good for ducks, but southern prairies of Saskatche- wan dried up. Subnormal temperatures occurred through much of April and May, and, in the northern portions of Manitoba and Saskatchewan, ice was still present on marshes and lakes on May 24. Age ratios of ducks bagged on the flyway indicated that mallard production had declined to the lowest point since the studv started in 1939, table 58. In 1946, water conditions were excel- lent in Manitoba and through a belt 100 miles wide in eastern Saskatchewan. June rains improved water conditions in Al- berta and Saskatchewan. May was ex- cessively cold, and heavy frosts occurred. Age ratios from the Mississippi Flyway indicated that mallard production rose considerably but remained below the 17- year average, table 58. More detailed information on breeding grounds conditions became available in 1947, when extensive surveys were in- augurated by the U. S. Fish and Wildlife Service. Salient facts from these surveys have been condensed in tables 60 and 61 and are shown graphically in figs. 22 and 23. These tables and figures, as well as tables 58 and 59, should be referred to in connection with the following paragraphs on duck production and breeding grounds conditions. In 1947, a year in which fair to good water conditions prevailed and slight to moderate water loss occurred during the breeding season in Manitoba and Saskatch- ewan, the number of juveniles per adult 460 Illinois Natural History Survey Bulletin Vol. 27, Art. () -^-:5;~^r ° August, 1961 Bellrose et al: Sex Ratios and Age Ratios 461 in the bags of Illinois hunters revealed a spectacular rise in production by the mal- lard ; the rise occurred even though spring temperatures were below^ normal. The spectacular increase in production con- tinued in 1948, as vrater conditions in Canada improved. In 1949, vt^ater condi- tions in Saskatchew^an w^ere poor, and mallard production dropped drastically. In 1950, water conditions were excel- lent in both Manitoba and Saskatchewan. May of 1950, however, was unusually cold and wet. Mallard production, as in- dicated by age ratios of ducks bagged in the Mississippi Flyway, declined. In 1951, water conditions were good through the breeding season in Saskatchewan and fair in Manitoba ; a major water loss oc- curred in Manitoba. In that year, mallard production increased considerably. The two provinces differed materially in water conditions in 1952. In Manitoba, rapid disappearance of water areas began in April and continued through the summer; by August waterfowl conditions were the worst known since breeding grounds ob- servations were started. In Saskatchewan, water conditions were favorable through- out the breeding season. Mallard produc- tion in 1952 declined very little, if at all, age ratios of bagged ducks indicated. In 1953, water conditions were excellent in Saskatchewan and fair to good in Mani- toba. There was no water loss during the season in Manitoba and only a slight loss in Saskatchewan. Despite these favorable water conditions, age ratios of bagged ducks revealed a decline in the production of mallards in 1953. Although small water areas in Sas- katchewan and Manitoba were almost at maximum numbers in 1954, age ratios indicated only a slight increase in mallard production, fig. 22. In 1955, with a further increase in number of ponds in Saskatchewan, but with a sizable decrease in the number in Manitoba, mallard pro- duction increased materially. Ponds were down in number in Sas- katchewan in 1956, but they increased in number in Manitoba, fig. 22. In that year, age ratios of bagged ducks indicated a 40 1- 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 Fig. 22.—Relationship between water conditions on the Canadian breeding grounds and mallard production, as indicated by the number of ponds per square mile in southern Saskatche- wan and southern Manitoba in May of certain years, and by the number of juveniles per adult checked in hunters' bags in the Mississippi Flyway. Points on the graph representing number of juveniles per adult for 1948-1955 are based principally on data from Illinois, table 58; points for 1956-1959 are based on data from Missouri, table 59. Because data for 1955 showed the number of juveniles per adult among Illinois mallards to be about 10 per cent less than the num- ber among Missouri mallards, each point on the graph for the years 1956-1959 represents a figure that is 10 per cent less than the corresponding figure in table 59. Data for the breeding grounds are from the U. S. Fish and Wildlife Service and the Canadian Wildlife Service. 462 Illinois Natural History Survey Bulletin Vol. 27, Art. b drop in mallard production. In 1957, ponds were down in number in both provinces, and mallard production de- clined. In the following year, 1958, water areas continued down in number in Mani- toba but increased in Saskatchewan ; mal- lard production showed a further decline. In 1959, water conditions in Manitoba remained about the same as the year be- fore, but the number of ponds in Saskatch- ewan declined sharply. For the fourth consecutive year mallard production de- mile in May) followed similar trends in most years of the period 1948-1959, fig. 22. Mallard production and water abun- dance followed divergent trends in 1950, 1953, and 1958. In 1954, mallard pro- duction showed no decisive trend, while water abundance rose markedly. In Manitoba, mallard production tended to parallel water abundance in the years 1956-1959 but not in the 3 years previous. In 1945, 1950, and 1953, when water conditions on the breeding grounds were JUVENILES 1952 1953 1954 1955 1956 1957 1958 1959 Fig. 23.—Relationship between the density of the adult mallard population on the Canadian breeding grounds in spring and the production of young, 1952-1959, as indicated by the number of ponds per mallard in southern Manitoba and southern Saskatchewan in May and by the num- ber of juveniles per adult checked in hunters' bags in the Mississippi Flyway the autumn fol- lowing. Data for the breeding grounds in 1952 represent Saskatchewan only. Points on the graph representing number of juveniles per adult for 1952-1955 are based principally on data from Illinois, table 58; points for 1956-1959 are based on data from Missouri, table 59, as ex- plained in the legend for fig. 22. Data for the breeding grounds are from the U. S. Fish and Wildlife Service and the Canadian Wildlife Service. clined ; the number of juveniles per adult in the Mississippi Flyway, as represented by data from Missouri, was at a 21-year low, tables 58 and 59. No completely objective correlation can be m.ade between waterfowl production and conditions on the breeding grounds. Much of the information from the breed- ing grounds is not of an objective nature; it is not subject to convenient or exact measurement, and the effects of the many environmental variables are not well un- derstood. In Saskatchewan, mallard production (as determined by the number of juve- niles per adult among birds bagged in Illinois) and water abundance (as meas- ured by the number of ponds per square fair to excellent and mallard production was down, temperatures below normal and other unseasonable weather conditions, in- cluding blizzards, occurred as late as mid- May, disrupting the nesting activities of the mallard, pintail, and other early nesters. In 1947, when water conditions were fair to good, and subnormal temper- atures were experienced early in the nest- ing period, mallard age ratios indicated substantially better than average produc- tion. Concerning weather and water condi- tions in Manitoba in 1950, Hawkins (1950:42) reported as follows: If abundant water were the only require- ment of nesting waterfowl, ducks nesting in Manitoba would have had a "banner" year; August, 1961 Bellrose et ah: Sex Ratios and Age Ratios 463 they did not, however, in spite of the greatest spread of surface water in many years. Sub-normal temperatures continued through- out the nesting and brooding season. May was particularly cold and wet, possibly a factor in the poor hatch. From July 12 to 15, when many broods were only a few days old, temperatures dipped almost to the freezing point, perhaps another factor affecting success. Colls (1950:36-7) reported that un- seasonably cold weather prevailed all over Saskatchewan for most of the summer and that the more northerly lake country re- mained ice-bound in some cases as late as the end of May; however, he stated "that weather and water conditions over south- ern Saskatchewan were exceptionally favourable for the 1950 waterfowl popula- tion." Hawkins (1954:75) reported that on April 15, 1953, the worst spring blizzard in many years combined with several days of freezing temperatures to adversely af- fect waterfowl production in Manitoba. Another record-breaking blizzard oc- curred on May 11, and smaller snow- storms on April 24 and May 14 resulted in snowdrifts which could have buried large numbers of nests. Indeed, a few nests that had been buried were found after the snow disappeared. Furthermore, temperatures accompanying the blizzards were sufficiently low to freeze unprotected eggs. In Saskatchewan, Lynch & Gollop (1954:45) reported that May, 1953, was very cold, with much snow prior to the middle of the month. Stoudt & Buller (1954:55) reported that the weather was "wet, cold and miserable for the most part" during the nesting and brooding season, but concluded: "We have always heard of the dire effects of wet, cold weather on newly hatched ducklings but such ill effects were not noted during the 1953 brooding season." A late breakup of ice occurred in Mani- toba lakes in 1954 (Evans 1955:72), with freezing temperatures and snow extending into early May. May and early June were generally cool and wet. Saskatchewan experienced a record- breaking cold wave in late April and early May of 1954 that substantially de- laved nesting bv mallards and pintails (Gollop & Lynch 1955:46-7). As late as mid-May, many lakes were still frozen over. As a result of adverse weather in the spring of 1954, Stoudt & Stinnett (1955: 60) found an extremely high nest loss among mallards as well as other ducks on a small study area in southeastern Saskatchewan. They attributed the loss in the first nesting effort of mallards to a blizzard and zero temperature on May 1. Most of May and June was charac- terized by cold, very wet weather, retard- ing the development of good nesting cover. The paucity of nest cover and the lack of stable food for predators resulted in great- ly increased predation upon duck nests. Flooding destroyed many nests missed by predators. Decreased production by the mallard on the plains of Canada in years of very plentiful water and of cold weather, snow, and heavy rains at nesting time suggests that cold and excessively wet springs may be as unfavorable to duck production as dry and warm springs. It is quite evident that water and weather conditions on the breeding grounds during the nesting and rearing period were major factors contributing to the gross changes in mallard production in 1939-1959. Yet there was another factor in mallard production, population density, that seems to have operated in most years within the broad limits of the environment, and, indeed, that may well have been the dominant regulating factor in production in those few years in which there was a poor correlation between en- vironment and age ratios. In 2 years having similar water conditions but breed- ing populations of different sizes, the num- ber of juveniles produced per breeder may be lower in the year with the larger popu- lation than in the year with the smaller. Several years ago, an inverse relation- ship between population density and pro- duction of young was reported for the muskrat by Errington (1943:877), who stated: "the data indicate that rates of increase tend to vary with particular habitats and inversely with the density of the breeding stock." That an inverse relationship between population density and production could be detected in upland game was noted by several writers (Baskett 1947:25-7; 464 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Bump et al. 1947:540; Errington 1945: Production in the mallard and possibly other duck species may bear, within cer- tain undetermined limits, an inverse rela- tionship to population densities, or a direct relationship to number of ponds per duck. (Increased density in a duck population on the breeding grounds may be brought about by a decrease in the number of water areas as well as by an increase in the number of ducks.) With the exception of 1953 and 1954, years in which cold temperatures and snow reduced production of the mallard, there was a good correlation between number of ponds per breeding mallard and produc- tion of young on the Canadian breeding grounds. As the number of ponds per breeding mallard decreased from 2.0 to 0.6 in the Grasslands and Aspen Parklands of Manitoba and Saskatchewan, produc- tion declined from 1.78 juveniles to 0.54 juvenile per adult, fig. 23. A change in the density of the mallard population on the breeding grounds may afifect production in two ways : ( 1 ) alter the rate of nest destruction and desertion ; (2) alter the relative number of ducks that can be accommodated by prime breed- ing habitat. Sowls (1955:74) found that most mal- lards nest within 100 yards of pond, slough, or lake margins rather than at greater distances from water. The area of nest concentration adjacent to a body of water has been called the nesting zone. As ponds and other small water areas decline in number, greater concentrations of mallard nests occur in the nesting zones of the bodies of water that remain. It is probable that, as nest density increases, the rate of nest loss rises. Although data on the relationship between nest density and nest loss are lacking for waterfowl, Stokes (1954:36) found that in pheasants nest abandonment increased with breeding density. Unpublished field studies by Alex Dzubin (letter March 5, 1960) of the Canadian Wildlife Service suggest that space requirement also may be related to mallard production. Dzubin believes that, through interactions involving both ag- gressive and sexual behavior, pairs of mal- lards space themselves over the breeding grounds. Adequate spacing is most evi- dent in the Aspen Parklands region, with its abundance of water areas ; it is less evident in the Grasslands region, which may have a scarcity of water areas. Space behavior of ducks around waiting areas tends to place a limit on the number of pairs any one area can accommodate. The role of space in regulating the size of breeding populations of waterfowl is apparent in an analysis made by Schrocder (1959:4—5) of water areas and numbers of breeding ducks in North Dakota. Schroeder found that the numbers of breeding ducks and water areas tended to fluctuate up and down together. For example, in 1950, water areas numbered 11.4 and breeding ducks 24.6 per square mile, whereas, in 1959, water areas had declined to 2.1 per square mile and ducks to 8.4 per square mile. Evans & Black (1956:52) found a direct relationship between water areas and breeding ducks on an 11.25-square- mile prairie pothole area in South Dakota. Their study showed that as the number of potholes with water on May 10 in- creased and then decreased from 1950 through 1953 so did the number of breed- ing pairs of ducks. Stoudt (1959:103) reported a direct relationship "up to a certain point" be- tween numbers of breeding ducks and numbers of water areas on a study area 40 miles long and one-eighth mile wide near Redvers, in southeastern Saskatche- wan. He did not find this direct rela- tionship in "extremely wet years and extremely dry years." From 1953 through 1958, there were only small variations in the number of water areas each year on May 1 in a Lousana, Alberta, study area, but the number of breeding pairs of mallards on this small area rose from 103 to 338 dur- ing that period (Smith 1959:3, 8). The number of ponds on May 1 decreased fromj 198 in 1958 to 131 in 1959 and the num- ber of breeding pairs from 338 to 241. The smaller a study area, the less likelyJ it is to show direct relationships between| the numbers of breeding pairs and the numbers of water areas. Local variations in mortality rates, homing, and populatior saturation levels that grossly affect thel data for small areas may have no appreci- August, 1961 Bellrose et ai: Sex Ratios and Age Ratios 465 able effect upon the data for extensive areas, because the many local variations in the extensive areas tend to cancel each other. Because the space behavior of ducks limits the number of breeding pairs that a given waterfowl habitat can accom- modate, when an increase occurs in the breeding population of an area that has reached the limit of its carrying capacity, or when a decrease occurs in the number of ponds on the area, some of the ducks associated with the area must do one of two things: (1) move to other areas not occupied to the saturation level or (2) fail to reproduce. The areas to which the ducks move may be of poorer quality for the production of young than the areas occupied to the saturation level. Biologists have long been aware of the tendency of bird populations to make maximum use of the best available habitat before occupying less favorable habitat. On a Saskatchewan study area, Stoudt (1952:55) found that breeding pairs of ducks tended to make maximum use of the small water areas ( 1 acre or less) and shift to less favorable habitat when the prime areas were occupied to the limit of their carrying capacity. Under conditions associated with popu- lation or habitat changes, ducks may move from a region of basically good habitat to a region of inferior habitat. In 1959, there was an increase in the number of mallards found during May in the marshes of the Coniferous Forest in northern Alberta and other northern parts of Canada and a decrease in the number found in southern Saskatchewan. The Coniferous Forest lacks the quality habitat for nesting mallards supplied primarily by the Grasslands and secondarily by the Aspen Parklands. Biologists have noted that under severe crowding many ducks do not breed and that some ducks that make attempts at nesting do not make further attempts if the first attempts fail. Arthur S. Hawkins and Gerald Paspichal in an unpublished report of the U. S. Fish and Wildlife Service on the 1959 breeding season in the pothole country of western Manitoba noted that many ducks in that area were individuals that had been displaced from other areas. They found indications that some ducks did not attempt to nest and that others did not make the usual re- nesting attempts after having lost nests. Stoudt (1959:104) observed that many pairs of ducks in southeastern Saskatche- wan in 1959, a year of very low water levels, "did not seem to nest at all." Fig. 17 may be interpreted as showing that when the Grasslands and Aspen Park- lands have reached the limit of their carry- ing capacity as a result of population in- creases and/or habitat deterioration, the production of juveniles per adult mallard declines for 2 to 4 years, until the breed- ing population has declined to a point where population density is no longer a limiting factor. Then, when a decrease in population or an increase in water areas results in more space per breeding pair, the production of young per breeder in- creases for 1 to 3 years, until population density again becomes a limiting factor. The highs and lows in a breeding popu- lation of mallards may lag 1 or 2 years behind the highs and lows in the produc- tion of young per breeder. The first year a high breeding population produces a smaller number of young per breeder, the over-all population will probably con- tinue to increase because of the large number of breeders still present to produce young. The over-all population may con- tinue to increase even into the second year of lower production. When the breeding population is at a low point, the over-all population will probably continue to de- cline for a year after an increase in pro- duction, as the increased number of young per breeder may fail to result in as many young as are needed to replace the ducks lost through hunting and natural mortal- ity the previous year. The foregoing analysis of the effect of environment on production of mallards and other ducks points up the importance of water areas that are available to breed- ing pairs. Also, it points to abnormally low temperatures and associated weather conditions in April and May as factors of major importance in production. Ab- normally low temperature conditions do not occur on the breeding grounds as frequently as abnormally low water condi- tions. Within the framework of accept- able nesting environment, and within certain undetermined population limits, 466 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 Table 62.—Number of juveniles per adult hen (the number corrected for the greater vul- nerability of juveniles to hunting) in each of 12 species of ducks checked in hunters' bags in the .Mississippi Flyway. principally Illinois, 1946-1949. Species August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 467 vest of birds without undue depletion of populations. Age ratios obtained through inspection of ducks in hunters' bags offer valuable assistance in determining the well-being of populations and in evaluat- ing the extent to which production may be expected to replace annual losses. An average annual production of 2.7 young of flying age per adult hen has been estimated for mallards of the Mississippi Flyway in the period 1939-1955, table 58. Although this average figure and other production figures shown in table 58 are for the mallard only, they are of value in making over-all hunting regulations be- cause mallards comprise about half of the duck population. Major year-to-year changes in produc- tion of the mallard, changes that probably are present in other species also, require flexibility in regulations governing the duck kill. Production data from age ratios need to be supplemented by information from the breeding grounds in the northern part of the Mississippi Flyway. More informa- tion is needed on the effect of different combinations of regulations on mortality in the mallard and other species of ducks. Bellrose & Chase (1950:22) found evi- dence that natural losses plus hunting losses occurring under the regulations in force in the years 1939-1947 resulted in an annual mortality rate of about 48 per cent in male mallards; the annual mor- tality rate of the entire population was somewhat higher. The extent to which increased produc- tion in ducks can compensate for in- creased mortality is at present pure speculation. The ability of animals to compensate for annual variations in mor- tality rates by flexibility in production is widely recognized. More than 80 years ago, Forbes (1880:9) wrote: "The fact of survival is . . . usually sufficient evi- dence of a fairly complete adjustment of the rate of reproduction to the drains upon the species." A few years ago, Allen (1943:113-4) cited the resilience of the fox squirrel in compensating for severe losses in number. Bump ef al. (1947 : 539— 40) reported for the ruffed grouse (Bon- asa umbellus) in New York "a distinct tendency for greater relative increases to be associated with lower breeding popula- tions." Diem ( 1959: 304-5), in reporting on duck production in an Alberta study area, stated that some years "having low breeding populations have witnessed bumper crops of young." The probability that ducks have some degree of elasticity in their capacity to reproduce is shown by differences in pro- duction among various species. It is shown further by differences in production be- tween the ducks of different flyways. Although age ratios for Nebraska mallards have tended to follow the same general trend from year to year as those in Illinois, they have consistently reflected lower num- bers of juveniles per adult, fig. 16. There is good evidence from banding and from the percentage of birds carrying shot wounds that shooting pressure is lighter in the Central Flyway (and, therefore, that the mallard undoubtedly has a lower mortality rate in that flyway) than in the Mississippi Flyway. Perhaps the ap- parently lower reproduction rate of mal- lards in the Central Flyway is the result of the lower mortality rate there. More data are needed on production and mortality rates in various species of ducks in each of the four flyways. By com- paring production and mortality rates in various species of ducks in each of the four flyways, it would be possible to learn a great deal more than is now known about an apparent inverse relationship between mortality and production and the opera- tion of other population mechanisms of waterfowl. Waterfowl population research requires a more concerted effort to appraise pro- duction and to relate this to habitat condi- tions. We recommend that state and federal biologists, working through the four flyway councils, make detailed and uniform appraisals of conditions on the breeding grounds and that, by use of age ratios obtained from bagged ducks, they determine yearly production for the im- portant species. The most feasible approach to the problem of obtaining data on age ratios appears to entail the establishment of sta- tions where large samples of particular species could be obtained. Some samples should be taken where there is evidence that a cross section of the migrating popu- lation can be obtained or where the win- 468 Illinois Natural History Survey Bulletin V..1. 27, Art. 6 tcrinp populations exhibit a minimum of regional bias. In some areas, a station mi^ht be established at which the age ratios for only one species of duck are taken. For example, in the Mississippi Flyway, the best station for sampling the mallard mi>iht be Stuttgart, Arkansas; the best for the gadwall. Mobile Delta, Ala- bama; the best for the pintail and the green-winged teal, the coastal marshes of Louisiana ; the best for the ring-necked duck. Reelfoot Lake, Tennessee; the best for the redhead and the canvasback, Lake St. Clair and the Detroit River, Michigan. SUMMARY 1. The present study is an evaluation of sex and age ratios in North American duck populations and the ways in which, in waterfowl management, these ratios can be used to measure productivitv. (Page 391.) 2. Determination of sex composition in duck populations presented a difficult sampling problem complicated by differ- ences in species, seasons, and places, and bv inadequate sampling techniques. (Page 393.) 3. In the study reported here, most trapped or bagged ducks that could not be readily sexed by plumage differences were sexed by cloacal characters. (Page 396.) 4. Four methods of sampling water- fowl populations for sex ratios were used : (1 ) examination of trapped ducks, (2) in- spection of ducks taken by hunters, (3) observation of ducks in the field, and (4) examination of disease victims. Biases evident in each method were recognized, and corrections were made whenever pos- sible. (Page 396.) 5. Baited, funnel-type traps tended to take disproportionate numbers of drakes, while gate-type traps placed on shore tended to catch a predominant number of hens. (Pages 397, 400.) 6. Inspection of ducks in hunters' bags made possible the separation of drakes and hens in molting adults and in juve- niles. (Page 400.) 7. Most sex ratios derived from inspec- tion of hunters' bags showed little bias, usually in favor of drakes. (Page 400.) 8. Banding records indicated that mal- lard drakes were 1.05 times as likelv to be shot by hunters as were hens, the dif- ferential probably a result of hunter pref- erence for drakes. (Page 401.) 9. A few field observations on living ducks in spring were used to provide sex data on samples of several species ; how- ever, because it is almost impossible to make a sufficient number of random ob- servations to insure an adequate sampling of the population of a flyway or other large area, field observations were not more extensively used. (Pages 401-2.) 10. The validity of sex ratios obtained from examination of ducks that were vic- tims of disease was found to need further study. (Page 402.) 11. Analysis of available data showed no significant departure from an evenly balanced sex ratio in ducks at fertilization or at hatching. (Pages 402-3.) 12. Data obtained from examining juvenile ducks trapped during the breed- ing season or taken by hunters during the fall indicated that the ratio between the sexes from the time of hatching to adult- hood was close to 50:50; local variations appeared to result from differences in sea- sonal movements. (Pages 403—5.) 13. Although sex ratios of adults usu- ally- favored drakes, there were numerous exceptions. ( Pages 405—6. ) 14. Sex ratios of many species of ducks varied from week to week in any given area as the composition of the local popula- tion changed with the arrival and de- parture of flocks containing varying num- bers of drakes and hens. (Page 408.) 15. In most species of ducks for which data were available, drakes made up a smaller proportion of the hunters' kill in Manitoba than in three states to the south (North Dakota, Illinois, and Tennessee), indicating that more drakes than hens left Manitoba in advance of the hunting sea- son. Among adult mallards bagged in Illinois, there was a steady increase in the drake segment through the third week in November, followed by a period of stabi- lized sex ratios, and then further increase in the drake segment of the wintering population, usually present in Illinois after the first week in December. In Utah, sex ratios of adult mallards bagged by hunters were relatively stable throughout fall. In only a few species did there appear to be differences in seasonal movements between August, 1961 Bellrose et al.: Sex Ratios and Age Ratios 469 drakes and hens in the juvenile class. (Pages 408-9.) 16. Periodic counts of ducks in late winter and early spring revealed differ- ences in the sequence of northward migra- tion of drakes and hens of the same species. (Pages 411-16.) 17. The first spring flights arriving in Manitoba showed, with minor exceptions, a closer approach to a balance between sexes than did subsequent populations. (Pages 416-9.) 18. Sex ratios in ducks were found to vary with migration routes and various areas of their wintering grounds. (Pages 419-20.) 19. Information collected on the prin- cipal mortality factors affecting the North American duck population indicates that hunters and disease take relatively more drakes than hens. This information is not sufficient to permit appraisal of the in- fluence of predation on sex ratios; how- ever, appreciable losses among hens during the breeding season, most of these losses apparently attributable to predation, agri- cultural operations, and stress, may ac- count for the predominance of drakes in the adult class. (Page 426.) 20. Data showed that, the more pro- ductive a species of waterfowl, the greater is apt to be the proportion of juveniles in its population at the opening of the hunt- ing season ; the greater the proportion of juveniles in a population, the more nearly balanced is its sex ratio. (Page 426.) 21. Drakes occurred in relatively greater numbers among diving ducks than among dabblers; however, examination of the available knowledge on the reproduc- tive biology characterizing these two sub- families revealed nothing which suggests that extra drakes may be more important to the maintenance of populations of div- ing ducks than of dabblers. (Page 427.) 22. The study suggested that the value of extra drakes needs investigation through an experimental procedure designed to re- duce the number of drakes in a subpopula- tion of a species having a large drake segment. (Page 428.) 23. Sex ratios that were derived from inspection of mallards in hunters' bags in Illinois provide a fair index to production but not so good an index as age ratios; sex ratios obtained from observations on the breeding grounds in Canada do not appear to provide a more reliable index to production than sex ratios calculated from bag inspections in Illinois. (Page 429.) 24. Age ratios alone, this study as- sumed, are seldom true indices of water- fowl production, but they offer a promis- ing basis for measuring it. (Page 430.) 25. In this study, age ratios were ob- tained by examination of ducks trapped for banding, shot by hunters, or killed by disease. (Page 431.) 26. Although most traps were selec- tive for adults, ducks taken in traps were found to provide a rough index to yearly changes in age ratios. (Pages 431-5.) 27. Juveniles were found to be more vulnerable to hunting than adults; the vulnerability differential varied with place, time of hunting season, vear, and species. (Pages 435-9.) 28. Age ratios obtained from bagged ducks and corrected for the greater vulner- ability of juveniles offered the best means of determining the adult-juvenile compo- sition of duck populations. (Page 439.) 29. Age ratios derived from waterfowl lost to severe outbreaks of disease were considered unreliable because of the ir- regular occurrence and site limitations of such outbreaks. (Pages 439-40.) 30. Because juveniles and adults do not follow identical migration schedules or routes, age ratios showed seasonal and regional variations. (Pages 440-9.) 31. Age ratios were found to be use- ful for appraising the production of ducks if the data on which they are based have been carefully evaluated as to the effect of seasonal, regional, and shooting biases. (Page 449.) 32. A production curve (page 449) that was plotted from corrected age data for mallards in hunters' bags in the Mis- sissippi Flyway for 17 years, 1939-1955, follows a pattern somewhat similar to that plotted from uncorrected data and shows a somewhat rhythmic production trend that may be inherently characteristic of waterfowl populations and prove to be density dependent in origin. (Page 454.) 33. A comparison of mallard age ratios in the Mississippi Fh'way with pintail age ratios in the Pacific Flyway for 1 1 years, 1949-1959, revealed for most years an un- expectedly close agreement between pro- 470 Illinois Natural History Survey Bulletin Vol. 27, Art. 6 duction trends of the two species involved. (Panics 45+-5.) .U. For the period 1952-1959, the population curve plotted from forecast in- dices of waterfowl production in Sas- katchewan was similar to the curve plotted from the Mississippi Flyway age ratios for mallards. Manitoba forecast indices showed very little correlation with mal- lard age ratios from the Mississippi Fly- way, possibly because, as aerial surveys in- dicated, about six times as many mallards nest in the plains and parklands of Sas- katchewan as in the plains and parklands of Manitoba, and because the Saskatche- wan contribution to the Mississippi Fly- wav kill of mallards is larger than that of Manitoba. (Page 457.) 35. An attempt was made to correlate water conditions on the breeding grounds with mallard production. In Sasketche- wan. mallard production (as determined by the number of juveniles per adult among birds bagged in Illinois) and wa- ter abundance (as measured by the num- ber of ponds per square mile in May) fol- lowed similar trends in most years of the period 1948-1959. In Manitoba, mallard production tended to parallel water abun- dance in the years 1956-1959 but not in the 3 years previous. (Page 462.) 36. Decreased production by the mal- lard on the plains of Canada in years of very plentiful water and of cold weather, snow, and heavy rains at nesting time sug- gests that cold, excessively wet springs may be as unfavorable to duck production as dry, warm springs. (Page 463.) 37. Population density, as well as wa- ter and weather conditions on the breeding grounds, seems to have contributed to gross changes in mallard production in 1939-1959; it may well have been the dominant factor regulating production during those years in which there was poor correlation between age ratios and conditions on the breeding grounds. (Page 453.) 38. Age ratios of ducks checked in hunters' bags in the Mississippi Flyway for the period 1946-1949 provided indices of production for the various species. Sev- eral species appear to have had about equally high production rates: mallard, black duck, shoveler, ring-necked duck, and canvasback. The baldpate and green- winged teal seem to have been intermedi- ate in production. The gadwall, pintail, blue-winged teal, redhead, and lesser scaup appear to have had production rates lower than those of the other species. ( Page 466. ) 39. Age ratios obtained through inspec- tion of ducks in hunters' bags were found to be of value in establishing hunting reg- ulations, for they provide a basis for evalu- ating the well-being of the population and the extent to which production may be ex- pected to replace annual losses. (Pages 466-7.) 40. Further progress in waterfowl pop- ulation management, the study concluded, requires a more concerted elifort to obtain age ratio data by design and to relate these data to conditions on the breeding grounds. (Page 467.) LITERATURE CITED Anonymous 1957. Check-list of North American birds. Fifth edition. American Ornithologists' Union, Baltimore, Maryland. 691 pp. Allen, Durward L. 1943. Michigan fox squirrel management. Mich. Dept. Cons. Game Div. 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Kartashev 1958. Wildfowl research in Russia; biological foundations for the regulation of wild- fowling in the central districts of the European part of the U.S.S.R. Pp. 157-69 in Ninth Annual Report of the Wildfowl Trust, 1956-1957. Country Life, Ltd., London. 239 pp. Ticehurst, Claud B. 1938. On a character of immaturity in the Anatidae. Ibis, fourteenth series, 2(4):772-3. Van Den Akker, John B., and Vanez T. Wilson 1951. Public hunting on the Bear River Migratory Bird Refuge, Utah. Jour. Wildlife Mgt. 15(4):367-81. Weller, Milton W. 1957. Growth, weights, and plumages of the redhead, Aythya americana. Wilson Bui. 69(l):5-38. Williams, C. S. 1953. 1953 status report of waterfowl. U. S. Fish and Wildlife Serv. Spec. Sci. Rep.— Wildlife 22. 64 pp. Yocom, Charles F. 1949. A study of sex ratios of mallards in the state of Washington. Condor 51(5):222-7. INDEX The following index covers Articles 1, 2, 3, 4, 5, and 6 of Volume 27 of the Illinois Natural History Survey Bulletin. Indexing has been limited for the most part to the names of birds, fish, insects, mammals, and plants mentioned in the articles. In most cases, the singular form of the word has been used in the index, even though the plural form has been used in the text, as mouse for both mice and mouse. Place names have not been indexed. Of necessity, variation occurs in some of the terms. For example, peach in the index may refer to either the fruit or the tree. Abeiia, 151 Abutilon tlieophrasti, 326 Acanthocephala (acanthocephalan), 66, 137 Acarina, 297, 300, 303, 305, 307, 309, 312, 319, 322, 339 Acnida altissima, 294, 298, 302, 304, 314, 323-4, 332-3 ; see also Water-hemp Aeshna, 296, 305 A'lx sponsa, 254, 312, 394; see also Duck, wood Alderfly, 140 Alfalfa, 150-1, 185, 425 Algae, 16, 18, 20-2. 161. 170, 306, 303-10, 325, 355, 357-8, 380, 387 plankton, 355-7 Alisma subcordatum, 325 Alona, 12 Amaranth, green, 326 Amarantlius retroflexus, 326 Amaryllis, 158 Ambloplitcs rupestris, 1; see also Bass, rock Ambrosia artemisiifolia, 321, 325 psilostacliya, 325 trifida, 325 Ammannia coccinea, 327 Amnicola, 296, 299, 320, 338, 340 binneyana, 319 peracuta, 316 Amphibia (amphibian), 134, 136, 297, 339-40 372 Amphipoda (amphipod), 12, 15-6, 18, 24, 27, 52, 296, 299, 305, 340 Anacharis canadensis, 326 Anas acuta, 232, 297, 393 ; see also Duck, pintail (American) carolinensis, 247, 303, 394; see also Duck, green-winged teal cyanoptera, 247; see also Duck, cinnamon teal diazi, 394 discors, 247, 393 ; see also Duck, blue-winged teal fuh'igula, 394 platyrhynclios, 238, 293, 393 ; see also Duck, mallard rubripes, 257, 293, 314, 394; see also Duck, black strepera, 247, 308, 394; see also Duck, gad- wall Anax Junius, 299, 316 Ancylidae, 12 Anguilla rostrata, 5 Animal, 119, 125, 127-8, 132, 134, 144, 161, 180, 197-8 aquatic, 163, 178 domestic, 346 moss, 338 wild, 201 Animal foods [of waterfowl], 292-3, 295-7, 299-303, 305-23, 337-40, 343 Anisoptera, 12, H-6, 18, 20-2, 29, 296, 299, 305, 338 Annelida (annelid), 12, 15, 22 Annuals, 145 Anser albifrons, 247; see also Goose, white- fronted Anseriformes, 191 Ant, 29, 297, 300, 305, 316, 339 Anthomyiidae, 316, 339 Aphid, 100, 112, 118, 121, 132-5, 138-40 corn root, 117 pea, 118, 123 spotted alfalfa, 118, 123 Aphis, 121 Aphodius distinctus, 297, 299, 309, 312, 319; see also Beetle, scarab femoralis, 312, 316 Apidae, 13 Apis meUifera, 13 Apple, 105-10, 130, 151-2 crab, 157 Apple-leaf folder, lesser, 105 Apricot, 107, 151 Arachnida (arachnoid), 137, 297, 300, 303, 305, 307, 309, 316, 319, 322, 339 Araneae, 12, 16, 18, 22, 300, 316, 319 Arbor vitae American, 146 Chinese, 146 Siberian, 146 Aides herodias, 65 Afffia apicalis, 12 Argiopoidea, 300, 322 Armvworm, 114-5, 117, 123 fall, 123-4 Arrenurus, 12 Arrowhead, common, 300, 337 Arthropoda, 296, 299, 303, 305, 307. 309, 312-4, 316, 319-20, 322, 338 Asellus, 12, 15, 296, 299, 305 communis, 15 Ash, 158, 160 mountain, 157 wafer, 151 Aster, 158 Ataenius, 13 A-vena sativa, 327 ; see also Oats Avens, 327 Ayi/iya, 430 affinis, 239, 315, 393; see also Duck, lesser scaup americana, 254, 321, 394; see also Duck, red- head [475] 47b Illinois Natlral History Survey Bulletin Volume 27 Aythya—lontinueJ loUarij, 254. 317. 393; sn- also Duck, ring- necked mania. 233, 323; s,f also Duck, greater scaup valisintria, 238, 320, 394; see also Duck, caiivasback Azalea, 1$8 B Backswiininer, 296, 338 Bacteria, 27, 77, 147, 153, 161 Bagworm, 118 Barlev. 117, 151 Bass. 165. 171-2, 176, 353-6, 362-5, 367, 371-2, 375-7, 379-88 black, 164 largemouth, 5-6, 10-3, 22-3, 28-9, 36. 49, 62, 68-77, 79. 164, 170, 172-8, 345, 353-4, 359- 61, 365-6, 368, 370-1, 374, 376, 378-82, 384, 387 rock, 1, 43 srnallmouth, 5, 72, 74-6, 79, 175-6, 178 spotted, 5 vcilow, 5 Bean, 152 navy, 326 trailing wild, 326 wild, 326 Beaver. 196 Bedbug. 104. 123 Bee. 29, 121, 135 bumble, 100 Beet, 111 Beetle, 29, 129, 142 asparagus, 105 bark, 118 bean leaf, 118 carpet. 123 Colorado potato, 104-5, 109, 111-2, 115, 123-4 corn flea, 151 cucumber, 111 diving, 296, 299, 303, 305, 307, 309, 312, 314. 316. 319-20, 322, 339 ground, 296, 299, 303, 305, 312, 316, 319-20, 339 Japanese, 104 June, 135, 143 leaf, 135, 297, 300, 305. 307, 313, 319, 339 Mexican bean, 104 rove, 135, 296, 299, 305, 312, 339 scarab, 297, 299, 307, 309, 312, 319, 339 snout. 106. 297, 300, 303, 316, 320, 339 water, 135, 322 water scavenger, 296, 299, 314, 316, 339 whirligig. 296, 303, 305, 312, 319, 339 Beggar-tick, 325 Begonia. 158 Belostoma. 13 Belostomatidae ion some pages misspelled Belastomatidae), 13, 296, 299, 319, 338 Benarus, 319 Berosus, 13 Bidens frondosa, 325 Billbug. 117 Birch. 118 Bird, 86, 96, 105. 120-1, 129-30, 136. 179-81 183-4, 188, 206, 210 tish-eating, 164 game, 181, 183, 199 migratory game, 182 nongame, 182-3 song-, 198 upland game, 182, 186 water, 205 Blackberry, 152 Blackbird, red-winged, 121 Blastobasidac, 144 Blight. 112 Blissus leucopterus, 116-7; see also Bug, chinch Blue jav, 186 Bluegilf. 4-6, 8-10, 39-40, 62, 67-9, 71-2. 74-6, 172-3, 176-8, 345, 353-6, 362-8, 370-88; see also Lepomis macrochirus Bobwhite, see Quail Bonasa umbellus, 467 Bootjack, 337 Borer clover root, 118 elm, 154 European corn, 104, 112, 122-3, 143 flat-headed, 118 flatheaded wood, 296, 339 peach tree, 108 round-headed, 118 squash vine. 111 stalk, 117 tree, 108 Branchiopoda, 305, 338, 340 Branta canadensis, 239, 425 ; see also Goose, Canada Bream, 71 Bruchus granarius, 105 Bryophyte, 161 Bryozoa (bryozoan), 12, 16, 20, 22, 296, 299, 303, 305-8, 312, 316, 319, 322, 338, 340 Bucephala all/cola, 259; see also Duck, bufflehead elangula, 247, 323 ; see also Duck, common goldeneye Buckeye, 158 Buckwheat climbing false. 294, 324 common, 325 Buffalo. 128 Buffalo [fish], 164, 172-3 mongrel, 172 redmouth, 172 Bug, 29, 86, 89, 91, 114 chinch. 93, 114-7, 121, 123-+, 296, 299, 338 plant, 140, 338 squash, 316, 339 stink, 139, 296. 339 water, 296, 299, 319, 338 Bullhead black, 5, 172, 176 yellow, 5 Bulrush alkali, 322, 325 American, 292, 325 green, 325 hard-stem, 309, 318, 325 river, 196, 309, 318, 321, 323, 325, 334, 337, 343 soft-stem, 292, 309, 318, 321, 325 Buprestidae, 13, 296, 339 Bur-reed, 193 1957-1961 giant, 292, 318, 323, 325, 337, 343 Buttercup, 325 Butterriy, imported cabbage, 104 Buttonbush, 292, 294, 298, 300, 302, 304, 306, 311, 313-4, 318, 323-4, 334, 343 Buttonweed, 327 Cabbage, 111, 113 Caddisriy, 15, 21, 23-6, 28, 52, 135, 140, 142, 297, 300, 303, 305, 307, 309, 312, 314, 316, 339-40 Cacnis, 12, 14-5, 27, 29, 299, 305, 338 Calla, 158-9 Calitmorplia Lcconte't, 105 Camallanus oxyceplialus, 65-6, 78 Camharus virilis, 296, 316 Campdoma, 296, 299, 316, 319, 338, 340 CandoTia, 305 Cankerworm, 109, 118, 183 spring, 155 Cajithocamptis, 305 Carabidae, 296, 299, 303, 305, 307, 312, 316, 319-20, 339 Carcx rostrata, 326 Car'inifex, 338 neivbcnyi, 296 Carnation, 158 Carp, 4-5, 164, 172-3, 386 Carpiodes cypriniis, 5 Carpsucker, quiliback, 5 Carrot, 111 Casnonia pennsyl'vanica, 299 Cassia fasciculata, 326 Catalpa, 157, 160 Caterpillar pear, 105 tent, 118 walnut, llo Catfish, 6, 172 channel, 5, 176, 386 flathead, 5 Catostomus commersoni, 5 Cattail, 196 Cattle, 178, 346 Cedar deodar, 146 of Lebanon, 146 red, 146 Celitlicmis, 12 Ccltis occidentalis, 326 ; sec also Hackberry Centrarchidae (centrarchid ) , 1, 65, 70, 78, 171, 178 Ccphalanthus occidentalis, 294, 298, 302, 304, 306, 311, 313-4, 318, 323-4, 334; sec also Buttonbush Ccratophyllum demcrsum, 294, 298, 302, 304, 306, 309, 311, 313-5, 318, 320-1, 323-4, 330; see also Coontail Ceratopogonidae, 13 Cestoda (cestode), 12, 15, 21-2 Chaenobryttus gulosus, 1, 5, 13, 76, 174; see also Warmouth Chaetocncma, 319 pulicaria, 151 Chafers, vine leaf, 183 Cliaoborus, 13, 26 Chara, 355, 358, 376, 387 Charadriiformes, 191 Index 477 Chen caerulescens, 244; see also Goose, blue hypcrborea, 244; see also Goose, snow Chcnopodium album, 325 Cherry, 107, 151-2, 327 Chicken, prairie, 103, 183, 186-7, 198 Chironomidae (chironomid) , 13, 139, 297, 300, 303, 305, 307, 309, 312, 316, 319-20, 322, 339 Chordata, 297, 300, 319-20, 339 Chrysanthemum, 158 Chrysomelidae, 13, 143, 297, 300, 305, 307, 313, 319, 339 Chubsucker, lake, 5 Chufa, 247, 292, 294-5, 298, 302, 304, 311, 318, 323-4, 335, 343 Chydorus, 12 Cicadellidae, 141, 296, 307, 338 Cicadeilinae, 142 Ciliate, 27 Cinquefoil, 326 Cladium mariscoides, 326 Cladocera (cladoceran) , 12, 15-6, 18, 20-2, 24-5, 27-8, 51 Clam, fresh-water, 296, 299, 338 Clanyula /lyemails, 323 ; see also Duck, oldsquaw Clover, 108, 114, 185, 327 sweet, 151 Cloverworm, green, 118 Coccidia, 191 Cockroach, 123 Coenagrionidae, 296, 299, 305 Coleoptera, 13, 16, 18, 20-2, 29, 129, 142, 296, 299, 303, 305, 307, 309, 312-4, 316, 319-20, 322, 339 Coleus, 159 Colinus virginianus, 341 ; sec also Quail Collembola (coUembolan), 12, 15, 20, 22, 144 Colymbetes, 299 Compositae, 326 Coniothyrium, 155 Cojivolvuliis arvensis, 327 Coontail, 193, 269, 294-5, 298, 300-2, 304, 306, 308-11, 313-5, 317-8, 320-4, 327, 330, 343 Coot, 261 Copepoda (copepod), 12, 15-6, 18, 20-2, 25, 27-8, 65, 303, 305, 312, 338 Coralberry, 327 Cord-grass, prairie, 326 Coreidae, 316, 339 Corixa, 296, 299, 303, 305, 307, 309, 312-3, 316, 319-20, 322 Corixidae, 13, 296, 299, 316, 319, 338 Cormorant, 176 Corn, 113-4, 117, 150-1, 160, 177, 192, 195, 199-200, 247-9, 269, 282, 289, 293-5, 298, 300, 304, 306, 308, 311, 313-5, 321, 323-4, 327-8, 343, 348, 350 broom, 151 field, 112 Indian, 204 sweet, 112-3 Cornus, 325 Corydalis cornuta, 296 Cotton, 118 Cottontail, see Rabbit (cottontail) Cottonwood, 148 Cow, 120 478 Illinois Natural History Survey Bulletin Volume 27 Cowbird, 186 Cowpta. 151, 325 frah-grass. 309-10, 326 smooth, 309, 326 Crapp.e. 164. 171, 379 black, 5, 172-3 white. 5. 172-3 Crattudus, 326; see also Hawthorn and Haw Crav.i>"h. 14-5. 21-3, 24-5, 27-30, 51-2, 77, 296, 316, 340 Cricket, 69 Crop, 143, 151, 158 cer.al, 113, 117, 123-4, 160 cu)n()mic, 148, 159-60 field, 149, 352 [fish], 376-7, 379-80, 383 tioricultural. 158-60 torase. 113, 123-4, 148. 160 fruit. 113. 123. 147, 149, 160 Krain. 148. 160 ornamental, 159-60 pasture, 160 vegetable, 113, 147, 160 Crow, 186 Crustacea (crustacean), 130, 133-4, 137, 163, 261. 296. 299, 301, 303, 305-9, 312, 316, 319, 338-40 Cucumber, 151 Culicidae. 13 Curculio. plum, 104, 106-8 Curculionidae, 297, 300, 316, 320, 339 Currant, 151-2 Cuscuta, 327 Cutworm. 115. 117, 123 Cyclops, 12, 305 Cyclorrnapha, 309 Cyperus erythrorhizos, 294, 298. 302, 304, 311, 318, 323—4. 332; see also Nut-grass, red-rooted esculentus. 247, 294. 298, 302, 304, 311, 318. 323-4. 335; see also Chufa ferax. 304, 324 laueastriensis, 153 strigosus, 294. 298, 302, 304, 311, 323-4, 334; see also Nut-grass Cypress (tree), 349 Cyprinus earpio, 5 ; see also Carp eoronarius, 1 Cypris, 305 Cytosporina, 155 D Damselfly, 14-5, 22-6, 28-30, 52, 77. 139. 296, 299, 305, 338 Daphnia, 12 Darter, Johnny, 5, 74 Daunts pusillns, 153 Decapoda (decapod), 12, 14-6, 18, 20-2, 296 Deer, 197-8 red, 129 Deer's tongue, 332 Dendrocygna autumnalis, 394 b'uolor, 394 Deutzia, 151 Dewberry, northern, 327 Diahrotica, 307 undecimpunciata hov.ardi, 300, 305, 313 Dickcissel, 184 Didiptera brachiata, 153 Dig itaria ischaemum, 309, 326 sanguinalis, 309, 326 ; see also Crab-grass Diodia teres, 327 Diptera (dipteran), 13, 15-6, 18, 20-2, 24-6, 28-30, 51-2, 135, 139-40, 142, 297, 300, 303, 305, 307, 309, 312, 316, 319-20, 322, 339 DobsonHv, 140 Dock, pale, 325 Dodder, 327 Dog domestic, 196 hunting, 199 Dogwood, 313. 325 Dotomedes triton sexptinctatus, 12 Dorosoma cepedianum, 5. 340; see also Shad, gizzard Dotliiorella rjuercina, 156 Dothiorella wilt fungus, 155 Dove, mourning, 194—5, 199 Draeiitlacepliala, 307 Dragoniiv, IS, 22-5, 28-30, 52, 77, 139, 296, 299, 305, 307, 316, 338 Dryopidae, 320, 339 Duck, 111, 177, 191-4, 196, 199, 239, 242-50, 252-73, 275-6, 278-80, 282-3, 284-6, 289- 343, 391-4-70 baldpate, 247, 254, 258-62. 264-6. 282, 284. 291, 293, 306-8, 327, 330, 341-3, 404-7, 410- 4, 416-7, 420-3, 425-8, 438-9, 447-8, 458, 470 black, 193, 242, 257-65, 267-8, 285, 289, 291, 293, 314-5, 340-1, 343, 394, 396-7, 399-401, 406-8, 421, 43 5-7, 447, 466, 470 biack-bellied tree. 394 blue-winged teal, 193-4,247,253-60,264,282, 284, 291, 293, 301-5, 311, 332, 334-5, 337, 341, 343, 393-4, 398, 403-4, 406-7, 412-4, 416-8, 420-2, 425, 427-8, 437-8, 466, 470 bufflehead, 259-61, 284 canvasback. 238, 247, 257, 259-65, 267-9, 282, 285, 291, 293. 320-1, 341, 343, 394, 400, 403-9, 412. 414, 416, 420-1, 426-8, 438, 466, 468, 470 cinnamon teal, 247, 412 common goldeneve, 247, 254, 259-61, 284, 291, 323, 341-3 fulvous tree, 394 gadwall, 247, 254, 258-62, 264-6, 282, 284, 291, 293, 308-10, 327, 330, 341-3, 394, 403-8, 411-3, 416-7, 420-2, 425, 427-30, 438, 448, 458, 466, 468, 470 greater scaup, 238, 246-7, 291, 323, 341, 343 green-winged teal, 241, 247, 253, 258-61, 263-6, 284, 291, 293, 303-6, 311, 331-2, 334-5, 337, 341, 343, 394, 403-9, 411-3, 416, 419-23, 425, 428-9, 438-9, 443, 448, 466, 468, 470 lesser scaup, 239, 241, 254, 256-61, 263-5, 267-9, 282, 285, 291. 293, 315-7, 337, 341-3, 393, 402-8, 412-4, 416-7, 419-21, 426-8, 438, 447, 466, 470 mallard, 191-4. 196, 236-50, 254-62, 264-86, 289. 291-7, 300-3, 307, 313, 315, 327-8, 330-1, 333, 335, 340-3, 393-401, 403-70 merganser, 259-61, 284 Mexican, 394 1957-1961 Index 479 mottled, 394 oldsquaw, 291, 323, 341, 343 pintail (American), 196, 238-41, 244, 247, 253-62, 264-9, 281-2, 284-5, 291, 293, 297- 303, 307-8, 327-8, 331-2, 333-5, 337, 341-3, 393, 402-23, 425-9, 438-9, 442-4, 447-8, 454-6, 462-3, 466, 468-70 redhead, 241, 254, 257-69, 282, 285, 291, 293, 321-2, 327, 341-3, 394, 400, 402-4, 406-G, 410-4, 416, 421, 426-8, 438-9, 447, 466, 468, 470 ring-necked, 254, 259-61, 263-5, 267-9, 282, 285, 291, 293, 317-9, 327, 330, 337, 341-3, 393, 405-8, 412-4, 427-9, 466, 468, 470 ruddy, 247, 259-60, 284, 291, 322, 341, 343, 408, 414, 420, 427-8 shoveler, 244-5. 247, 253, 258-61, 263-5, 282, 284, 291, 293, 310-2, 332, 337, 341-3, 394, 403, 406-14, 416, 421-2, 425-8, 437-9, 443, 448, 466, 470 teal, 308, 333, 342 wood, 103, 192, 196, 254-6, 259-61, 264, 282, 234, 291, 293, 312-4, 327, 341, 343, 394, 402-3, 405, 466 Duck-potato, 193, 292, 294-5, 298, 300, 304, 306, 318, 320-1, 323-4, 336-7, 343 Duckweed, 300, 308, 310 lesser, 298, 302, 304-6, 324 Dytiscidae, 13, 296, 299, 305, 307, 309, 312, 314, 316, 319-20, 322, 339 E Earthworm, 69, 133, 137, 356 Earworm, corn, 111—3 Ecliinocliloa a-usgalli, 294, 298, 302, 304, 309, 311, 313-4, 321, 323-4, 330-1 ; see also Millet, wild frumcntacea, 330; see also Millet, Japanese ^valteri, 294, 298, 302, 304, 311, 323-4, 335; see also Millet, Walter's Ectoparasite, 132, 197 Eel, American, 5 Egg plant. 111 Elateridae, 13 Elderberry, 117 Eleocharis obtusa, 325 palustris, 325 parvilla, 325 Elk, 128 Elm, 118, 154-60 American, 155-6 Asiatic, 155 Chinese, 157 English, 157 slippery, 157 Elmidae,"297, 305, 339 Enallagma basidens, 12 carunculatum, 12 civile, 12 signatum, 12 Entomostraca, 29-30, 65 Ephemeroptera, 12, 14-6, 18, 20-2, 141, 296, 299, 303, 305, 307, 312, 314, 316, 319-20, 322, 338 Epicordulia princeps, 12 Eragrostis hypnoides, 298, 302, 304, 311, 323^, 337; see also Grass, teal Erichloa villosa, 153 Erimyzon sucetta, 5 Eristalis, 13 Erythemis simplicicollis, 12 Esox vermiculatus, 5 Etheostoma nigrum, 5, 74 Evergreen, 146 Fagopyrum sagittatum, 325 Field-bindweed, 327 Fir balsam, 146 silver, 146 Fish, 1-79, 96, 103, 129-31, 134-6, 163-4, 166-78, 206, 210, 261, 297, 300-1, 319, 339-40, 342, 345, 350, 353, 355-6, 363-5, 367-8, 372, 375-7, 379-81, 384, 386-8 white, 170 Flagellate, 27 Flea, 104 water, 340 Flower, 146 wild, 153, 206 Fluke, strigeid, 65 ; see also Posthodiplostomum minimum Flumnicola, 296, 316, 319-20, 338 Flv, 119-20, 139, 339, 356 black, 119 buffalo, 119 Hower, 135 hessian, 104, 114-5, 117, 122 horn, 120 horse, 119-20, 297, 339 house, 119-20 ichneumon, 300, 305, 319 lace-winged, 121 stable, 120, 123 Syrphus, 121 Tachinid, 123 two-winged, 111 Fog-fruit, 325 Folder, lesser apple-leaf, 105 Formicidae, 13, 297, 300, 305, 316, 339 Fowl, domestic. 111 Fox, red, 196 Foxtail green, 326 yellow, 326 Frog, 297, 339-40 Fruit, 106-10, 113, 123, 148, 151, 261 grain, 146 Fulica americana, 261 Fundulus diaplianus, 5 notatiis, 5 Fungus (fungi), 121, 147-9, 151-3, 156-7, 160-2, 170-1 bracket, 161 Dothiorella wilt, 155 Galliformes, 191 Gammarid, 319 Gammarus, 296, 299, 305 fasciatus, 319 Gar, short-nosed, 176 Gardenia, 158 Gastropoda (gastropod), 12, 16, 18, 20-2, 26, 480 Illinois Natural History Survey Bulletin Volume 27 Gastropoda (gastropod) — continued 296. 299. 303, 305, 307, 312, 316, 319-20. 338 GfotruPfs, 307 Clfranium, 158 CJerlura, 158 tJcrridac. 13,296, 316, 338 G err is, 13 re mil/is, 316 Grum, 327 Clladiolus, 158-60, 162 Ciogglc-eye, 1 Cicddenrain (tree), 157 Cioldfish, 173 Gurnp/tus notatns, 296 Goose. 238, 259-60, 428, 431 American brant, 260 blue, 241, 244, 246-7, 259-60, 282, 284 Canada. 190-1, 239-40, 243, 246-7, 257-60, 2S4, 425,428.431 lesser snow. 244 snow. 241, 246-7, 259-60, 2C2, 284 white-fronted, 247. 260 Gooseberry, 152 ornamental. 151 Goshawk, 186 Grackie, 186 CJrain, 123. 149 small. 117, 150, 160 Gramineae, 326 Grape, 107, 152 frost, 313, 326 Grass, 115. 117, 146, 188 barnyard, 295, 331 corn, 335 eel, 336 Hungarian, 114 old-witch, 326 prairie, 113, 117 teal, 298, 300, 302, 304-5, 311, 323-4, 336-7, 343 wild, 117 Grasshopper, 69, 105, 114-5, 117, 121, 123, 299, 305, 313 Grouse, ruffed. 467 Grub. 69 white. 114, 117, 121, 159, 162 Gyranlus, 338 parvus, 12, 299, 303. 305. 307, 312, 316 Gyrinidae, 296, 305, 312, 319, 339 H Hackberry, 160, 326 Haliplidae. 13, 296, 299, 339 Haliplus, 13 Haplopappus ciliatus, 153 Haw, 107; srr also Hawthorn and Crataegus Hawk, 186 Cooper's, 186 duck, 186 pigeon, 186 sharp-shinned, 186 Hawthorn, 157-8, 326; see also Haw Hay. 425 llelianlhus angustifalius, 153 Hrliotropium tenrllum, 153 Helisoma, 338 Irivolvis, 296. 299 Hellgrammite, 296, 338 Helminth, 191 Urmerohius, 121 Hemiptera, 13, 16, 18, 21-2, 29, 296, 299, 303, 305, 307, 309, 312-3, 316, 319-20, 322, 33o Heron, great blue, 65 Herring, 36 Heteranthera dubia, 309, 325 ; see also Mud- plantain Ucxagenia, 296, 299, 303, 305, 307, 312, 314, 316. 319-20, 322, 338, 340 limhaia, 12, 14 Hibiscus militaris, 326 Hog, 107-8 Hollyhock, 158 Hom'optera, 13, 22. 296, 307, 338 Honeysuckle, bush, 151 Hornwort, 330 Horse, 119-20 Horsechestiiut, 158 Hyalella azteca, 12 Hydracarina, 300, 303, 305, 307, 309, 312, 319. 322 Hydrachnellae {on one page misspelled Hy- drochnellae), 12, 18, 20, 22 Hydrangea, 158 Hydrophihdae, 13, 296, 299, 307, 314, 316, 339 Hydro porus, 13 Hydropsyclie, 297, 300 Hydropsychidae, 142, 297, 300, 339 HvdroptUidae, 13, 15, 142, 297, 300, 303, 305, 309, 312, 316, 339 Hymenoptera, 13, 16, 18, 21-2, 29, 144, 297, 300, 305, 316, 319, 339 I Ichneumonidae (ichneumon), 300, 305, 319, 339 Ictalurus mclas, 5 ; see also Bullhead, black natalis, 5 ; sec also Bullhead, yellow punctatus, 5 ; sec also Catfish, channel lUinobdella moorei, 66, 78 Ilybius, 13 Insect {sec also Insecta), 51, 89, 91, 102, 104-7, 109, 112-4, 117-25, 129-30, 132, 134-5, 137-8, 139-40, 143, 210, 261, 319 aquatic, 163 scale, 108. 118 Insecta {see also Insect), 296, 299, 303, 305, 307, 309, 312-4, 316, 319-20, 322, 338, 340 Ipomca hcderacea, 326 Iris, 151, 158 Ischnura Posita, 12 vcrticalis, 12 Isopoda (isopod), 12, 15-6, 18, 20-2, 25, 28. 296, 299, 305 Ivy, 158 poison, 326 Juncus, 304, 325 Juniper, 118, 157 Irish, 146 savin, 146 Swedish. 146 Jussiaea leptocarpa, 153 Killifish, banded. 5 K 1957-1961 Index 481 Kinglets, 183 Knotweed, prostrate, 324 Labidestfies sicculus, 5 Ladybug, 121 Lady's thumb, 294, 298, 304, 324 water, 294, 298, 324 Lamb's-quarters, 325 Lamprey, 177 Leafhopper, 123, 135, 141-2, 296, 307, 338 potato, 112 Leafworm, cotton, 104 Leech, 66, 78, 137, 163 Leersia oryzoides, 294, 298, 302, 304, 306, 309, 313-4, 323-4, 328; see also Rice cut-grass Leguminosae (legumes), 118, 326 Lemna minor, 298, 302, 304, 306, 324; see also Duckweed, lesser Lepidoptera, 135, 143, 297, 309, 322, 339 Lepomis, 67 cyancllus, 5 ; see also Sunfish, green gibbosus, 5 ; see also Pumpkinseed htimilis, 5 macrochirus, 5, 13, 178, 345; see also Bluegill megalotis, 5 ; see also Sunfish, longear microlophus, 177; see also Sunfish, redear Leptorhynchoides thecatus, 66 Lespedeza, 151 Leucorrhinia, 12 Libetlula pulchella, 12 Lichens, 146, 161 Lily, 151, 158 water, 146 Limnesia fulgida, 12 Linden, 157 Li piax, 338 siibcarinata, 316 subglobosus, 299 Lippia lanceolata, 325 Liverworts, 146, 161 Livestock, 119-20, 123 Lixus, 300 Locust, 105, 114 17-year, 118 Locust [tree], black, 147, 157 Logperch, 5 Lopfiotocarpns (lophotocarpus), 292, 326 Lotus, 313, 334 American, 292, 311, 325 Louse, 123 apple-root plant, 107 bark, 105, 107, 118 melon, 111 plant, 121 Liiperina stipata, 117; see also Cutworm Lycosidae, 12 Lydella stabulans grisrscens, 123 Lygaeidae, 296, 299, 338 Lygacus, 296 kalmii, 299 Lygus, 338 lineolaris, 299, 307 Lymnaeidae, 12 M Macrocentrus ancylivorus, 122 Macropus leucopterus, 117 Madtom, 5 Magdalis armicollis, 154 Maggot, 111 Magnolia, 157 Magpie, 128 Malacostraca, 296, 299, 305, 338, 340 Mallard, see Duck, mallard Mammal, 129, 136, 182, 195-6, 198-9, 206, 210, 283 furbearing (furbearer), 177, 195-6, 199 game, 197 Man, 119, 125 Maple, 148, 157-8 hard, 160 Mareca americana, 247, 307 ; see also Duck, baldpate Mastodon, 129 Mayfly, 14, 22-30, 52, 77, 135, 141-2, 296, 299, 303, 305, 307, 312, 314, 316-7, 319-20, 322, 338, 340 Meadowlark, 179, 183 Medicago arabica, 153 Megaloptera, 13, 140 Melanotus, 13 Membracidae, 13 Mcrgiis, 259 ; see also Duck, merganser Microcaddisfly, 142 Microfilaria, 191 Microlepidoptera, 144 Micropterus dolomieui, 5, 175 ; see also Bass, smallmouth punctulatus, 5 salmoides, 5, 13, 345 ; see also Bass, large- mouth Microvelia, 13 Midge, 28, 139, 297, 300-1, 303, 305-7, 309-10, 312, 316, 319-20, 322-3, 339-40 wheat, 114-5, 122 Millet, 193, 246, 300 German, 326 Japanese, 292, 330 Walter's 292, 294, 298, 302, 304, 311, 323-4, 335-6, 343 wild, 292, 294-5, 298, 302, 304, 309-11, 313-4, 321-4, 330-1, 336, 343 Mimidae, 183 Mink, 195, 198-9, 425 Minnow, 30, 49, 69, 72-4, 76, 172, 175, 356 bluntnose, 5 bullhead, 73 fathead, 5, 74 Minytrema mclanops, 5 Miridae (mirid), 135, 140, 142, 299, 338 Mite, HI, 119, 133, 157 orobatid, 137 water, 297, 300-1, 303, 305, 307, 309, 312, 319, 322, 339-40 Mold, 161 slime, 161 Mole, 195 Mollusca (mollusc, moliusk), 128, 134, 296, 299, 303, 305-9, 312, 314, 316-7, 319-20, 338-40 Morning-glory, ivy-leaved, 326 Mosquito, 27, 119-20, 139 Moss, 146, 161 Moth, 130, 143-4, 309 clothes, 123 codling, 104, lOC-10, 123-4 cutworm, 297 gypsy, 118 482 Illinois Natural History Survey Bulletin Volume 27 Moth — continuid oriental fruit, 104. 108, 122 Mouse. 200 Moxostoma anisut um, 5 (lurrolitm, S Mud-plantain, 309-10, 325 Mulbtrrv, 151 Mule, 119 Muuultum, 338, 3+0 trattsirrsum, 296, 299, 316, 319 Mushroom, 147, 161 Muskrat, 195-6, 198. 342, 463 Mussel, 170, 296-7, 299, 303, 312. 314, 316, 319-20, 338-9, 343 Myriophyllnm luterophyllum, 325 N Naiad northern, 325 southern, 325 Sajas ftexilts. 325 guaJalut>ensis, 325 Nectarine, 107 Sflumho Intea, 311, 325; see also Lotus, Ameri- can Nematode, 65, 150, 161 Seoconocephalus , 299 Seodiprion sertifer, 122 Nepidae, 13, 296, 299, 338 Seritina, 316-7, 338, 340 Nettle, horse. 111 Neuroptera, 13, 16, 20, 22, 296, 338 Nightshade, 326 Noctuidae, 297 Sotemigonus crysoleucas, 5 ; see also Shiner, golden Noloriecta, 296 Notonectidae, 13, 296, 338 Sotrnpis 'volucellus volucellus, 30 Soturus, 5 Nut-grass, 193, 294, 298, 300, 302, 304, 311, 324, 334, 343 red-rooted, 294, 298, 302, 304, 311, 318, 323-4, 332, 334, 343 Nymphaea tuherosa, 325 o Oak, 118, 145-6, 156-8, 160 blackjack, 147 pin, 148, 191. 313, 325 white, 325 Oats, 114, 151, 199, 327 Odonata, 12, 14, 29, 139, 296, 299, 305-7, 316, 338, 340 Oecftis clnerasi ens, 13 inconspinta, 13 Oligochaeta, 12 01or huerinalor, 239; see also Swan, trumpeter folumhianus, 238; see also Swan, whistling Omophron. 307, 339 Onion, 111 Orange, osage, 183 Orchid, 158 Orconertes propinquus propinquus, 12 liriits, 12 Organism, 171, 200 animal, 261 aquatic, 163, 169, 178 Orthopt.-ra, 94, 133, 137, 299, 305, 313, 338 Orthorrhapha, 309 Orthotrichia, 13 Ostrocoda (ostracod), 12, 15-6, 18, 20-1, 25-7, 30, 296, 299, 303, 305, 309, 312, 338, 340 Owl, 186 great horned, 186 Oxyrt/iira, 13 ijxyura jamaiccnsis, 247, 322 ; see also Duck, ruddy Pacliydiplax longipcnnis, 12 Paddlehsh, 174 Palaemonctes paludosa, 30 Panic-grass, fall, 302, 326 Panicum capiltare, 326 d'uhotomiflorum, 302, 326 Parasite, 144, 149, 187, 189, 191 blood, 195 helminth, 188, 191, 195 oriental fruit moth, 122 Parsnip, 111 Partridge-pea, 326 Paspalum, ciliate-leaved, 326 Paspalum ciliatifolium, 326 Pea, 152 sweet, 158-9 Peach, 106-8, 122, 149, 151-2 Pear, 106, 108, 147, 151-2 Pecan, 151, 191 Pect'niaiella, 340 Pcleiypoda, 296, 299, 303, 305, 312, 314, 316, 319-20, 338 Peltodytes, 13, 29 Pentatomidae, 296, 339 Pentatomoidea, 139 Peony, 158-9 Peperomia, 158-9 Pepper, 151-2, 161 Perca fiavescens, 5 Perch, yellow, 5 Percina caprodes, 5 Pcritlicmis tenera, 12 Periwinkle, 158 Petunia, 158 Phalangid, 134, 137 Phaseolus, 326 Pliasianus colchicus, 425 ; see also Pheasant Pheasant, 187-8, 190, 198, 425 ring-necked, 189-90, 341, 464 Phoma, 155 Phryganeidae {on one page misspelled Phyr- ganeidae), 13, 15 P/iyllop/iaga futilis, 13, 143 Phyllotreta, 13 Physa, 65, 296, 307, 319, 338 gyrina, 12, 299, 305 Integra, 12 Physidae, 12 Phytolacca americana, 327 Pickerel, grass, 5 Pickerelweed, 292 heart-shaped, 326 1957-1961 Index 483 Pigeon, wild, 128 Pigweed, 332-3 Pike northern, 164 wall-eyed, 170 Pillbug, 340 Pimephales notatus, 5 promclas, 5, 74 vigilax, 73 Pine, 157, 161, 349 Araucarian, 146 Austrian, 146 Himalayan, 146 red, 160 Scotch, 146 white, 146, 160 Pintail, see Duck, pintail (American) Pisauridae, 12 Pisces, 13-6, 18, 21-2, 297, 300, 319-20, 339-40 Pisidiiim, 296, 299, 303, 312, 316, 319, 338, 340 Plankton, 137, 147, 166-71, 184 Planorbidae, 12 PlaTiorbis, 296, 299, 338 Plant, 129, 145-7, 151-4, 159-63, 178, 210, 261, 343 aquatic, 166, 193, 261, 358 crop, 147, 149 drug, 154 evergreen, 146 floricultural, 158 marsh, 193 moist-soil, 193, 300-1, 308, 310, 318, 327, 331-2, 337, 343 ornamental, 118-9, 148-9, 158, 162 wild, 195, 329, 343 Plant disease collection, 152 Plant disease survey, 149 Plant foods [of waterfowl], 154, 193, 292-5, 298, 300-15, 317-37, 343 Plant-louse, cabbage. 111 Plathcmis lydia, 13 Plecoptera, 139-40, 142 Pleurocera, 296, 316, 319, 338, 340 Plum, 106-7, 152 PlumateHa, 12, 340 Podura aqiiatica, 12 Poinsettia, 158 Pokeweed, common, 327 Polygonum amphibium, 294, 298, 324 aviculare, 324 coccineiim, 294, 298, 302, 304, 306, 309, 311. 313-4, 318, 321, 323-4, 329; see also Smart- weed, marsh hydro piper, 294, 298, 304, 318, 324 hydroptperoides, 294, 298, 306, 313, 324; see also Smartweed, swamp lapathifoliinn, 294, 298, 302, 304, 306, 309, 311, 318, 321, 323-4, 333; see also Smart- weed, nodding pensylvanicum, 294, 298, 302, 304, 306, 309, 311, 318, 321, 323-4, 334; see also Smart- weed, large-seeded persicaria, 294, 298, 304, 324 punctattim, 294, 298, 302, 304, 306, 311, 318, 321, 324 sagittatum, 294; see also Tearthumb, arrow- leaved scandens, 294, 324 Polyodon spathula, 174 Pondweed, 193, 306, 317 horned, 326 large-leaved, 294, 324 leafy, 294, 298, 304, 306, 315, 318, 320, 322, 324 longleaf, 294, 298, 300, 302, 304, 306, 309-11, 313-5, 318, 320-4, 331-2, 343 ribbon-leaf, 302, 304, 324 sago, 294, 298, 301-2, 304, 306, 311, 313-5, 318, 320-1, 323-4, 336, 343 small, 294, 298, 304, 314-5, 318, 320, 324 thoroughwort, 294, 324 white-stem, 294, 318, 324 variable-leaf, 318, 324 Pomoxis annularis, 5 ; see also Crappie, white nigromaculatus, 5; see also Crappie, black Pontederia cordata, 326 Poplar, 157 Portulaca, 327 Posthodiploslomum minimum, 65-6, 78 Potamogeton, 358 amplifalius, 294, 324 cpihydrus, 302, 304, 324 foliosus, 72, 294, 298, 304, 306, 315, 318, 320, 324; see also Pondweed, leafy gramineus, 318, 324 nodosus, 294, 298, 302, 304, 306, 309, 311, 313-5, 318, 320-1, 323-4, 331-2,; see also Pondweed, longleaf pectinatus, 294, 298, 302, 304, 306, 311, 313-5, 318, 320-1, 323-4, 336; see also Pondweed, sago perfoliatus, 294, 324 praelongus, 294, 318, 324 pusillus, 294, 298, 304, 314-5, 318, 320, 324 Potato Irish, 111-2, 123, 152 wild, 111 Potentilla, 326 Poultry, 112, 119 Probythinelta binneyana, 316, 319 Procambarus blandingii acutus, 12 Proteocephalidae, 12 Proteocephalus ambloplites, 65-6, 78 Protozoa (protozoan), 27, 77, 122, 134, 137, 163, 166, 191 Prunus, 327 ; see also Plum americana, 107 domestica, 107 Pseudoscorpion, 134, 137 Psocid, 135 Pumpkinseed, 5, 10, 39, 62 Purslane, 327 Pylodictis olivaris, 5 Q Quail, 188-9, 198 bobwhite, 187-8, 199, 341 Quere us alba, 325 palustris, 313, 325 ; see also Oak, pin Quince, 108 Japanese, 160 484 Illinois Natural History Survey Bulletin Volume 27 R Rabbit (cottontail), 197-9 Raccoon, IVJ, 196, 425 RaKwccil loininon, 321, 32S ^iant, 117 great, 325 western, j25 Ranatra. 13, 296,299 Rtinuniulus, 325 Raspberry, 152 Kai. Nj)rwav, 104 Re.l top. 151 Redbuil, 157 Reiihorse nt>rthern, 5 silver, 5 Redtop (marsh smartweed), 329 Reptile, 103, 134, 136,210 Rhiiijovelia, 13 Rhajihidophorinae, 313 Rliizuiloiiium, 357 Rhubarb, 151 Rhus ij',:ihra, 326 nuiicans, 326 Rice, 178, 239 Rice cut-grass, 193, 294-5, 298, 300, 302, 304, 306, 309-10, 313-4, 323-4, 328, 343 Rocius mississippiensis, 5 Rosa, 327 Rose, 158-9, 327 multiflora, 157, 188 Rose-mallow, scarlet, 326 Rotifer, 137, 163, 166 Ruhus flaycUaris, 327 Rudheckia missouricnsis, 153 Rum ex acetosclla, 325 altissimus, 325 Rush, bog, 304, 325 Rye, 1 14, 348 Sagiltaria cunrata, 294, 324; see also Wapato lalifolia. 294, 298, 304, 306, 318, 320, 323-4, 336-7; sec also Duck-potato Salix. 325 Saperda tridcntata, 154 Saw-fly, 135, 144 currant, 105 pine, 122 Saw-grass, 328 Scale, San Jose, 97, 104, 109-11 Scarabaeidae, 13, 297, 299, 307, 309, 312, 316, 319, 339 Sfirpus acutus. 309, 318, 325 americanus, 325 ; sec also Bulrush, American alroi'irens, 325 flui'iatilis, 309, 318, 321, 323, 325, 337; see also Bulrush, river paludosus, 325 ; see also Bulrush, alkali ^•alidus, 309, 318, 321, 325; see also Bulrush, soft-stem Screwworm, 123 Scud, 30 Sedge, beaked, 326 Setaria faberii, 153 glauca, 326 ilatiia, 326 viridis, 326 Shad, giz/ard, 4-6, 172-3, 340 Sheep, 109 Shiner golden, 5, 173, 176 northern mimic, 30 Shrimp, 30 fairy, 305 Shrub, 104, 145, 153, 157, 159-60, 206 Sialidae, 13 Stalls, 13 Sida, prickly, 326 Sida spinosa, 326 SiUerside, brook, 5 Simnceplialus, 12, 28 Simutium, 119 Siphlonurus, 12, 14, 26-9 Sisyridae, 13 Skunk, 424 Smartweed, 193, 246 dotted, 294, 298, 302, 304, 306, 311, 318, 321, 324 large-seeded, 292, 294, 298, 302, 304, 306, 309, 311, 318, 321, 323-4, 333, 334, 343 marsh, 292, 294-5, 298, 300, 302, 304-6, 309- 11, 313-4, 318, 321, 323-4, 329-30, 334, 343 nodding, 292, 294, 298, 300, 302, 304, 306, 309, 311, 318, 321, 323-4, 333, 343 Pennsylvania, 334; see also Smartweed, large-seeded swamp, 292 ; see also Polygonum hydropiper- oides or Water-pepper, mild Snail, 25, 27, 30, 65, 296-7, 299, 303, 305-7, 312, 316-7, 319-20, 323, 338-9, 343 fresh-water, 340 land, 137, 206 water, 317 Snapdragon, 158 Snout-beetle, reddish elm, 154 Solatium, 326 Somatogyrus, 338 suhglosus, 316, 319 Sorghum, 114, 327 Sortflium vuh/are, 327 Sorrel, Held, 325 Soybean, 151 Sparganium eurycarpum, 318, 323, 325, 337; see also Bur-reed, giant Sparrow, English, 183 Spartitia pcctinata, 326 Spatula clypcata, 247, 310, 394; see also Duck, shoveler Spccularia hiflora, 153 Sphaeriidae, 296, 299, 316, 319, 338 Spharrium, 296, 299, 303, 305, 319-20, 338, 340 stamiucum, 316 Spider, 300, 316, 319, 322, 340 Spike-rush blunt, 325 common, 325 dwarf, 325 Spindleworm, 117 Spittlebug, 123 Springtail, 135, 144 Spruce, 157 1957-1961 Index 485 black, 146 Douglas, 146 Norway, 146, 160 red, 146 Squash, 151 Squirrel, 157 fox, 192, 197-8,425,467 gray, 197 Stagnicola, 296, 319, 338 Staphylinidae, 296, 299, 305, 312, 339 Stevia, 158 Stock, 158 Stonefly, 100, 135, 139-40, 142 Stratiomyidae, 13 Strawberry, 107, 114, 152 Strophostyles hclvola, 326 Sucker spotted, 5 white, 5 Sumac fragrant, 151, 160 smooth, 326 Sunfish, 1, 7, 15, 30, 39, 42, 48-9, 67, 74 green, 5, 47, 67-8, 74, 178, 354 longear, 5, 62 orangespotted, 5 redear, 74-5, 176-8 Sunflower, 118 Swan, 191 trumpeter, 239, 245, 247 whistling, 238-41, 243-6, 284 Swine, 109, 178 Sycamore, 148, 157-8 Sympctriim obtriisum, 13 Symplioricarpos orbiculalus, 327 Syrphidae, 13 Tabanidae (tabanid), 13, 120, 123, 297, 320, 339 Tabanus, 119-20, 320 Tadpole, 30 Tamarack, 161 Tapeworm, 39, 187 bass, 65 ; see also Proteocephalus ambloplites Tearthumb, arrow-leaved, 294, 324 Tetragoneuria, 13 Tettigoniidae, 305 Thistle, Canada, 147 Thrips, 135, 143 Thvsanoptera, 143 Tick, 119, 123, 133-4-, 197 Timothy, 114, 117, 151 Tiphia, 297, 300, 339 Tiphiidae, 297, 300, 339 Tomato, 152 Tooth-cup, 327 Topminnow, blackstripe, 5 Torfrix mallvorana, 105 Tree, 104, 107, 118-9, 149, 153-5, 157, 159-60, 188, 191, 206; see also individual speeies forest, 147-8, 154 roadside, 147 shade, 154 street, 147 Trichoptera, 13-6, 18, 20-2, 142, 297, 300, 305, 307, 309, 312, 314, 316, 319, 322, 339 Trifolium, 111 Triticum aestivum, 294, 324; see also Wheat Tropisternus, 13 Trout, 170, 357 salmon, 170 Tubercularia itlmi, 15 5 Tuberose, 158 Tubuiifera, 143 Tulip, 158 Tupelo, 157 Turdidae, 183 Turkey, 111-12 Turnip, 111 Twig-rush, 326 U Ulmus parvifolia, 155 pumila, 155 Ulothrix zonata, 306 Unionidae, 296, 299, 338 V Vegetable, 106, 111, 113, 123, 148 Veliidae, 13 Velvet-leaf, 326 I'erbascum virgattim, 153 I'erbena hastata, 326 Vervain, blue, 326 Vigna sinensis, 325 ; see also Cowpea Vine, 146 Violet, 158-9 African, 158 I'itis cordifolia, 313, 326 Viviparus, 338 mviparus, 316, 319 W VS^alleye, 164 Walnut, 158 Wapato, 294, 324, 337 Warbler, prothonotary, 186 Warmouth, 1-79, 174-6, 178 Wasp, tiphiid, 297, 339 Water boatman, 296, 299, 303, 305-10, 312-3, 316, 319-20, 322, 338, 340 Water strider, 296, 316, 338 Waterfowl, 191-4, 196, 198, 235-86, 289, 291, 332-3, 335, 340, 391-5, 422-4, 427-8, 430, 447-9, 456, 458, 462-70 Water-hemp, 292, 294, 298, 300, 302, 304, 306, 314, 323-4, 332-3, 343 Water-lily, yellow, 325 Watermelon, 151 Water-milfoil, 325 Water-pepper. 294, 298, 304, 318, 324 mild, 294, 298, 306, 313, 324; see also Smart- weed, swamp Water-plantain, 325 Waterscorpion. 296, 299, 338 Waterweed, 326 Wayfaring [tree], 157 Webworm burrowing, 117 sod, 117 Weeds, 145, 154, 188, 358 Weevil, 135 clover leaf, 118 red elm bark, 154 sweet clover, 118, 123 486 Illinois Natural History Survey Bulletin Volume 27 Wheat. 113-5, 117, 122. 149-51. 178. 294, 324, Y 348 350 Yellow-wood, 157 Willow.' 157. 325 Yew Wireworm. 117-8 English, 146 Wood duck, sff Duck, wood Irish, 146 Woodchuck, 199 Worm, 68. 3 56 . . . ^ apple 104 107-9 Zantnchelha palustrts, 326 aquatic, 166 Zca mays, 294, 298, 304, 306, 311, 313-4, 321, cabbage. 113 323-4. 327 ; j<'/' a/jo Corn catalpa, 356 Zinnia, 158 joint, 114 Zygoptera, 12, 14-6, IS, 20-2, 29, 296, 299, 305, parasitic, 297, 339 338 I Some Publications of the Illinois Natural History Survey BULLETIN Voiuise 26, Article 4.—Efficiency and Selec- tivity of Commercial Fishing Devices Used on the Mississippi River. By William C. Starrett and Paul G. Barnickol. July, 1955. 42 pp., frontis., 17 figs., bibliog. Volume 26, Article 5.—Hill Prairies of Illi- nois. By Robert A. Evers. August, 1955. 80 pp., frontis., 28 figs., bibliog. Volume 26, Article 6.—Fusarium Disease of Gladiolus: Its Causal Agent By Junius L. Forsberg. September, 1955. 57 pp., frontis., 22 figs., bibliog. Volume 27, Article 1.—Ecological Life History of the Warmouth. By R. Weldon Larimore. August, 1957. 84 pp., color frontis., 27 figs., bibliog. Volume 27, Article 2.—A Century of Biological Research. By Harlow? B. Mills, George C. Decker, Herbert H. Ross, J. Cedric Carter, George W. Bennett, Thomas G. Scott, James S. Ayars, Ruth R. Warrick, and Bessie B. East. December, 1958. 150 pp., 2 frontis., illus., bibliog. $1.00. Volume 27, Article 3.—Lead Poisoning as a Mortality Factor in Waterfowl Populations. By Frank C. Belirose. May, 1959. 54 pp., frontis., 9 figs., bibliog. 50 cents. Volume 27, Article 4.—Food Habits of Migra- tory Ducks in Illinois. By Harry G. Ander- son. August, 1959. 56 pp., frontis., 18 figs., bibliog. 50 cents. Volume 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. CIRCULAR 46.—Illinois Trees: Their Diseases. By J. Ced- ric Carter. April, 1961. (Second printing, with alterations.) 99 pp., frontis., 93 figs. Single copies free to Illinois residents; 25 cents to others. 48.—Diseases of Wheat, Oats, Barley, and Rye. By G. H. Boewe. June, 1960. 159 pp., frontis., 56 figs. Single copies free to Illinois resi- dents; 25 cents to others. BIOLOGICAL NOTES 33.—A New Technique in Control of the House Fly. By Willis N. Bruce. December, 1953. 8 pp., 5 figs. 34.—White-Tailed Deer Populations in Illi- nois. By Lysle R. Pietsch. June, 1954. 24 pp., 17 figs., bibliog. 35.—An Evaluation of the Red Fox. By Thomas G. Scott. July, 1955. (Second printing.) 16 pp., illus., bibliog. 36.—A Spectacular Waterfowl Migration Through Central North America. By Frank C. Belirose. April, 1957. 24 pp., 9 figs., bibliog. 37.—Continuous Mass Rearing of the Euro- pean Corn Borer in the Laboratory. By Paul Surany. May, 1957. 12 pp., 7 figs., bibliog. 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- liog. 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. MANUAL 4.—Fieldbook of Illinois Mammals. By Donald F. Hoffmeister 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 Illinois Natural History Survey publicarions 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 Chief, 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 ¥