Bulletin STATE OF ILLINOIS DwiGHT H. Green, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Frank G. Thompson, Director NATURAL HISTORY SURVEY DIVISION Theodore H. Prison, Chief \'olume 23 BULLETIN Article 5 Fox Squirrels and Gray Squirrels In Illinois LOULS G. BROWN LEE E. YEAGER Printed by Authority of the State of Illinois URBAN A, ILLINOIS September 1945 STATE OF ILLINOIS DwiGHT H. Green, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Frank G. Thompson, Director BOARD OF NATURAL RESOURCES AND CONSERVATION Frank G. Thompson, Chairman William Trelease, D.Sc, LL.D., Biology* Arthur Cutts Willard, D.Eng., LL.D., Ezra J. Kraus, Ph.D., D.Sc, Forestry President of the University of Illinois L. R. HowsoN, B.S.C.E., C.E., Engineering Norman L. Bowen, Ph.D., Geology Roger Adams, Ph.D., D.Sc, Chemistry NATURAL HISTORY SURVEY DIVISION Urbana, Illinois Scientific .\nd Technical Staff Theodore H. Prison, Ph.D., Chief Florence A. Nyberg, Assistant to the Chief Section of Economic Entomology G. C. Decker, Ph.D., Entomolgist M. D. Farrar, Ph.D., Research Entomolo- gist J. H. Bigger, M.S., Associate Entomologist S. C. Chandler, B.S., Southern Field Ento- mologist James W. Apple, M.S., Northern Field Entomologist (on leave) B. G. Berger, M.A., Assistant Entomologist John M. Wright, B.A., Assistant Ento- mologist (on leave) H. B. Petty^ Jr., M.A., Associate in Ento- mology Extension C. J. Weinman, Ph.D., Special Research Assistant Willis N. Bruce, B.S., Special Research Assistant Section of Insect Survey H. H. Ross, Ph.D., Systematic Entomologist Carl O. Mohr, Ph.D., Associate Entomolo- gist, Artist (on leave) B. D. Burks, Ph.D., Assistant Entomolo- gist (on leave) Milton W. Sanderson, Ph.D., Assistant Entomologist Phyllis A. Beaver, Laboratory Assistant Section of Forestry James E. Davis, M.F., Extension Forester Section of Aquatic Biology George W. Bennett, Ph.D., Limnologist D. F. Hansen, Ph.D., Assistant Zoologist Paul G. Barnickol, M.A., Ichthyologist Section of Game Research and Managemer R. E. Yeatter, Ph.D., Game Specialist Section of Wildlife Experimental Areas Arthur S. Hawkins, M.S., Game Tech nician (on leave) F. C. Bellrose, Jr., B.S., Associate Gam Technician Harold C. Hanson, M.S., Assistant Gam Technician Section of Applied Botany and Plant Pathology L. R. Tehon, Ph.D., Botanist J. C. Carter, Ph.D., Assistant Botanist G. H. Boevve, M.S., Field Botanist J. L. Forsberg, M.S., Research Pathologist Bessie B. Henderson, M.S., Research Assist ant Section of Publications James S. Ayars, B.S., Technical Editor Eleanor G. Wolff, B.Ed., Assistant Ted nical Editor Technical Library Marguerite Simmons, M.A., M.S., Techn cat Librarian ^ Consultants in Herpetology: Howard K. Gloyd, Ph.D., Director of the Museum, Chicag Academy of Sciences; Clifford H. Pope, B.S., Curator of Amphibians and Reptiles, Chict Natural History Museum •Deceased January 1, 1945. This paper is a contribution from the Section of the Cooperative Wildlife Restoration Program and the Section of Forestry. (84217—3M—6-45) CONTENTS Page Objectives of Project 449 Methods of Study 45O Acknowledgments 453 Populations 454 Distribution 454 Density 455 Species Ratios 455 Sex Ratios 458 Age Classes 45O Species Competition 453 Daily Activity 454 Seasonal Movements 465 Local Movements 466 Migration 466 Dispersal 467 Condition 467 Weight 467 Length. 470 Deformities 470 Wounds 470 Molt and Color 471 Parasites and Diseases 471 Predation 473 Breeding 473 Breeding Seasons 474 Mating Chase 481 Physiological Aspects 481 Testes 48 1 Cowper's Glands 482 Scrotum 482 Oestrus 483 Pregnancy 483 Gestation 484 Mammae 485 Young Rearing 486 Birth Dates 486 Birth Sites 487 Lactation 487 Development of Young 487 Litter Size 489 Illinois Habitats 490 Black Prairie Habitats 490 Woodland Habitats 492 River Bluffs and Bottoms 492 Wooded Upland 493 Miscellaneous Habitats 495 Foods and Feeding 496 Food Sources 497 Food Succession 503 Food Preferences 505 Storing and Feeding Habits 508 Minerals 510 Water 510 Nesting 51 Dens 51| Leaf Nests 5li Hunting 516 Hunters and Hunting Methods 516 Kill 519 Management 520 Habitat Improvement 520 Forestry Practices 520 Hedgerows and Fencero n r- 521 Den Boxes 522 Control of Fire and Grazing 522 Winter Feeding 523 Hunting Seasons 524 Effect of Early Seasons 525 Recommended Seasons 526 Summary 529 Literature Cited 533 n •St Squirrel hunting is highly prized by those who participate in it, both" for its recreational value and because it means "meat on the table." Illinois hunters kill approximately 1,400,000 squirrels annually, of which about 70 per cent are fox squirrels. Fox Squirrels and Gray Squirrels /// Illinois LOUIS G. BROWN LEE E.YEAGER SINCE the passing of big game in Illinois, fox squirrels and gray squirrels have never ranked lower than second among game mammals of this state in importance to hunters. First place is now a toss-up between these tree squirrels and cottontail rabbits, with the latter declining in public esteem because of recent epidemics of tularemia (Yeatter & Thompson 1943), a disease more com- monly associated with rabbits than other game. Despite the long-standing importance of squirrels, very little information has been available upon which to base Illinois hunting regulations, management and res- toration measures relating to them. Laws in regard to hunting seasons have been varied, and at times grossly unsound bi- ologically. The most common problem pertaining to seasons is that of mid- or late-summer hunting. Such hunting is demanded by many hunters, particularly in the southern part of the state. The Illinois squirrel season for the biennium of 1939-41 opened, in this area, on July 15. The date was set back to August 1 in 1941, but again advanced to July 15 in 1943. These early opening dates, as would be expected, resulted in numerous complaints from conservation organizations and from some sportsmen. Lawmakers and admin- istrative personnel, in coping with the situation, were greatly handicapped by the lack of specific information, despite recent investigations in Ohio, Michigan and other states. In particular, information on squirrel breeding was scarce, and it was feared that such as was available was "llliiii.i- F(-i]er;il Aid Hiihllratlr.n No. 4. not fully applicable to Illinois conditions. A season similar to that in Ohio or Mich- igan, considered sound, would retard the opening date in Illinois 2 months or more; and Illinois hunters, to whom summer squirrel shooting is traditional, could be expected to oppose strongly and in good faith such a restriction on their sport. For educational purposes as well as for administrative use, therefore, a fact-finding study was needed in Illinois. The Federal Aid Project on which this report is based was proposed jointly by the Illinois Natural History Surve>- and the Illinois Department of Conservation. Formally known as "Squirrel-Raccoon Investigation and Management in Illinois, Project 14-R," the study was initiated on July 1, 1940, and terminated as a project on June 30, 1942, although some field work, in connection with other projects, was continued through 1944. Early in the investigation it was found that, despite the similarity in some squirrel and raccoon habitats, the two phases of the study could not be carried on adequately at one time by one man ; only the seruor author was available for field work during the greater part of the investigation. Accordingly, the raccoon phase was dropped except for observations that could be made inciden- tally or as a part of regular squirrel studies. OBJECTIVES OF PROJECT The project had two main objectives, as follows: 1. Determination of squirrel breeding seasons and related biology, the informa- tion derived to be used in recommending biologically sound squirrel hunting seasons. [4491 450 Illinois Natural History Survey Bulletin Fol. 23, Art. 5 2. Determination of the environmen- tal requirements of Illinois squirrels, the information on this subject to be used in management and restoration practices. METHODS OF STUDY Illinois, with a north-south length of 385 miles, is subject to greater seasonal variations than any other midwest state. In the formulation and administration of fish and game laws, these variations are partially compensated for through the division of the state into the northern, central and southern zones, fig. 1, each comprising about one-third of the state and each representing a difference in sea- son of 6 or 7 days. The necessity for determining seasonal variations in squirrel breeding and related phenomena in each of the three zones was recognized at the beginning of the project. ILLINOIS WMIieSlOE L t C --r^^— r I BUREAU I jj I L "««s"»i-i. y^ t iKKo.p ^ ii r ' i RANDOLPH PERRY I C L A V - . , I mCHLANO [LAWRENCE/ I 1 "•'"" 11}/, I JEFFERSON I I BE,,. ) -j / ' , / FRANKLIN I ^ j '""" IwilliamsonI saline oallatin;)- UNION IJOHNSONlp O P El Fig. 1.—Map of Illinois showing the three zones on which the game and fish code of the state is based. It appeared, therefore, advisable for the senior author to spend the first 10 days of each month in the southern zone, the sec- ond 10 days in the central zone, and the last 10 days in the northern zone, collect- ing and studying during each period a sufficiently large number of fox and gray squirrels to determine seasonal differences in reproduction. Because such a plan, however sound theoretically, was expensive in travel time, only the first year was given to this periodical study by zones. During this time the zonal differences in the seasons of reproductive activity were determined approximately. The second year was devoted to intensive field study on representative central zone areas, on which both fox and gray squirrels oc- curred. In general, data on breeding and other seasonal phases of this study relate to the central zone, except where otherwise stated, and practical utilization of the information in the northern and southern zones necessitates appropriate allowance in time. Sample material yielding information on squirrel biology consisted of freshly shot, steel-trapped and live-trapped specimens. Study of dead specimens was carried on mainly in several improvised field stations, although some material was examined in Natural History Survey or University of Illinois laboratories. Live-trapped squir- rels were examined in the field, usually at the site of capture. Both fox and gray squirrels were available for study every month for the duration of the project, al- though it was of course impossible to obtain equal numbers of squirrels each month, either in species or sex. Fox squir- rels far exceeded gray squirrels in number, amounting to about 70 per cent of the total examined. Each collecting method has its advan- tages. Over much of the study period guns and steel traps were employed simul- taneously. Hunting was most effective during the main mast-feeding months, from mid or late August into October. Trapping was particularly successful during the winter and early spring, when corn was readily taken as bait. Traps were set, uncovered, on logs and each was baited with a half ear of corn, usually impaled on a nail a few inches above the trap. Twenty-five to 50 traps September, 1945 Brown & Yeager: Squirrels in Illinois 451 were employed, and they were visited at breeding, pregnancy and lactation. Many least daily, and, as often as possible, twice squirrels were taken repeatedly. This daily. The most serious disadvantage of phase of the study supplied information this trapping method was that of taking on species ratio, sex ratio, population den- animals other than squirrels. These in- sity, movements and home range, in addi- ^••»- ^jy.~'^ -^i sft- •IT'** Fig. 2.—Live trap, baited with shelled corn, in a tyjiical set location. Fifty live traps, used in three Pike County areas, yielded useful information on squirrel populations and life history. eluded skunks, foxes, raccoons, opossums, woodchucks, cottontail rabbits and a variety of birds. Since No. 1 traps were used, practically all mammals caught ex- cept squirrels and rabbits were uninjured and were released at the point of capture. Most birds caught in the traps were dead when found. Blue or red corn was found to attract fewer birds than yellow corn, but it appeared to be somewhat less at- tractive to squirrels. Live trapping, which was conducted in three wooded areas in Pike County, in- volved both fox squirrels and gray squir- rels. Shelled corn was used for bait. Fifty live traps of the type described by Baumgartner (1940) were used, fig. 2. Squirrels so taken were not killed, but were examined in the field for evidence of tion to breeding and related data. Vari- ous animals, including woodchucks, cotton- tail rabbits, skunks and opossums, and a few birds, were captured in the live traps. These were unharmed and were released. The period of continuous trapping was from October 16, 1941, to August 7, 1942. Prior to each of the two hunting seasons, 1940 and 1941, covered by this project, copies of a questionnaire were distributed thr(jughout the main squirrel hunting regions of the state. This questionnaire contained blanks to be filled by hunters before the copies were returned to the project leader. It was hoped that from the returned forms information pertaining to kill, distribution, species ratio and population trends could be obtained. A total of 3,300 forms were distributed 452 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 during the 2 years, of which onlj' 236, or 7 per cent, were returned. The writers consider that the most valuable informa- tion yielded by the questionnaire pertained to population trends and hunters' opinions of squirrel seasons. Data pertaining to breeding were ob- tained directly from examination of squir- rels of all age classes and of both species. Such information was recorded systemati- cally under appropriate headings, as shown in fig. 3. For males, the information particularly sought was size and weight of testes and size of Cowper's glands ; for females, evidence of oestrus, pregnancy, lactation and placental scars. The age of all specimens was determined with as much accuracy as possible, and, throughout the study, special efforts were made to develop aging criteria. Weights and general measurements were taken of nearly all specimens. Other records related to locality and date of collection, condition of pelage, parasites, disease and stomach contents. Supplementing these data were detailed observations on foods and feeding habits, activity, behavior, habitat require- ments and other matters of ecological in- terest. Unfortunately, no fully satisfactory technique has been developed for censusing squirrels. That such a tool is important is obvious because the first information needed in management relates to the number of animals present on each study unit. This information is most useful when it supplies numbers at a definite time; for example, population in the fall. In the absence of standardized methods for determining squirrel numbers, it be- comes necessary to make the best estimates possible. These estimates are generally made by rules-of-thumb, or by using one or more of the various techniques that have been described. The result is often expressed in reference to the population by such terms as "plentiful," "common," "scarce," or "heavy," "medium," "light." Dice (1931) proposed, as the best method of determining mammal abun- dance, the listing of individuals observed in each ecological unit of the habitat. This September, 1945 Brown & Yeager: Squirrels in Illinois 453 method gives more properly an index of relative abundance in the various units rather than a true census. Later, Dice (1941) summarized various census tech- niques, some of which were applicable directly or indirectly to squirrels. Leo- pold (1933) discussed census methods for both game birds and mammals. Like Dice, he suggested techniques that could be used in squirrel census. Goodrum (1940) developed three cen- sus techniques for gray squirrels in Texas, which probably would be equally appli- cable to fox squirrels. These methods were as follows: 1. Time-area counts, using number of squirrels observed during definite time period on random plots of known size in each ecological type. 2. Nest counts in each ecological type, multiplied by a factor of two. 3. Hunting with dog, using number of squirrels treed per hour. The first method is based on the average distance a squirrel can be seen, and thus the size of the territory that may be ob- served from a stationary position. Good- rum, using three-fourths of this territory as the unit that could be watched effec- tively, calculated populations in each ec- ological type by multiplying the average number of squirrels seen per acre on each observation territory by the number of acres in the type represented. The second method involved counting all twig and leaf nests, preferably in the fall and win- ter, in each ecological type and multiplying by two. The third method, employed only when squirrels were active on the ground, gave the number of animals treed per hour in each ecological type. In each of these methods, the greater the number of counts and the more uniform the vege- tational types, the more nearly accurate is the census. It should be noted that Goodrum's first two methods result, theoretically at least, in a true census ; the third, unless several factors not given are known, could not be more than an index of relative abundance. The present writers made limited use of the time-area method and were convinced of its possibilities provided the investigator had time for making a large number of counts. In agreement with Allen (1942, 1943), who worked with fox squirrels in Michigan, we are uncertain of the value of of the nest-count method. The hunting- with-dog method was not tried. It is probably significant that Goodrum refers to these census techniques as " . . . methods found most effective in estimating gray squirrel populations in eastern Texas." Chapman (1937, 1938«) in Ohio, and others, have used data taken directly from hunters as a means of determining trends in populations. This is a rapid and use- ful method, and, if based on many samples, may indicate trends for large areas, even for a state as a whole. However, most kill data are subject to too many variations to yield more than very general informa- tion, thus limiting materiallv their use. Baumgartner (1940), Allen (1942, 1943) and the present writers determined, by exhaustive live trapping, and with a relatively high degree of accuracy, squirrel numbers on small study areas. This tech- nique, however, is too time consuming for practical, large scale censuses. Estimates of the population made by less exacting means, if based on experience and judg- ment, serve many purposes of manage- ment; and, if made uniformly year after year, may indicate population trends satis- factorily. Some experienced hunters de- velop almost uncanny accuracy in judging squirrel numbers on areas with which they are familiar. ACKNOWLEDGMENTS For aid in various aspects of this in- vestigation the writers are indebted to the following organizations and individuals. Illinois Natural History Survey: Dr. T. H. Frison, Chief, for general supervision ; Dr. George W. Bennett, Limnologist, for several photographs and for aid in collecting; Dr. Carl O. Mohr, Associate Entomologist, for suggestions in regard to field work; Dr. H. H. Ross, Systematic Entomologist, for identification of external parasites; Dr. D. H. Thomp- son, Zoologist, for assistance with statisti- cal analysis; Mr. Frank C. Bellrose, Jr., and Dr. Ralph E. Yeatter, for numerous records and suggestions; and Mr. James S. Ayars, Technical Editor, for several photographs and for assistance in the choice of illustrative material. Illinois Department of Conserva- tion : Hon. Livingston E. Osborne, Di- rector, and Mr. Anton J. Tomasek, State 454 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 Forester, for fiscal administration and many courtesies; Mr. Louis E. Martin, Superintendent of Game Restoration, for assistance with special problems; Mr. Robert C. Sparks, Chief Inspector, and numerous conservation officers for aid in collecting study material and in distrib- uting questionnaires. University of Illinois: Dr. L. J. Thomas, Associate Professor of Zoology, identified all internal parasites; Dr. B. V. Hall, Assistant Professor of Zoology, gave information concerning the physical characteristics of breeding in rodents ; and Dr. Robert Graham, Head, Department of Animal Pathology, cooperated in the study of a number of diseased squirrels. Gun Clubs AND Landowners: The following gun clubs extended to the senior writer many courtesies and provided a large number of squirrels for examination : East St. Louis Gun Club, Wolf Lake; Gilead Gun Club, Hardin; and Red's Landing Gun Club, Hardin. The fol- lowing landowners are among those who gave access to their property and assisted with certain phases of the study; Mr. Samuel Wade, Mr. Wayne Harshman and Mr. Frank Birch, all of Griggsville ; Mr. Robert Allerton, through Mr. Elmer Priebe, Monticello; Mr. Charles Price, Charleston. To many others, not named, the authors express their appreciation. POPULATIONS During the second year of the investi- gation, considerable time was given to study of squirrel populations on represen- tative areas in Pike County, in the central zone. From data gathered there, from questionnaires returned by hunters and from kill records supplied by the Illinois Department of Conservation, detailed in- formation on squirrel distribution, kill, sex ratios, species ratios and related subjects was obtained and added to the more general information gathered in the first year. Distribution The western fox squirrel, Sciurus Jiiger rufiventer (Geoffroy), the northern gray squirrel, S. carolinensis leucotis (Gapper), and the southern gray squirrel, S. c. car- oliiiensis Gmelin, are listed by Necker & Hatfield (1941) as occurring in Illinois. The fox squirrel has statewide distribu- tion ; records for the northern gray squir- rel include counties in approximately the northern two-thirds of the state and for the southern gray squirrel several of the southernmost counties, fig. 4. Both sub- species of gray squirrels undoubtedly ex- tend beyond the range given. The red squirrel, Tamiasciurus hudson- icus loquax Bangs, is listed by Necker & Hatfield as still being present in the wild in Illinois, but no observations or other records of it were obtained during the present study. If red squirrels occur here, it is believed that they do so only in re- duced numbers and in quite restricted lo- calities. Kennicott (1857) gives a good account of their early abundance in the northern parts of the state. Fox squirrels are found on farm and forested areas, and in cities and villages. Outside of some urban communities, gray squirrels are restricted to heavily wooded areas, generally those having abundant ground cover and brushy understory. ^ FOX SQUIRREL CRAY SQUIRREL Fig, 4.— Distribution of fox squirrels an^ gray squirrels in Illinois. September, 1945 Brown & Yeager: Squirrels in Illinois 455 Woodland of this type is found in Illinois principally along the main river valleys and in the southern and southwestern parts of the state, Hg. 4. Further discussion of the preferences of the two species are given under "Illinois Habitats." Density During this study squirrel population density vv^as determined with a high degree of accuracy on only one area. This area, however, was typical of the large region of good squirrel habitat in southern and southw^estern Illinois, where both squirrel species often occur in mixed populations. On three other areas, all representative of extensive Illinois habitat types, rough es- timates of the population were obtained. Population estimates of the four areas are presented in table 1 and are discussed below. Great differences in population density were found in Illinois fox squirrel habitats. Comparable data are not available for the gray squirrel. This species, however, is known to occur in varying densities, al- though not in the extremes found in the fox squirrel. The lack of extremes is due probably to relative uniformity in the habitat occupied by gray squirrels, which, as stated previously, is mainly heavily wooded areas. The populations given per acre for the Harshman and Urbana Town- ship areas, table 1, probably represent the highest and lowest densities for fox squir- rel habitats likely to be encountered in the state. On the Mason County area, which is of the black oak type, composed of all ages and degrees of stocking, it was found that fox squirrels may occur in varying densities in the same general habi- tat. The censused populations in 16 black oak stands in this area ranged from 0.02 to 2.20 squirrels per acre. Although many areas were found where both species were present, as well as many areas carrying only fox squirrels, none were encountered that held gray squirrels alone over a relatively large tract. Local concentrations of gray squirrels were often seen. The junior author counted 16 of these animals late in the afternoon of October 16, 1942, on an area of less than 3 acres. All were foraging in an oak- hickory stand that bordered a young river- bottom forest in Coles County. It Avas known that fox squirrels frequented this site. 1 he figure of 1.49 individuals per acre for the Wade area, table 1, probably represents for gray squirrels the upper density limit found on the better Illinois range. The figure of 2.23 fox squirrels per acre for the Harshman area represents the density on a small, very favorable area. A density of half this figure is considered as probably representative for large areas, even of the better habitats. No evidence was obtained to show con- clusively that either fox or gray squirrels are cyclic in Illinois. Fluctuations in populations from year to year, as long ob- served by hunters and reflected in kill records, suggest that these squirrels may be cyclic, although the degrees of fluctu- ation are only minor. If squirrel cycles operate at all in Illinois, they show little of the spectacular nature common in hares and other species in northern regions. Edminster (1937), at least by implication, suggested that the gray squirrel is cyclic in the New England region. Species Ratios From data presented in tables 2 and 3, and from general observations throughout the state, it is evident that the fox squirrel is more abundant than the gray squirrel in Illinois. All of the squirrels listed in table 3 and 86 per cent of the 4,597 animals in- cluded in table 2 were obtained by hunt- ing. Because of tw^o differentials associ- ated with hunting, the relative abundance of fox squirrels may be actually somewhat lower than the figures indicate. First, fox squirrels may be easier to kill than gray squirrels; they are so considered by many hunters, although the writers found little difference between the species in this respect. Second, there is a small differ- ence in the accessibility of habitat pre- ferred by the two species, that for the gray squirrel being, in general, the more re- mote and the more difficult and time con- suming for hunters to reach. On areas harboring presumably typical populations of fox and gray squirrels, both steel trapping and live trapping showed a preponderance of fox squirrels in the catch, table 2 ; in live trapping the differ- ence was small. In view of the first 456 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 I— I •a c C9 X! o c > c a u a o c O u '5 CD September, 1945 Brown & Yeager: Squirrels in Illinois 457 Table 2.—Species ratio in Illinois squirrels as determined from 4,597 animals, some of them shot by hunters and others collected by the writers, 1940, 1941 and 1942. 1 low Taki.n 458 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 Sex Ratios The sex of 4,651 squirrels, 3,197 fox squirrels and 1,454 gray squirrels, as de- termined during the investigation is shown in table 4. These data were de- rived largel_v from hunters' questionnaires, and were therefore subject to whatever differentials there may have been in bag- ging the sexes. It appears that Illinois squirrel popula- tions either have a preponderance of males, or that males are more easily bagged by hunters, who invariably shoot at squirrels in the order of their appearance until the limit is reached or the hunt is over. Fox squirrel males and females were taken in steel traps in approximately the ratios in which they were shot ; gray squirrel males and females were steel trapped in more nearly equal numbers, but with males pre- dominating, table 4. Live trapping, for which the samples are too small for re- liability, yielded in both fox and gray squirrels more females than males, but in gray squirrels the numbers were nearly equal for the sexes. Litter counts, on the basis of a very few samples, showed slight- ly more males than females in both species. A summary of figures listed in table 4 showed a preponderance of males in both species, giving a male to female ratio of roughly 60 to 40. The sex ratio of 17 litters of fox squir- rels, totaling 43 young, recorded during the spring of 1941 was 105 males to 100 females, table 4. Of 179 first-season or spring juvenile fox squirrels taken by the writers and by hunters from May through November 15, 62 per cent were males and 38 per cent were females; of 109 second- season or summer juveniles taken during September and October, 57 per cent were males and 43 per cent were females. The sex ratio of all juvenile fox squirrels for which records were obtained, including lit- ters, 195 males and 136 females, was 144 to 100. In gray squirrels, the sex ratio of 3 litters, totaling 11 young, was 120 males Table 4.—Sex ratio in Illinois squirrels as determined from sample litter counts and from animals shot, steel-trapped and live-trapped, 1940-1943. How Taken September, 1945 Brown & Yeager: Squirrels in Illinois 459 to 100 females, table 4. Of 60 spring October, 58 per cent were males and 42 juveniles taken hy the writers and b}' per cent were females. The sex ratio hunters, 55 per cent were males and 45 of all juvenile gray squirrels for which per cent were females; of 38 summer records were obtained, 61 males and 48 juveniles collected in late September and females, was 127 males to 100 females. 1 Fig. 5. — Juvenile (left) and adult male fox squirrels. Note smoothed, blackened appearance of scrotum in adult and the smaller, less conspicuous scrotum in juvenile. Piatt County, late January, 1944. Gray squirrels of the same ages show the same characteristics. 460 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 The actual sex ratio of Illinois squirrels may be more nearly equal in both species than shown in table 4. It seems that males, because of somewhat more active habits, offered hunters more opportunities to writers) placed some value on compar- ative growth stages, skin texture, and de- velopment of pigment and hair on various parts of the body, particularly on the scro- tal sac of the males and on the ventral Fig. 6.—Juvenile (left) and adult female fox squirrels, Mason County, August 15, 1944. Juvenile was first-season j-oung; adult had weaned a first-season litter, but was neither pregnant nor lactating. Note the inconspicuousness of the mammary glands of the juvenile, and the prominent, blackened nipples of the adult. for shots than did females, and probably for the same reason proportionately more males were taken in steel traps. Age Classes No simple, yet infallible, method of de- termining age classes in fox and gray squirrels has been reported. Such tech- niques are much needed, not only for squir- rels but for many other animal groups. The nearest approach to a workable method for aging squirrels requires the use of a number of criteria introduced by several workers, and validity of the method is somewhat conditioned by the experience of the user. For fox squirrels, Allen (1942, 1943) and Baumgartner (in letter region of females. Chapman (1938(7, b) working with gray squirrels, found a cor- relation of age and weight classes. In both species males were the more difficult of the sexes to age. Juvenile males born in late winter or early spring were easily confused wnth adult males by the October and November following ; and by December, when weights and measure- ments of the two groups were approxi- mately equal, they could scarcely be differ- entiated. In adult males the scrotal sac is more pendent, and is blackened and less nearly clothed by hair on the ventral sur- face, fig. 5. In December, appearance of the teeth, and of hair and skin on the soles of the feet, is very similar in the two age groups. Some juvenile males born in the I September, 1945 Brown & Yeager: Squirrels in Illinois 461 summer remain distinguishable from adult males until about May of the following jear. In females, the teats offer the best means of determining age classes. In individuals that have never bred, these structures are small, light in color, and with the entire gland more or less hidden in the growth of hair. Mature females, after breeding and nursing, have much larger and more conspicuous mammary glands, the nipples of which, in both species, are dark in color, fig- 6- . . The criteria found useful in aging squirrels in this study are listed in table 5. Collectively, and when used by an experienced observer, they are believed to be reliable for most individuals of both species. No single criterion w'as found applicable to all individuals of a given species or sex, and in some individuals age could not be determined with complete satisfaction when all criteria were used. Hunters distinguish young from adult squirrels by several criteria other than ap- pearance. The skinning test is perhaps most common, young squirrels being "easy" to skin and old squirrels "tough." Young squirrels remain "easy" to skin well into the fall or into the following spring, ac- cording to time of birth. The ease with which the leg bones may be snapped when the animals are being dressed is another criterion sometimes used by hunters. Squirrels may properly be classed as adults after they reach breeding condition, and on this basis first-season young, born in late winter or early spring, become Table 5.—Criteria for distinguishing between adult and Juvenile fox and gray squirrels. Adults Juveniles Males 1. 462 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 Pioj^ ON -a c o c o E Xi o c u aa o in 3 so 'Xi H u CJ w w ;?. J3qUI333Q jaqiuaAO^ jaqojDQ jaqiuaidag isngny Ajnf 3un{ Xejaj judv q^-n^IM Xjenjqaj ;{aBnuEJ" PWX J3qUI303Q J9qUI3AO;sI jaqojoQ jsqiuajdag AupM jsnSny Ainf 3un£ ludv T{DJEJ^ AJBnjqaj XJEnuBJ" -J U w o < w =^ OS y, o ao September, 1945 Brown & Yeager: Squirrels in Illinois 463 Table 7.—Age classes of squirrels shot or steel-trapped by the writers in Illinois during the hunting seasons of 1940 and 1941. 464 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 squirrels and gray squirrels. The occur- rence of one or both species on a given area appeared to be due more to characteristics of the habitat than to interspecific compe- tition or lack of it. Only two or three observations of belligerency, and none of actual fighting between the two species, were obtained, while, on the other hand, both were frequently observed feeding in the same area and sometimes in the same tree. Throughout the Illinois gray squir- rel range, hunters often kill both species on the same grounds. In one Pike County area, live trapping revealed a squirrel pop- ulation composed of 64 per cent gray squirrels and 36 per cent fox squirrels. Only fox squirrels inhabited an open, oak- hickory area a few miles away that was similarly trapped. Both species were col- lected with gun or steel trap on at least 50 areas throughout the state during the period 1940-1943. That some competition exists between the two species for available food and cover is probable, but it seems equally probable that little if any more compe- tition results from the presence of two species than from the presence of an equal number of individuals of the same species. The best evidence of interspecific compe- tition at hand is that usually only one species occurs in a given urban community. Seldom were both species found in any one municipality. We observed that about as many urban populations consisted of gray squirrels as of fox squirrels, although the habitat afforded by parks and tree-bor- dered streets is obviously better suited to the latter. DAILY ACTIVITY Throughout the first 2 years of this in- vestigation, squirrels were hunted at least weekly and often daily for the purpose of obtaining study specimens. The record kept of all hunts included the time of hunt (Central Standard), and the place and activity of each animal when seen. A to- tal of 716 hours, 387 in the morning and 329 in the afternoon, were devoted to hunting. Of the 554 squirrels observed, 336 were fox squirrels and 218 were gray squirrels. These data are summarized in table 8. Activity in both species of squirrels was decidedly greater in the morning than in the afternoon. In the forenoon, the hour between 6 and 7 o'clock, when an hourly average of 0.89 fox squirrel and 0.77 gray squirrel was seen, showed the highest ac- tivity figure for both species, table 8. The next highest activity hour in the forenoon was 7 to 8 o'clock for fox squirrels and 5 to 6 o'clock for gray squirrels. The greatest afternoon activity was between 4 and 5 o'clock for fox squirrels and between 5 and 6 o'clock for gray squirrels. Gray squirrels were active both earlier and later in the day than fox squirrels, but fox squir- rels were definitely more active during midday hours. The data in table 8 are not in accord with the observations of Hicks (1942), who found that the peak of activity in Iowa fox squirrels occurred between 8 : 00 and 10 : 00 A. M., and that the next highest peak was between 1 : 00 and 2 : 00 p. m. Hicks made only a limited number of ob- servations before 8 : 00 a. m. and after 5 : 00 p. M. Most other writers discussing this subject have indicated early morning and late afternoon activity peaks. The daily activity of both species was observed to reach the annual zenith during the mast season. At this time, storing ap- peared to be the main pursuit other than feeding, and in individual squirrels in- volved several hours per day. Gray squir- rels were observed to be abroad during midday hours more during the mast season than at any other time of the year except at the height of mating in December anc January. During the mast season, as at other times, there was more activity ir both species during early morning anc late afternoon hours than at midday. Although the effect of various weathei conditions on squirrel behavior was no studied in detail, both species were founc to be active all year, but least so during unusually cold weather. In hundreds oi observations made in winter examination; of wood duck boxes, it was noted that in^ dividuals of both species were somewhat sluggish and more or less reluctant to leave nest boxes when the temperature was be- low freezing. A total of 680 boxes yielded 55 squirrels, 48 of which were fox squirrels ; 32 of the fox squirrels showed noticeable reluctance to leave their nestS; Many of these individuals, which re- mained in the boxes after the lids were removed, were observed to be sleeping, September, 1945 Brown & Yeager: Squirrki.s in Illinois 465 Table 8.—Activity in Illinois squirrels based on 716 hours of hunting in which 336 fox squirrels and 218 gray squirrels were observed, June 1—October 31, 1941 and 1942. Hours specified are for Central Standard Time. Species 466 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 a well-defined direction; and "Dispersal," which deals with the phenomenon of spread or "shuffle" in squirrel populations, especially in the fall prior to the breeding season. Local Movements Both fox and gray squirrels are usually considered sedentary species, although the latter, according to some authors, are subject to irregular migrations, discussed below. As has been reported by Seton (1928), Baumgartner (1938, 1943^0, Goodrum (1940) and Allen (1942, 1943), local movements in both species of squirrels appear to be caused mainly by food conditions. In the course of a year, fox squirrels, apparently in foraging, may cross woodland or open fields for a dis- tance of 2 or 3 miles. Gray squirrels, where favored by continuity of forest cover, may travel equal if not greater dis- tances. The homing instinct of this spe- cies was studied by Hungerford & Wilder (1941), who reported returns in 6 of 15 animals, the greatest distance being 2.8 miles during a period of 4 weeks. Squirrels shift readily from one local food area to another. On the Chautau- qua National Wildlife Refuge, fox squir- rels deserted one area after another as specific foods in other areas became avail- able. They frequented the elm lowlands from late February into July, when elm buds and seeds, and later mulberries, sup- plied staple foods; they raided adjacent cornfields from midsummer until fall ; and they used upland oak-hickory areas as main foraging grounds during the fall and winter. These shifts, however, at no time involved travels of more than a few hundred yards, and in no sense did they take on the usual characteristics of mi- gration. In one wooded area on the Chautauqua Refuge containing mature oaks, pecans and hickories, in addition to elms, maples and other riverbottom species, seasonal shifts in the squirrel population (all fox squirrels) were much less distinct than those mentioned in the foregoing para- graph. Indeed, day-to-day travel here seemed to be confined to a small area, usually not more than a few acres, and often the vicinity of one or a small group of food trees. The annual range of the resident population covered only about 150 acres. During the young-rearing period par- ticularly, females seemed to confine their movements to the vicinity of their brood sites, which numbered from one to several. In both species local movements were most extensive during the fall. When not disturbed by overhunting, fire, drought or lumbering, individual squirrels may spend an entire year or more in the vicinity of a given nest tree. Allen ( 1942) reported an example of a Michigan fox squirrel female that used a red maple as headquarters continuously from Oc- tober, 1937, at least until observations were terminated in December, 1939. Seton (1928) stated that a gray squirrel may live its entire life on a 100-acre plot. Goodrum (1940) considered the home range of this species to be 200 yards or less, but he believed that some individuals may cover 4 or 5 miles during the course of a year. Middleton (1930) intimated that gray squirrels in Great Britain seldom travel more than 100 yards from head- quarters, but also stated that the species extended its range 35 miles in 5 years. Migration No evidence of migration in fox squirrels was observed in this study. Baumgartner (1938) writes: "General and regular mi- gration of the fox squirrel is unknown." Allen (1943) states: "Fox squirrels have seldom been observed in mass movements similar to those of the gray, which was known in early daj's as the 'migratory squirrel.' " There are numerous reports of mass movements or migrations of gray squirrels covering considerable distances; in these movements the animals were not deterred even by the formidable Avidths of the Hudson, Ohio or Mississippi rivers. Seton (1928) associated this phenomenon with food shortage, overpopulation and cyclic influences. Chapman (1936) at- tributed it mainly to the first two reasons. Jackson (1910, 1921) cited two instances in which numbers of the gray squirrel, in one case possibly because of a food short- age, swam the Mississippi River from Wis- consin to enter Minnesota. Goodwin (1934) reported an extensive migration in the New England states in 1931 and 1933. Osgood (1938) reported a. i September, 1945 Brown & Yeager: Squirrels in Illinois 467 gray squirrel migration of small propor- tions in Vermont in 1935. According to the reports of numerous authors, the mi- grations covering the most territory, as well as involving the most individuals, oc- curred before the twentieth century. Dispersal According to Baumgartner (1940), the most extensive and important movement in fox squirrels "is the traveling associated with the annual readjustment of popula- tions. This dispersal movement occurs between August 10 and September 15. J'he distances traveled at this time average about two or three miles, although two long records of 14 and 8 miles respectivel\ were secured. This movement is respon- sible for the annual restocking of over- hunted areas." Allen (1943) indicates that a popula- tion shuffle occurs in Michigan fox squir- rels. He states (1943) that "... it appears that increased activity among squirrels begins in late August, rises to a peak in late September, and is over by the middle of December." Of the reasons for dispersal Baumgart- ner (1943rt) writes: "The cause of this movement is controversial. The motivat- ing factor is usually considered to be population pressure correlated with a shortage of food, yet it occurs when the food supply is greatest, almost simul- taneously with the maturing of the nut crop. The moving squirrels are more noticeable when the population is high, and the writer believes the movement re- sults from intra-species intolerance. This view is partially substantiated by the fact that no record of excessive fox squirrel populations, either in the literature or in the field, could be authenticated. Seven such reports were investigated but none showed more than two squirrels per acre." Our evidence indicates that in Illinois a dispersal occurs in both fox and gray squir- rels during the fall. Continuous and in- tensive live trapping on the Wade area over a 10-month period prior to August 8, 1942, resulted in the capture and mark- ing of most if not all resident squirrels, since only one unmarked animal, a 1941 summer juvenile (female), was taken either by trapping or hunting during the period between July 12 and October 15, 1942. Ihis individual was trapped on August 5, and it is likely that the squirrel had only recently moved onto the area from a woodland to the east. On August 8, 1942, the writers shot two fox squirrels (Nos. 11 and 26) and seven gray squirrels (Nos. 1, 5, 9, 13, 26, Zi and 50) on the Wade area. No unmarked animals were among these squirrels. In the period Oc- tober 15 through 17 the senior writer shot 13 additional specimens, 5 fox squirrels and 8 gray squirrels, of which 1 fox and 2 gray individuals were unmarked. They were 1942 spring juveniles, and therefore subject to trapping and marking had they been present during the last 8 to 10 weeks of trapping. It is believed that these three animals had moved onto the area during the period of August 8 through October 17. Other than these three spring juveniles, six unmarked 1942 summer juveniles (one fox, live gray) were collected in mid October, 1942, but these may have been young born on the area and too small to be taken in live traps prior to August 8. CONDITION Weight and length measurements w^ere taken of most squirrels collected, and in- formation on diseases, parasites, deformi- ties and pelage development was recorded when observed in the specimens. Weight Weights were obtained for a total of 706 fox squirrels and 317 gray squirrels. The data are given in table 9. In adults, weights were recorded by sex, but in juveniles the weights of the two sexes were lumped. As indicated in table 9, there were no significant differences in weight between male and female adults in either species. Allen (1942, 1943) found female fox squirrels in Michigan to be slightly larger than males. A point of interest in the present stud>' is that of size in juveniles at the time the\ began to enter hunters' bags in July. Spring juvenile fox and gray squirrels at that time had an average weight of 1.28 pounds and 0.84 pound, respectively. By late October or Novem- ber, the spring juveniles of both species had reached approximately average adult 468 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 e OS ot ON M in < O -a 0) 9> o S o* o c w 3 X o 3 O a •of '53 o\ IE
  • 3 .S -5 J— Qj 3 K H o J3qiun|y[ 3SBJ3AY J3quin|sj 3§EJ3AY jsquin^ 3SbJ3AY J3quin]sj^ 3SBJ3Ay J3quin|y[ 3gBJ3AY jsquin^ Jl{gl3A\ 33BJ3Ay J3qutnjvj ;qgi3^ 3iB43AY J^qlun|^J^ -H CS * ^ OS Cs O On * t^ oo oo NO r^ r^ ON o o -^ o o o o o NO r-- ij-1 Tt< Tf ur, Tt< ON (N r--* NO OO ON O C^l o o o o ^ — ON ON <-o r^ oo t^ cooo-^tor^noNNDootfr^ CN (N On oo NO O T— I c-i ON CO r^^ Tt^ '^ ^ O -H ^ ^ ^ On r^ w-1 w-1 iy-1 r^ Tt< Tfi T^ Tf NO oo r^ cN NO >-H OO ^H 04 CO >^ NO NO r-^ ^^ CO CO c-J CO *— I CN CN OO CO ^-i Tt<.-^ONcx)cO'-^'-^r^or^ON-^ r^r--'j-i^ONOt^t^NDr~r--Nor-^ OON--HtNNO'*NO^ONr^>-OND r~~cs-r-ir~~"iONcoNO-*'^H-^r^ r~-Nor--NDNONor^NONor-^oor^ re 3 u .^ 3M 3 < on (-1 u 6 j-iONcoco-*r--NO-- squirrels killed near Rock- ford, Illinois, all were black. During the pioneer period, black squirrels were com- mon in Michigan (Allen 1943), Indiana (Haymond 1869, Hahn 1909) and in other states. One adult male gray squir- rel trapped in Pike County, February 25, 1941, had reddish thoracic hair and black abdominal hair. A juvenile male fox squirrel with blue eyes was trapped in Pike County, February 8, 1942. Baum- gartner (1943/*) reported nine different color patterns in Ohio fox squirrels, in- cluding melanistic, near albino, brown- tail, and variations of black and red or rufus. PARASITES AND DISEASES Several papers dealing with the para- sites of squirrels, particularly fox squirrels, have been published. Katz (1939) brought most of this information together. Harkema (1936) studied the parasites of 53 gray squirrels in North Carolina, find- ing one species of tapeworm, one of round worm, three of mites, two of lice and one of flea. Chandler (1942) recently re- ported on the helminth worms of tree squirrels in southeast Texas ; and Graham & Uhrich (1943) published on the ex- ternal and internal parasites of the fox squirrel in southeastern Kansas. Baum- gartner (1940) and Allen (1942, 1943) discussed briefly the parasites and diseases of fox squirrels in Ohio and Michigan, respectively-; and Goodrum (1940) re- ported similarly for gray squirrels in Texas. The most prevalent parasites re- ported by all these authors were mange mites. No diseases of endemic nature other than mange were reported. Most squirrels studied during 2 years of field work in this investigation were examined for mange, and for ticks and other external parasites. The same spe- cies of parasites were found to occur on both fox and gray squirrels. Mange (caused by Sarcoptcs sp.) occurred to a 472 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 noticeable degree in only 0.03 per cent of the 722 fox squirrels and 0.06 per cent of the 353 gray squirrels examined for this condition. Incidence of mange in all squirrels studied was 0.04 per cent. All zones were represented by the animals examined for parasites. The degree of infestation was negligible in most woodland populations, but in some urban populations of both species a heavier rate prevailed. Woodland squirrels show- ing evidence of mange were found on only two localized areas, one the pin oak bot- toms near Thomson in Carroll County, involving only fox squirrels, and the other near Griggsville in Pike County, involving both fox and gray squirrels. The first area showed an infestation of 47 per cent in a sample of 15 squirrels; the latter, 15 per cent in a sample of 94. The degree of infestation in Pike County was about the same in the two species. In both localities squirrels were collected during the breeding seasons, and in both infested individuals were apparently normally ac- tive. A female shot February 26, 1941, on the Thomson area had bare patches of skin on head, neck and back, yet contained three well-developed embryos. Another collected on February 17, 1945, near Mon- ticello, Piatt County, had the left hind foot missing and was practically devoid of hair, due to mange, on the neck and thoracic regions, but this animal, fig. 7, likewise contained three normal embryos. None of the infested squirrels were in poor physical condition. Practically every squirrel, fox and gray, was host to fleas ; many animals carried the common dog tick ; less than 1 per cent carried sucking lice. Dr. H. H. Ross of the Illinois Natural History Survey sup- plied the following notes on ectoparasites. The same species of ectoparasites occur on both the gray and fox squirrels in Illinois. Ticks (Ixodoidea) Dermacentor 'variabilis (Say).—Taken very commonly on squirrels throughout Illinois. This is the common dog tick and occurs on many other mammals. Parasitic Mites (Parasitoidea) Several species of this superfamily of mites have been encountered on Illinois squirrels. Fleas (Siphonaptera) Orchopeas ho^vardii (Baker).—Very common and frequently extremely abundant. This species has been found in great numbers in overwintering nests throughout Illinois. Orchopeas nepos Rothschild.—Taken only rarely in Illinois. Sucking Lice (Anoplura) Hoplopleura sciuricola Ferris.—Taken only rarely in Illinois. In addition to the above, chiggers undoubt- edly occur on Illinois squirrels. Although we have no definite records for this state, Roger Williams, while at the University of North Carolina, found chiggers on squirrels. These chiggers belong to the mite genus Trombicula and allied genera. In a small number of squirrels studied for internal parasites, one-third of the animals contained parasitic worms. Iden- tification of these specimens was made by | Dr. Lyell J. Thomas of the University of Illinois. The following remarks are quoted from his report. No. 1.—Female fox squirrel, Thomson, Illi- nois, collected May 27, 1941: Eight cestode cysts in visceral cavity, identified as Taenia pisiformis. These generally occur in rabbits. No. 2.—Female fox squirrel, Griggsville, Illinois, collected April 19, 1942: Several nem- atodes from intestine ; all females, and identi- fied as Impalaia sp., probably new. No. 3.—Female fox squirrel, Griggsville, Illinois, collected August 7, 1942: One large male nematode from large intestine identified as Ascaris sp. (probably A. lumbricoides). Has been recorded from East Indian squirrels, but not, to my knowledge, from North Ameri- can squirrels. Normal hosts are man and pig. Closely allied species occur in skunks and armadillos. No. 4.—Female gray squirrel, Griggsville, Illinois, collected April 21, 1942: Three male and five female nematodes from intestinal tract identified as Impalaia sp., probably new. Two female nematodes from intestinal tract identi- fied as Mescistocirrcus sp., probably new. The four squirrels yielding the above endoparasites appeared to be in normal vigor, although none contained noticeable fat in the body cavity. The female that was host to the ascarid was reddish to the point of erythrism. The uterus showed five placental scars and the mammae con- September, 1945 Brown & Yeager: Squirrels in Illinois 473 tained milk. This squirrel weighed 1.59 pounds, was 544 millimeters in total length, and had about half completed the molt. A female fox squirrel, too weak to escape, was captured alive near Urbana, Illinois, on April II, I94I. Diagnosis in the Animal Pathology Laboratory of the University of Illinois revealed a fractured tibia and the presence of hepatic coccidio- sis. On August 5, 1943, Dr. R. E. Yeatter of the Illinois Natural History Survey collected near Urbana a very weak female fox squirrel ; diagnosis in the University's Animal Pathology Labor- atory "... revealed the presence of small, circumscribed white foci in the liver and spleen. In view of these lesions and the history of the squirrel having been found sick, we regard the possibility of tularemia in this animal as being quite good . . . cultures were not made." This female had recently nursed young. The writers and others of the Illinois Natural History Survey staff sometimes found dead squirrels in wood duck nest boxes. Usually these squirrels w^ere so badly decomposed that cause of death could not be determined. The number of squirrels found dead was not great, and the over-all evidence suggests that no ap- preciable number of these animals die of diseases or the effects of parasitism. PREDATION Predation losses in squirrel populations are unimportant in Illinois. There are numerous published reports of squirrels being taken by hawks, owls, dogs and other predators, but the writers found little evidence that such losses reach serious pro- portions in this state. Extreme agility and a speed that attains a maximum of 12 miles per hour in the fox squirrel (Cottam 1941), and probably an equal speed in the gray squirrel, enable both species to elude most predators effectively. In January, 1941, in the examination of 680 wood duck boxes, one weak male fox squirrel was found that showed con- clusive evidence of having been attacked by a raptoral bird. Talon punctures on the dorsal surface reached to the body cavity. Mange was present under the forelegs and about the hocks. When re- leased, the squirrel appeared dazed and climbed back to the box with difficulty. Two months later another inspection re- vealed that he had died in the box. No sign of gunshot or other injury could be found. A northern Illinois coon hunter reported one instance of weasel predation on fox squirrels. This attack was at night. The hunter first heard a squirrel in a tree, then a crash, followed by a struggle on the ground. With the aid of a flashlight the hunter saw the squirrel and weasel plainly. The squirrel escaped, but it is not knov\n how badly it may have been injured. The senior writer once flushed a feral cat that w'as obviously trying to stalk a barking fox squirrel. On snow' in north- ern Illinois he observed a red fox stalk a fox squirrel that was busily engaged in eating an Osage orange fruit, but the fox was frightened before reaching a springing position. On another occasion the senior author saw a red fox leap upon and cap- ture a badly wounded fox squirrel, but shouts caused the fox to drop its victim and dash away. Fox and gray squirrels caught in steel traps were occasionally attacked by hawks, free-ranging dogs and other predators. The red-shouldered hawk and red-tailed hawk were the only raptors actually flushed from trapped animals. A trapped fox squirrel, caught late in the afternoon, was killed during the night by a weasel. Dogs are known to have eaten three fox squirrels and one gray squirrel caught in traps. It is recognized, of course, that trapped squirrels attract the attention of predators and offer easy prey, making them unreliable criteria for measuring predation losses. BREEDING The term breeding as usually employed in this study includes pre-mating behavior, mating and such physiological aspects of breeding as oestrus, pregnancy, testes de- velopment and changes in the Cowper's glands. During the period of investigation, data on breeding or young rearing were ob- tained from a total of 4,790 squirrels, which are listed in table 1 1 by species and according to time and manner collected. The 1,075 squirrels shot or steel-trapped by the waiters and used for detailed 474 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 Table 11.—Squirrels counted or collected for study in Illinois, 1940—1943. How Collected OR Counted September, 1945 Brown & Yeager: Squirrels in Illinois 475 a second time, that is, during the summer, in their first 18 months after birth. Fe- males from summer litters are usually too immature to breed during the ensuing winter season, at an age of 7 months or less, but they breed during the following summer, at an age of about a year, 'i'he gray squirrel has been found to 1 he annual breeding cycle of males in Illinois was found to coincide approximately with that of females, but the two peaks are less distinct in the males, which appear to be in breeding condition continuously from late fall to midsummer, although a minor decline is apparent in February and March, fig. 9 and table 14. The data Table 13.—Generalized peak mating dates of squirrels in three Illinois zones, based mainly on 2 years of study. .July 1, 1940, to June ?>(). 1942. 476 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 per's glands and evidence of oestrus. In the first three characteristics, all peculiar to males, there was close similarity but not exact uniformity in the two species. In both fox and gray squirrels, testes length and weight peaks were reached before or by the time of peak mating. It is evident that none of the criteria based on male organs are fully satisfactory for determining the breeding seasons, and for this reason we have placed greater reliance in the percentage of females showing oes- trus, fig. 8, assuming that peak oestrus and mating occur simultaneously, or nearly so. Dates given in table 13 are in general agreement with findings reported by other workers. The chronology of squirrel breeding data in Illinois, including the earliest, latest and peak dates for various repro- ductive activities or conditions, are given in table 16. Peak dates are applicable OESTRUS dJ 80 10 3 60 tO LJ O40 z to H 20 u I L. _l L. a September, 1945 Brown & Yeager: Squirrels in Illinois 477 8 7 6 E i 4 O UJ -a 478 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 * o c 3 O OS "a i-S -a c o C3 o c s u E 3D C3 "> U « OH •5 u u September, 1945 Brown & Yeager: Squirrels in Illinois 479 I 480 Illinois Natural History Survey Bulletin Vol 23. Art. 5 Table 16.—Chronology of breeding in female squirrels in Illinois; data obtained mainly July 1, 1940, to June 30, 1942. Peak dates are applicable particularly to central zone. September, 1945 Brown & Yeager: Squirrels in Illinois 481 The writers believe that most of the females not breeding during the first or winter season fail to do so because of im- maturity or senility. Of the two causes, immaturity is probably the more common. Probably poor physical condition is the most important cause of the failure of some old females to produce the second- season litter. The first and last dates of reproductive condition or activity observed in Illinois during this study and the apparent season duration are given in table 17. Season length appears to be about the same in the two species. into two or more separate chases. The chases involving nine and six gray squir- rels, respectively, occurred late in the fore- noon. Observations similar to the fore- going w^ere made by Baker (1944) in Texas. In both species, barking or "chatting" was noticed more in December than in any other month, but it was more or less common throughout the summer, fall and early winter. Intermittent barking may occur during any month. Although bark- ing is characteristic of mating behavior, it may, of course, denote alarm, surprise, anger and probabl\' other reactions. Mating Chase The most obvious indication of breeding seasons in squirrels is the mating chase. Fox squirrels appear to be shier than gray squirrels in their mating activities. During the present study, the number of mating chases observed, in proportion to populations, was less in fox squirrels ; like- wise, the average number of fox squirrels per chase was less. Seldom w^re more than three fox squirrels observed in a single chase, whereas, in gray squirrels, observations were made on chases of nine and of six animals, and many of five or less. The average mating group, how- ever, even in gray squirrels, involved only three or four animals. Chases were en- acted indiscriminately in trees, on logs and on the ground. In the chase in which nine gray squirrels participated, two of the animals were fe- males, and it is believed that the remaining seven were males, one a juvenile. The two females barked continuously. One female, despite her calling, turned and fought the nearest male when pursued too closely; the other, when chased into isolated positions, such as the smaller branches of a tree, was mounted by several males, but copulation was not observed. One of the females was mounted as she raced up a tree, but she fell upon reaching the top, whereupon the male lost his position. The nearest pursuing male often turned to drive back his rivals. This chase covered an acre of dense un- dergrowth, lasted about 20 minutes, and was well advertised by continuous barking and noisy quarreling. Chases involving a large number of squirrels sometimes split Physiological Aspects In studying the physiological aspects of breeding, it was necessary, due to limita- tions of personnel and to field conditions, to rely upon gross laboratory examination rather than the more precise technique of vaginal smears and gonad sectioning with microscopical study. Mossman, Lawlah k Bradley (1932), who studied the male squirrel reproductive tract, including the Cowper's glands, re- ported the male reproductive organs in fox and gray squirrels to be similar. Testes.—In both species the testes, fig. 10 and table 14, began to enlarge in Sep- tember. In mature males, enlargement was from a flaccid to a turgid condition. For the first breeding season the maximum average testis length, December 1-15, was 30.4 millimeters in fox squirrels, and, De- cember 16-January 15, 27.7 millimeters in gray squirrels. Testis length during the second breeding season was slightly greater than in the first or winter season in fox squirrels, but slightly less in gray squirrels. Following the second season, the testes became much smaller and ap- parently inactive; the minimum average length in mature males for any 15-day period was 20.4 millimeters in fox squir- rels and 19.0 millimeters in gray squirrels. These measurements were reached in late August and early September, respectively-. At this time, the testes may have been drawn into the abdominal cavity, and the dormant-like condition have continued un- til some time in September, when the organs began an increase in size that con- tinued until the winter maximum was reached. Testes measurements for juve- 482 Illinois Natural History Survey Bulletin Vol 23, Art. 5 nile males were, of course, much smaller after which development was rapid. The than for adults, the difference being great- maximum diameter of the glands in each er in the fall than in the spring. species was about 25 millimeters, reached Weight of testes, which may be a some- during the latter half of December. The what more accurate indication of breeding spring maximum observed was about 23 Fig. 10.—Testes of adult and juvenile squirrels. A, adult fox squirrel ; B, adult gray squirrel; C, juvenile fox squirrel; D, juvenile gray squirrel. Epididymis removed in right example of each pair. Coles and Piatt counties, late January, 1944. stage than testes length, showed greater fluctuation during the breeding seasons than the length measurement. In fox squirrels, peak average weights of 7.38 grams and 7.84 grams for the testes were reached in late December and late April, respectively. In gray squirrels, corres- ponding data, less reliable due to fewer samples, averaged 6.16 grams for the testes early in January and 5.73 in May; the average of a small number of samples in early April was 5.80 grams. Adult and juvenile testes are illustrated in fig. 10. Gowper's Glands.—The location, large size and relationship to breeding activity of the Cowper's glands make them a good criterion by which to judge the sexual condition of males. These glands, fig. 11, are paired, discoid bodies, the function of which is production of sperm- carrying fluid. The glands, coiled like a Polygyra snail shell, are situated one on each side of the rectum. Connection with the penis is by duct. When turgid, these glands extend posteriorly, distending the anal orifice and increasing the average body length by about 10 millimeters. Enlargement in the Cowper's glands in both species was first observed in October, millimeters, attained about the end of May in fox squirrels and the last 2 weeks of June in gray squirrels. The number of gray squirrels examined was so small that the data for them may not be representa- 1 tive; comparable data for the fox squirrel indicate that the peak diameter of Cowper's glands in the gray squirrel was reached earlier in June than is shown in table 14. Following cessation of breeding in the summer, these glands be- came dormant and decreased so greatly m\ size that, in August, September and Oc- tober, they were diflfiicult to find, even by dissection of the animals. Scrotum.—Field observations showed that, as the breeding season progressed, the scrotum became comparatively smooth, and both skin and hair assumed an oily, brown-stained appearance, fig. 5. Follow- ing the mating season, in June or later, the scrotum lost this rubbed, blackened appearance through sloughing of the skin and replacement of hair and underfur in the molting process. The new skin of the sac was of lighter pigmentation, as in juve- nile males, fig. 5. In "old squirrels, the loose saclike condition of the scrotum pre- vailed, whereas in juveniles, because ofi September, 1945 Brown & Yeager: Squirrels in Illinois 483 the more abdominal position of the testes, the scrotum was less pendent. Oestrus.—The earliest evidence of first-season or winter oestrus observed in fox squirrel females was December 11 in Alexander Count\^ (southern zone), tables 15, 16 and 17. The latest oestrus records for the first season in the southern and central zones were Januarj' 27 ; the two observations were a year apart. In gray squirrels the earliest evidence of winter oestrus was December 16, and the latest was February 11, both observations in the southern zone. The external indication of oestrus, commonly called "heat," is a swollen, pro- truding condition of the vulva. During oestrus the uterus is enlarged and con- gested with blood, by w'hich the vulva is commonly discolored. This condition is easily observed in external examination. Following copulation the congested con- dition of the uterus clears. The uterus becomes spongy and thick-walled, and fetal nodes, 3 millimeters in length, appear about 10 davs after successful coitus. Pregnancy.—An attempt was made early in the survey to distinguish oestrus and early pregnancy by the use of vaginal smears, but this proved impractical under conditions prevailing in the field. The oestrual period thus was probably not dis- tinguished as precisely as is desirable, and perhaps an unknown number of very early pregnancies were listed under the heading of oestrus. Pregnancy could be determined with some certainty by noting the relaxed and perforated state of the vulva and development of the mammae. Somewhat advanced stages of pregnancy (15 millimeter fetuses) could be detected by palpating the lower abdomen. The earliest and latest first-season pregnancy records for fox squirrels were January 1 (one animal with 3 fetuses averaging 6 millimeters in length) and March 22 (one animal with 3 fetuses averaging 19 millimeters in length), table 16. The first-season peak of fox squirrel pregnancy, based on 43 adult females, 23 of them pregnant, table 15, came during the first half of February. In gray squir- Fig. 11.—Glans penis and urethra of adult male squirrel, with Cowper's glands attached in an uncoiled and in a nearly natural position in each case. Left, fox squirrel; right, gray squirrel. Coles County, late January, 1944, 484 Illinois Natural History Survey Bulletin Vol. 23. Art. 5 rels, the earliest and latest pregnancy records were January 13 (one animal with 2 fetuses averaging 4 millimeters in length) and March 29 (one animal with 3 fetuses averaging 15 millimeters in length), table 16. Peak gray squirrel pregnancy for the first season, based on 16 adult females, 9 of them pregnant, came about the middle of February, table 15. The earliest and latest second-season pregnancy records were June 19 and August 29 for fox squirrels, and July 5 and September 9 for gray squirrels, table 16. Fox squirrel females taken on August 15 and 29 each contained 2 fetuses; those of the first averaged 20 millimeters in length and those of the second 48 milli- meters. Fig. 12 shows embryos at the age of about 15 days in the uterus of a fox squirrel. Gestation.—Previous writers have re- ported difficulty in determining exactly the Fig. 12.—Uterus of pregnant fox squirrel. Right horn contains two normal fetuses and one apparently in process of being resorbed, September, 1945 Brown & YEAGtR: Squirrels in Illinois 485 Fig. 13.—Lactating gray squirrels, Coles County, September 15, 19+4. Note Histended ap- pearance of mammary glands and nipples. gestation period in squirrels. Allen (1942, 1943) and Lyon (1936) indicated that gestation in fox squirrels is probabh' about 45 days. Since the oestrual peak in this species in Illinois, as determined by the present study, was late in December and early in January, a 45-day term would place the birth peak in February. The oestrus records in table 15 and the birth records in table 18 indicate that the ges- tation period in Illinois fox squirrels is about 45 days. Seton (1928, 4:44), quoting Powers, gives the gestation period in gray, squirrels as 44 days. Goodrum (1940) and Baumgartner' (1940) also considered that 44 days was the probable term. The oestrus-mating peak in the small number of gray squirrels observed in the Illinois study was early or mid January, table 15, and the birth peak was early March, table 18, indicating an av- erage gestation period of about that sug- gested by Goodrum, Baumgartner and other authors mentioned above. Mammae.— In both fox and gray squirrels, the mammae are eight in num- ber and are arranged in four pairs, oc- cupying the ventral body surface behind the forelegs, fig. 13. Allen (1942) des- ignated the mammae positions as pectoral 1, pectoral 2, abdominal and inguinal. He stated that, in the fox squirrel, the abdomi- nal pair develops first following insemina- tion, and that the usual order of develop- ment is abdominal, inguinal, pectoral 2 and pectoral 1. In some cases, however, Allen found that the pectoral 2 and ab- dominal pairs developed equally, or the former preceded the latter in development. The pectoral 1 pair may not be functional in some cases. Milk can be squeezed from the nipples a few days before the young are born and, in some cases at least, for 2 or 3 weeks after the young are 486 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 weaned. Thus the glands may contain milk for 3 months or more subsequent to parturition. The teats and mammary glands of squirrels develop rapidly after pregnancy begins. In both species, the teats swell and become black pigmented. The glan- dular tissue becomes thickened and spreads to cover the ventral body surface. Hair on the mammae of nursing females be- comes worn and matted, and the nipples show^ an obviously distended and stretched condition, fig. 13. On cessation of lac- tation the teats become greatly reduced and, in fox squirrels at least, the black pigmented condition of the nipples remains apparent, fig. 6. YOUNG REARING In the term young rearing, as it is usually employed in this paper, are in- cluded the biological phenomena associated with young squirrels. Birth Dates In the spring of 1941 birth dates were estimated for 35 litters of fox squirrels and 4 litters of gray squirrels. Most of Table 18.—Birth dates by 2-week periods for 35 fox squirrel litters and 4 gray squirrel litters in Illinois, all zones, spring, 1941. Species September, 1945 Brown & Yeager: Squirrels in Illinois 487 the litters had been born in wood duck nest boxes, but a few of the fox squirrels in leaf nests. The distribution of esti- mated birth dates by 2-week periods is shown in table 18. In addition to the fox squirrel births included in table 18 were those involving two nursing females taken on February 20 and another on February 21. In these animals the uterus had returned to ap- proximately normal size and all showed placental scars. Scars do not appear until the uterus has cleared, several days follow- ing birth of the young. The earliest first-season birth date es- timated for Illinois gray squirrels (only four litters observed) was February 20 and the latest March 18. One pregnant gray squirrel female, almost to term, was taken March 29, indicating first-season young are born at least through March. No birth records were obtained for the second season in 1941, or for either the first or second season in 1942. From the numerous records of oestrus, pregnancy and lactation in both species, however, the birth peaks can be approximated. Birth Sites Because squirrel dens and leaf nests are discussed later in this report, no details on birth sites are given here. Although \oung are born in both cavity and leaf nests, it appears that the cavity type is preferred. More litters were found in natural cavities than in leaf nests, and many litters were found in boxes construct- ed and erected for wood ducks. The senior author checked, on the Mason County State Forest, a total of 89 leaf nests during the first half of April and found only 2 litters of partl_\' grown fox squirrels. Only fox squirrels inhabited this area. Goodrum (1940) states that in east Texas gray squirrels are usually- born in hollows of trees, but that they may be transferred to leaf nests. Both species move their young from nest to nest when disturbed. On such occasions the mother grasps the young in her mouth, in the manner of a cat moving her kittens. Lactation The young of both fox and gray squir- rels nurse for 8 weeks or more. The earliest and latest records of lactation during the first season are for fox squir- rels, February 20 and May 27 ; for gray squirrels. March 1 and May 31, table 16. Most fox squirrel females had finished nursing by May 1 ; most gray squirrel females by May 15. Lactation data for both species and for both breeding seasons are given by 2-week periods in table 15. As indicated in table 15, lactation in the Illinois fox squirrels studied was most prevalent in March and August, when 78 and 44 per cent, respectively, of the adult females handled showed this condition. In gray squirrels, lactation was most prev- alent in April and September, when 75 and 60 per cent, respectively, of the adult females handled were nursing. In some females the cessation of lactation was found to be delayed. In both species, females showing second-season oestrus still carried first-season milk, which could readily be exuded by pinching the nipples. The young observed during the study were weaned when about 8 or 10 weeks old. Development of Young Fox squirrels handled shortly after birth were 50 to 60 millimeters in length and weighed 14 to 18 grams (about one-half ounce). They were dark pinkish, naked, except for vibrissae about the nose and chin, and virtually helpless. The claws were well developed. Both the eyes and ears were closed, and neither the upper nor lower incisors had erupted. The vibrissae grew rapidly, and hair first appeared on the upper dorsal surface at an age of 8 or 10 days. Further growth character- istics are detailed in table 19, data for which were obtained principally from caged animals. Because of a growth differential be- tween caged and wild specimens, the data in table 19 may vary from corresponding data for wild squirrels by 2 or 3 days. Information relating to pelage is prob- ably subject to wider variation than that pertaining to eyes, ears, teeth or weight. There was no opportunity during the study to weigh or measure gray squirrels at birth. These animals are smaller and somewhat lighter in color than fox squir- rels. At weaning age, or during late April and May and late August and September 488 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 I— I -a c ca c 3 O u u cs u c V u ^3 e U c >. .A 13 0) ca a o u '3 s 4) o n September, 1945 Brown & Yeager: Squirrels in Illinois 489 for most individuals, fox squirrels were found to average about one-half pound in weight; gray squirrels, on the basis of a very few samples, about one-third pound or somewhat less. By mid June, young fox squirrels handled averaged slightly more than 1 pound, and young gray squir- rels about 0.6 pound. At the time of weaning the pelage in both species, including that of the tail, was well developed. The young animals were active, being able to leave the nest and, with some awkwardness, to forage for buds and other food. Manual dexterity in gray squirrels seemed to develop some- what more rapidly than in fox squirrels. At or near weaning age the young of both species began to join the adults in travels, and were often observed in litter groups feeding on elm seeds and buds in the spring, and acorns and hickory nuts in the late summer and early fall. It is doubtful, however, if 8- to 10-week old squirrels are fully self-sustaining. Allen (1942, 1943) considers that fox squirrels are not self- sustaining until they are between 3 and 4 months old, a belief shared by the present writers. Development in first- and second- season squirrels appears to be at about the same rate. Litter Size The average size of litters in Illinois squirrels was determined by counts of young in nests, of fetuses and placental scars, table 20. As found from study of 85 litters of fox squirrels and 34 litters of gray squirrels, the average size of litters in grays was somewhat larger than that in fox squirrels, but the difference was not significant. Neither was there a great difference in the size of the first- and second-season litters in either species. Gray squirrels showed the larger average in the first season; fox squirrels the larger in the second season. During the course of this study, in- teresting data were gathered on the pos- sible effect of food quality on fecundity. The investigation was conducted mainlj on the rougher, wooded parts of Illinois, where soil fertility is comparatively low, and where the staple squirrel foods con- sist principally of nuts, acorns, fruits, berries and buds. Other investigators in Illinois, working on the more fertile ag- ricultural areas where corn is the main staple, found that litter size in fox squir- rels there was larger than was found by the writers on wooded range, table 21. The nutritional value of corn is prob- ably greater than that of the combination of nuts, acorns, buds and fruits of wooded localities, and since, on most Illinois farms, corn is abundant at all seasons, either at cribs or in fields, farmland fox squirrels in this state are well nourished. Most woods-inhabiting squirrels in Illinois ap- pear to suffer no serious food shortages, Table 21.—Litter size in fox squirrels in two types of Illinois habitat, 1941 and 1942. 490 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 but midwinter supplies are often less abundant in the woodlands than in farm regions. The difference in average litter size in the two habitats, as shown in table 21, is significant. The writers believe that the superior quality and quantity of food characteristic of many farmland hab- itats may be the main reason for the differ- ential in litter size. No comparative data are available for gray squirrels, but it is of interest that 34 litters found in wood- land types averaged 2.68 young, table 20, a number smaller than the average for farmland fox squirrels. ILLINOIS HABITATS Forest cover is the basic requirement of fox and gray squirrel habitats, and the kinds, combinations and sizes of the trees, shrubs and brambles they contain, and the include them under two main headings : black prairie and woodlands. Black Prairie Habitats The black prairie region of Illinois is overwhelmingly agricultural and is dom- inated by the production of corn, soybeans and wheat. It contains very little wooded area, and therefore has an acute shortage of den trees. Subtypes making up the squirrel range in this region are woodlots, wooded stream bottoms, hedgerows, and fields and farmyards with scattered trees or groves. The woodlots are predomi- nantly oak-hickory. Walnut plantations are widely scattered and aggregate only a very small acreage. In the bottoms, the main trees are elms, maples, sycamore, white ash and other wet-site species ; and on the bluffs, oaks and hickories are the Fig. 14.—Typical farm habitat of fox squirrels on Illinois black prairie type, Champaign County, February, 1941. density of the stand, to a large extent determine their quality. Since the oc- currence and growth of woody vegetation vary with soil, climate and the activities of man and other animals, the types of squirrel habitats in Illinois are many. Although the variations in squirrel habitats are not readily classified, it is possible to principal trees. The only important hedgerow species is the Osage orange, the older and larger hedges of which are now steadily being pulled. Practically all wooded areas on the black prairie are grazed. Staple squirrel foods' in this region, in probaljle order of importance, are corn. September, 1945 Brown & Yeager: Squirrels in Illinois 491 Fig. 15.—Mature elm-maple river-bottom type, Piatt County. Pin oak through the northern two-thirds of IllinoiSj and pecan and other hickories in the southern half of the state, add to the quality of many river-bottom squirrel habitats by helping to insure a year around food supply. The pure elm-maple type is rich in squirrel foods during the spring, but low in this respect during other seasons of the year. 492 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 acorns, nuts, buds and seeds, especially of most important wooded areas of this type elms and maples, and Osage orange fruits. are along the Mississippi, Illinois, Ohio, Water is supplied by streams and ditches Wabash, Rock, Kaskaskia, Embarrass, Big and probably by such succulent foods as Muddy and Cache rivers and aggregate berries and green corn. The fox squirrel more than 2,250,000 acres (Case & Myers Fig. 16.—The cypress or cypress-tupelo gum type in the extreme southern tip of Illinois is fair squirrel range. Foods offered by this type are cypress seeds and tupelo gum drupes. Shown here is a tupelo gum bottom, Massac County. exclusively is found in the black prairie, except in towns and in a few heavily wood- ed and ungrazed bottoms. Fig. 14 il- lustrates this type. Woodland Habitats The term woodland, as used here, de- notes squirrel habitats other than the woodlot types found on the black prairie. The Illinois woodland habitats contain a vastly larger total wooded area, as well as much larger wooded tracts, than the black prairie. A rough distinction be- tween the two types of squirrel habitat is that black prairie woodlots are surrounded by fields, while woodland range is only irregularly broken by cultivated fields or other open land. Woodland habitats, for convenience, may be divided into two main subtypes : the river bluffs and bottoms and the wooded upland. River BluflFs and Bottoms.—Con- stituting this type are the bottoms and contiguous bluffs of the various river sys- tems bordering and within Illinois. The 1934). The variety of trees and shrubs on this extensive area is great. The prin- cipal bottomland trees in the northern half of the state are elms and maples, and in the southern half these species plus oak, hickory and pecan ; cypress and tupelo gum swamps are found in a few wet bottoms in extreme southern Illinois. The bluffs in all cases support oaks and hickories, with walnut occurring in many localities. Shrubs are of wide variety and may be con- sidered an important part of the cover. A bottomland habitat in central Illinois is illustrated in fig. 15. A southern Illi- nois habitat, principally tupelo gum, is shown in fig. 16. The river bluffs and bottoms type is found in Illinois in varying densities and stages of maturity. Grazing is the rule, as in black prairie woodlots, but not many of the bottomland areas are seriously in- jured as squirrel range by this practice. Den trees are generally ample, but ex- tensive lumbering is now seriously re- ducing both the number of den trees and the number of areas containing such trees. , September, 1945 Brown & Yeager: Squirrels in Illinois 493 Staple foods, in probable order of impor- tance, are acorns, nuts, buds and seeds (especially of elms and maples), and corn. Water is amply supplied by streams, lakes and springs. Both fox and gray squirrels are common in this habitat, but the latter are much more restricted than the former in distribution. Wooded Upland.—The wooded up- land possesses many of the qualities of the river bluffs and bottoms type, but contains a larger percentage of oak, hickory, and, in northwestern, central and southwestern lo- calities, of walnut. Fruit-bearing shrubs, wild grapes, bittersweet and brambles sup- plement the basic food supply of nuts and acorns. Many of the wooded areas bor- der fields of corn, which thus becomes available as staple food, fig. 17. From the standpoint of food, the wooded upland type affords a habitat of higher quality than does the river bluffs and bottoms type, except perhaps in those bottomland situations in which pecans are plentiful. Den trees are not so abundant on the wooded uplands as on the bottoms and bluffs, due both to the presence of large numbers of hickories and other species not given to formation of cavities and to the fact that upland stands have been more con- tinuously and selectively logged, especially of oaks. The residual upland stands, as a result, are younger and more vigorous. Despite this condition there is no pressing Fig. 17.—Good squirrel country in Effingham County. Oak-hickory woods adjacent to corn- fields constitute a habitat with a dependable year around food supply for fox and gray squirrels. 494 Illinois Natural History Survey Bulletin Vol.23, Art. 5 Fig. 18.—Oak-hickory type in Piatt County, a high quality fox squirrel habitat. Here various tree species provide food through most of the year. September, 1945 Brown & Yeager: Squirrels in Illinois 495 den shortage on the wooded uplands. Water is not so plentiful, but in most up- land areas is amply supplied by small runs and springs. Grazing is heavier than on the more rugged bluffs. Fire offers a somewhat greater hazard. The cutting of walnut for military use has been more widespread and intensive on the wooded uplands than in any other squirrel habitat in Illinois. The w'ooded upland type reaches its best development in several southern and southwestern counties, but there is an ap- preciable acreage of it in Jo Daviess, Car- roll and other northw'estern counties. The extensive black oak stands in Mason and Cass counties may be considered a part of the wooded upland type. The aggregate wooded upland acreage is roughly twice that of the river bluffs and bottoms, or about 4,500,000 acres. Both fox and gray squirrels inhabit the upland type, the for- mer occurring throughout, and the latter, as in the case of the river bottoms and bluffs, being restricted generally to areas having heavy forest cover. Wooded up- land habitats are shown in figs. 18 and 19. Miscellaneous Habitats Throughout Illinois there are habitat types other than those described where squirrels occur in varying numbers. The most common are residence districts of cities and villages, parks, estates, ceme- teries and college campuses. There may be some question as to whether urban- dwelling animals are comparable to wild or non-urban populations. Observations by the writers indicate that wild and urban squirrels have identical breeding periods and great similarity in feeding and nesting habits. It is estimated that the adjoining cities of Champaign and Urbana, with a total human population of about 40,000, have 1,000 squirrels, all of which are gray. It is probable that no Illinois municipality is without a squirrel population, and that Fig. 19.—Dense oak-hickory-hard maple type, Coles Coiinty, unpastured and undamaged by fire. A typical and high quality range for both fox and gray squirrels. 496 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 200,000 or more squirrels are resident in municipal areas in the state. Stripmines, which provide an unimpor- tant habitat in the state, are best repre- sented in Vermilion, Perry, Saline and Fulton counties (Yeager 1942), fig. 20. Only in Vermilion County has forest suc- cession in this type of habitat advanced far enough to attract gray squirrels. The cover usually found in stripmine areas is an early stage of river-bottom forest, consisting mainly of Cottonwood, syca- more, willows, elms and maples, a com- bination low in quality as all-year range. Buds, flowers and seeds of trees, and fruits of brambles and wild strawberries offer an appreciable amount of spring and summer forage. Hickory nuts and acorns are seldom represented in these stands. Probably not more than a few hundred squirrels, most of which are fox squirrels, are resident on Illinois stripped lands. FOODS AND FEEDING In this investigation no study of squir- rel foods based on detailed laboratory anal- ysis of stomach contents was attempted. Through 2 years of field work, however, every opportunity to observe and record squirrel feeding was utilized. Many as- pects of the study—particularly those as- sociated with collecting specimens, trap- ping live animals and making inspections of den boxes—were well adapted to the making of reliable observations. In 716 hours devoted to hunting, several hundred records on squirrel feeding were gathered. Although the nature of the data precludes quantitative evaluation, the writers be- lieve that a good general picture of feed- ing, based on frequency of observation, was obtained. In the following discussion, as well as in table 22, no food is listed unless squirrels were observed eating it, or unless other positive evidence of its having been eaten was obtained. Food remains of squirrels were easily distinguished from those of other rodents by the location of "cuttings" as well as by incisor marks on them (Pearce 1938). Only fresh material was used in these determinations. It was im- practical to distinguish between fox and gray squirrel food remains, and for this reason, as well as because of great similar- ity in food habitats, this section of our re- port is, in general, applicable to both spe- Fig. 20.—Stripmines, lacking in trees bearing acorns and nuts, are poor year around squir- rel habitats. Vermilion County. September, 1945 Brown & Yeager: Squirrels ix Illinois 497 v^ ^If. \' I .»-*«^"Wi" i)«,m Fifj. 21.— This Piatt County woodlot of mixed hardwoods, including hickory, black oak, white oak, walnut, elm and soft maple, offers staple foods at all seasons. A nearby cornfield and an Osage orange hedge supplement this food supply. The mature trees contain an ample number of cavities. These characteristics probably represent the optimum in fox squirrel habitat. cics. Information peculiar to either spe- cies is detailed separately. Food Sources In table 22, 76 species or groups of squirrel food plants are tabulated. In- cluded are 56 trees and shrubs, 2 groups of vines, 4 brambles, 6 wild herbs, 7 cul- tivated crops and various fungi. The list is, of course, incomplete; the writers are certain that other plants, particularly herbs, are taken in small amounts. The unlisted foods, however, are of little sig- nificance in the squirrel dietary. Although many items are listed in table 22, the important staple food sources of Illinois squirrels comprise only a half dozen plant groups. There are the hick- ories, including pecan, and the oaks, wal- nuts, elms, mulberry and field corn. An imposing list of other foods ma\' be im- portant locally or seasonally. E.xamples are Osage orange and wild grapes. Boul- ware ( 1941 ) reported local use of eucalyp- tus by fox squirrels in California, and Dambach (1942) similar use of hawthorn {Cratae(/us mollis) by gra\' squirrels in Ohio. Woods (1941) reported that a blackberry patch, wild plum thicket or cul- tivated orchard may furnish the bulk of the food for one or a few squirrels during the few weeks when fruits of such plantings are available. However, no matter how varied and abundant auxiliary seasonal foods may be, most wild squirrels arc forced to rely for much of the year on one or more of the staples listed. An environ- ment without a \ ariety of staples may be of little value, and may actually be uninhab- itable, except when auxiliary foods prevail. Common examples of such a deficient en- vironment are river-bottom forests of pure elm-maple or extensive cottonwood-willow flats, even those bordering cornfields. From the standpoint of food, the impor- tance of mixed stands in squirrel habitats is clearly apparent, fig. 21. I his factor is discussed by Goodrum (1938). Most of the original forests were of suitable composition, especially those of hardwoods or mixtures of hardwoods and conifers. Most of the larger natural stands now- present in Illinois meet the staple food 498 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 0. 2 u. rt < I o c Ml p < UJ c/-, 00 ,^ ^ oo ,^ ^ CA. < j^ GO c/} or. < ^ < < cyo < < < < < CAl c/) Q u O H ;^XXXXXV^! 4-' 0000 c o c i- ^ ^ en en C 3 C C D 3 HJ OJ OJ _Q -Q *^ p p ''^ T ? 3 (LI OJ g> a ^ ^ •^ I £ E OJ Oj a. ci. CJ OJ 00 hi 3 brj 3 < 3 3 < 3 bfj 3 O -^ o o -a c rt rt tn SSS -a c D r3 00 ^ -t3 -d c c rt rt >. >^ J- T3 t3 C C rt rt dj < < rt rt rt 7i < < C
  • Ci, rt Oj -i:; J::j CA. :§sssssss -d ns xj c c c rt rt K -T3 C -T3 rt C_ rt < < < (U U OJ ^- ^- -tJ rt rt rt J hJ -1 < < a u ^ 3 J to *r- *-( ~ rr r::: a a a < < < -t3 Td -T3 c c c rt rt rt JS ^ J= o u o tJ CD .£ o ="_ i: bfj Jii "2 o1 £ 2 Q •- O fc £ >. o T3 -O > > O O E o 4-« t^ -r-l C/3 O O C P . ^^ Ix Ui . ,— , ^ .-2 .-5 ^ o o P ^ I -a p re O. — ' ^ j^ jj re o [i( O c^o < O /^. Q p o o 4-1 +-» p *-< ' 2 * n 3 3 .5 • = D •^ h o _Q J3 (^ S S TS 5J U C ^ 2 a = '-> ^ ^1 -a I t« C S ^- « S S3 «i g 3 g- U < C^ Q 3 0! u CO c CO 3 '3 '3 '3 "3 3 3 '3 ^ u '3 t3 3 .5 c o ca a Q Z <: CO U U R •2 .5 'So •^ -s S; « 2 .S o „ a. •^ ;5 •5 « CLi CL, ^ CO 5 o ''^ K < •4i o r Ml CO o o -a &. >> -a S « R o :^ I R R ~R v> R a, v> I ^ ^ b "5 " I -3 ti -d >. September, 1945 Brown & Yeager: Squirrels in Illinois 501 3 c o U 03 « o u c 3 ^ cH c^ < W C/} CA) < W V. <<<<<<<< o: ^ J^ _ o O H O 5 O Q O i-i ct U C a o 6 o I t3 -a ^ T3 Y ^ c c c c i "3 rt o ^ •- J*' 2 S "I -S ^ -2 S Q E OJ 1 lU O o -a s »- Q 3 C .1 T 3 OJ 3 i
  • . -^ O -3 aj 3 Qj Jr' E a c/: O O JO .T) o o Q (I) N E- < u c :::::::: -a .'.: \ '.'.'.'.'.'.'.'. '. c rt >H J2 ,. J2 j£ : « : ^ .jihjSCQcAJC/icAicriCQc/Dc/jc/jc/:; eg b! Id a: N cu O U S 2 5 ^ ^' -if R <2 R -. I' u 3 to -i: O J. CI ^ 0:: c^ CQ « 3 502 Illinois Natural History Survey Bulletin Fol. 23, Art. 5 requirements of both fox and gray squir- rels, and many woodlots, supplemented by agricultural crops, particularly corn, meet these requirements for fox squirrels. The writers found during 2 years of field work only one extensive squirrel habitat showing definite evidence of food shortage. This was the Mississippi River bottoms in Carroll County, where pin oaks furnished the main squirrel fare over a large area. Only fox squirrels occurred there, and they were somewhat under- weight, mangy and otherwise in subnormal condition during the late winter of 1940- 41. The near failure of pin oak acorns on the area in 1940 is believed to have been the main reason for this situation. At least one other area was found where serious food deficiency would likely result from mast failure. This was the sand region of Cass and Mason counties, where extensive and nearly pure stands of black Fig. 22.—Nearly pure black oak stand in Mason County, Illinois. During years of mast failure, pronounced squirrel food shortage may exist in this type due to lack of variety in staple food species. Den boxes, erected for wood ducks, are readily used by fox squirrels. September, 1945 Brown & Yeager: Squirrels ix Illinois 503 Fig. 23.—Elm (left) and maple buds and flowers offer the first squirrel food jiroduced each year. oak occurred, fig. 22. Only fox squirrels inhabited this locality, and during years of poor acorn crops they would be forced to depend mainly on residues of corn, rye and other grains, and such natural foods as wild grapes, bittersweet and miscel- laneous seeds and herbage. In practically every section of Illinois, a general failure of oak mast, and in some sections, especially in southern and south- w'estern localities, failure of wild pecans in the bottoms and hickories and black walnuts on the uplands might create un- fortunate food contingencies during the late winter and early spring. That serious food shortages did not prevail in many in- stances in 1940—1942 is indicated by the good to excellent condition of the several hundred squirrels examined, some of which were collected during every month of the first 2 years of study. The nature of the food studies made in this investigation did not permit deter- mination of either the number or impor- tance of animal foods taken by squirrels in Illinois. Numerous writers, however, have called attention to the inclusion of insects and other animal forms in the dietary. Davis (1907. 1924) reported the destruction of acorn weevil larvae {Balaninus) and oak apple galls {Ain- phibolips confluens) by gray squirrels. These animals were observed by Hamilton ( 1943) to feed on caterpillars of the half- wing geometer {Phiyalia titea). Good- rum (1940) found that in Texas over 3.5 per cent of the food of gray squirrels con- sisted of insects, mainly lepidopterous lar- vae. He also presented limited evidence to show that animal food is necessary to successful breeding. Both fox and gray squirrels are said by Seton (1928) to use insects and other animal matter. The evidence is general that animal life, par- ticularly insects, constitutes a small but more or less important food source for tree squirrels. Brooks (1922) reported the use of chestnut bark and other tree bark by gray squirrels in West Virginia, and Allen ( 1943) reported use of maple bark by fox squirrels in Michigan. 'I'he use of bark by fox squirrels was observed by the junior author in Coles County, Illinois. The effect of lumbering, fire and graz- ing on squirrel food sources is discussed in other sections. Food Succession Succession in the use of foods by squir- rels is somewhat distinct, the Illinois study showed, and the order of succession in this state is approximately the same in both species. The first foods of the late winter or spring season are the buds and flowers 504 Illinois Natural History Survey Bulletin Vol.23. Art. 5: of several hardwoods, particularly of elms, maples and oaks, and the buds of sweet gum, ash and other tree species, fig. 23. "Budding," well described in gray squir- rels by Nichols (1927), Deuber (1934) and Terres (1939), begins in February in probably other acorns may be as early as July 15 in Illinois, most mast species are not used extensively until about mid August. Fruits of oaks, sugar maple and honey locust are commonly eaten in August and later, and are followed by Fig, 24.—Corn cribs or corn shocks or fields adjacent to squirrel range offer the best feeding stations, and may carry normal squirrel populations through severe food shortages. Pike County. southern Illinois and extends into April. During late April and May, the winged seeds of the American elm are an impor- tant item, in the diet of Illinois squirrels. From mid May until late July mulberries are utilized in all regions where they oc- cur. Various bramble fruits, as well as wild cherries, wild grapes, wild strawber- ries and wild plums, are eaten during the summer and early fall as they become available. Corn, in the milk stage, is eagerly sought by both species during July and August, but is much more important to fox squirrels than to gray squirrels be- cause of the wide occurrence of the former in open, agricultural range. Fungi and herbage are taken probably in maxi- mum quantities during the spring and summer ; ground feeding, in which fungi and herbage are mainly found, is most prevalent in July and August. It is dur- ing this period of extensive ground feeding that squirrels are most difficult to see in the woods. In Illinois, July and August usher in the principal mast season, the period of greatest food abundance for tree squirrels throughout the northern hemisphere. Although initial use of black oak and nuts of the hickories and walnuts. Pecans, beechnuts, hazelnuts, fall grapes, Osage orange fruits, pokeberries, ripe corn and numerous other foods are generally used in late August or September and later. In the extreme southern tip of the state, the seeds of cypress and tupelo gum are appre- ciable food items in late October. Al- though rare in Illinois, the seeds of various pines are a staple fox squirrel food wher- ever the range of the trees and the animal coincide. Following the flush of mast availability in September and October, acorns and nuts supply the bulk of squirrel food during the winter and early spring. Such food is taken both from residues on the ground and from cached supplies. It is after these sources are largely used up, and be- fore the availability of buds, that the food problem of squirrels most often becomes acute. In many farm localities, corn, whether residue, shocked or cribbed, is of great value during this period of deficiency, fig- 24 ; other emergency foods consist of Osage orange fruits, often dug out of snow, still clinging box-elder seeds, dried grapes, frozen, half-decayed apples and such miscellaneous items as smartweed, September, 1945 Brown & Yeager: Squirrels in Illinois 505 climbing buckwheat, burdock and Ameri- can lotus seeds. In several instances it was found that acorns that had fallen in water were eaten 3 or 4 months later, after the winter drawdown, on areas af- fected by navigation dams on the Missis- sippi River, fig. 25. Many other seeds are undoubtedly eaten during the period of scarcity ; and various writers have reported greater use of animal foods, particularly insects, during the late winter and spring than at any other time. Food Preferences The acorns of every species of oak oc- curring in Illinois appear to be used by squirrels, but because of their abundance and wide distribution those of pin oak {Quercus palustris) , white oak {Q. alba) and black oak {Q. velutina) are the most important food sources. The acorns of bur oak {Q. macrocarpa), shingle oak {Q. imbricaria) , chinquapin oak {Q. Muhlenbergii) , swamp white oak {Q. bicolor) and others are taken where they occur. According to Allen (1943) red oak {Q. borealis maxima) acorns are bitter and, in Michigan at least, appear to be used less than the fruit of most oaks. Of the hickories, the shagbark (Carya ovata) , both because of its statewide dis- tribution and tendency to fruit, is easily first in use among Illinois squirrels. Nuts of the small pignut (C. oralis), occurring most commonly in east-central and south- ern Illinois, were found to be eaten avidly by both fox and gray squirrels, fig. 26. The mockernut (C. alba), pignut (C. glabra), big shellbark (C laciniosa) and most other Illinois hickories are of only secondary importance, partly because they are less common than the shagbark and also, perhaps, because they are thicker shelled and therefore more difficult for squirrels to open than are the thin-shelled species. The bitternut {C. cordiformis) , although thin-shelled, is both bitter in taste and small in size, but appears to be uti- lized. Pecan (C. pecan) is eagerly taken wherever it occurs and represents the most important mast species in the central and lower Illinois River bottomlands and in some southern Illinois localities. Squirrels show definite preferences when several foods are abundant at one time. During "mast years," when a dozen or more staple or substaple foods, including hickory nuts, walnuts, pecans, acorns, beechnuts, hazelnuts and corn, may be available in quantity from late August through September, hickory nuts (shag- bark and the small pignut) seem to rank first in preference with both fox and gray Fig. 25.—After winter drawdown on area affected by Mississippi River navigation dam, squirrels foraged under ice for pin oak acorns that had lain in water since the previous fall. Carroll County, January, 1941. 506 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 squirrels. While these nuts are available, squirrels travel greater distances for them than for any other food and lose to a greater degree their altertness to danger when feeding on them. Pecans and black walnuts also rank high. Among fox squirrels living in farm habitats where nuts are absent, the fruit of the Osage orange seems to rank next to corn as a preferred food, and in numerous instances was taken in winter, even when acorns were available, fig. 27. In the early spring, elm buds and seeds are the most used foods of both squirrel species ; in May Fig. 26.—Two hickory trees, heavily fruited, known to have supplied niuch of the food of 3 20 or more Coles County squirrels (both fox and gray) from late August until late September in 1943. September, 1945 Browx & Yeager: Squirrels ix Illinois 507 Fig. 27.—Osage orange fruits provide food for fox squirrels from late summer through the winter. Cobs under the tree indicate extensive use of corn from an adjoining field. and June, mulberries apparently rank first; and, during the early summer, corn in the milk stage is probably highest in palatability rating, at least for fox squir- rels. Because of the well-known adaptability of fox squirrels to open timber and agri- cultural habitats, this species makes greater use of farm crops than gray squirrels. Of farm-crop foods, corn is of outstanding importance, but wheat, soybeans, oats, apples and other crops are popular. Field crops adjoining woodlots or other timbered areas are used more than those in fields some distance from such areas. Corn is the only cultivated crop used to any con- siderable extent by gray squirrels in Illi- nois, and this only where fields adjoin woodland suitable to their requirements. Isolated nut trees, hazel clumps or bramble patches are ordinarily monopolized by fox squirrels. Failure of any important mast species tends to hasten and increase the use of the species that produce. In 1941, the hick- ory nut crop was heavy over much of Illinois. Squirrels in the central zone began to use the nuts by mid August, and black walnuts were left untouched until early September. In 1942, hickory mast was scarce in many localities. The small supply was soon exhausted, and in August the squirrels shifted to walnuts, which were still green. Squirrels inhabiting areas short of summer foods, of which heavily grazed woodland is probably the best Illinois example, are often driven to use immature acorns. In the black oak stands in Mason and Cass counties, where the ground cover is mainly grasses, seed- lings and second-growth sprouts, immature acorns were taken by the fox squirrels resi- dent there as early as July 15. Fox squirrels were found to be more tolerant of limited variety in diet than gray squirrels, and on many areas having only one or a very few staple foods it was Fig. 28.—Svveetgum "hails" stored by a gray squirrel, Horse Shoe Lake (Jame Refuge, Al- exander County, Illinois, December, 1940. This is the only instance of cavity storage noted in tree squirrels in 4 years of field work. 508 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 noted that the squirrel population was lim- ited to the former species. This situation was encountered on certain Mississippi River bottoms where pin oaks supply the main food resource; in the sand region of Mason and Cass counties, where black oak supplies the main food staple ; and on farm regions throughout the state, where corn is the basis of subsistence. Food, however, is only one criterion for defining the pre- ferred range of the two species. The range appears to be determined by the combination of food, cover, water and pos- sibly space. In the course of field work it was noted many times that both species of squirrels, even in regions abundantly supplied with food, made limited use of acorns, walnuts, hickory nuts, Osage orange fruits and similar items while they were still quite green. What this use represented—mere- ly a sampling, the activity of juvenile squirrels, an attempt to obtain water—was not ascertained. Storing and Feeding Habits Storing or caching appears to be in- stinctive in squirrels; juveniles are among the first to begin this activity in the fall. Fig. 29.—Fox squirrel feeding in characteristic manner— sitting on hind legs with nut grasped between forepaws. (Photo by Gordon S. Pearsall.) Septembetj 1945 Brown & Yeager: Squirrels in Illinois 509 Caching in Michigan fox squirrels was well described by Cahalane (1942). The stored foods observed in the present Illi- nois study were mainly hickory nuts, wal- nuts, pecans and acorns, which were com- monly buried in the ground. Only one Squirrels seem to have the ability to de- tect unsound nuts and acorns, usually fruits undeveloped or worm eaten. By what means the)- make this distinction is not known, but we have many observations of squirrels dropping unsound nuts almost 30.—"Cuttings" on the ground under a hickory tree, Coles County, September, 1943. instance of cavity storage was found : a gallon or more of sweet gum {Liquid- amhar styraciflua) capsules in the hollow base of a tree of this species, fig. 28. The cache, on the Horse Shoe Lake Game Refuge, Alexander County, was the work of a gray squirrel. In storing, squirrels usually bury only one nut or acorn in a place, carrying each to a point 50 to 100 feet from the food tree by the most direct route. Storing begins about September 1, and in both 1940 and 1941 it was noticed first in gray squirrels. It seems to be an ex- tension of the forenoon and afternoon feeding periods, and is conducted with fewer-than-usual alerts for danger. Har- vesting is rather thorough ; once cleaned, the trees are visited only infrequently. In trees nearly stripped, squirrels were ob- served to go to the uppermost branches and descend in spiral fashion until a nut was found. Acorns and nuts are gleaned later from the ground, but apparently the storing of fallen fruits does not awaken in squirrels the intensity of purpose compa- rable to that shown early in the season when stores are gathered directly from the trees. instantly after picking them up. The un- huiled nuts they dropped that were exam- ined by us usually showed only one set of incisor marks ; the hulled nuts showed little if any "cutting." In feeding, squirrels ordinarily sit up- right on their hind legs, whether on a branch, stump, log or the ground. They possess great skill in handling food with their front paws while eating, fig. 29. Gray squirrels often eat on the spot where they find food, but sometimes, as with fox squirrels usually, they carry the food to a favorite eating place, such as a horizontal branch, a log or stump. Animals of both species leave abundant signs in the form of "cuttings," figs. 30 and 31, and hunters habitually locate them by looking under hickory, walnut, pecan or oak trees to de- termine the extent and recency of feeding activity. The animals dislodge from trees more fruits than they eat but they usually eat cleanly the nuts and acorns they open. Neither fox nor gray squirrels take a large number of foods in making any one meal. The writers opened scores of stomachs, but seldom found more than four or five foods in any one stomach, and often only one or two. Items present in 510 Illinois Natural History Survey Bulletin Vol.23, Art. 5 stomachs could often be identified by odor or appearance. Minerals The mineral requirements of squirrels are not well known. Little information on the subject was gathered in this investi- gation. As reported previously (Carlson 1940, Coventry 1940), bones are eaten by squirrels were never found at any appreci- able distance from open water. Some evidence is available that mul- berries, plums and other succulent fruits serve as water sources for Illinois fox squirrels. Robert E. Hesselschwerdt of the Illinois Natural History Survey did not find that fox squirrels on the Urbana Township Wildlife Area showed a ten- dency to migrate during the extremely dry Fig. 31.—Examples of squirrel "cutting" on nuts of the small pignut, Carya ovalis. The thin hull and shell of this species, in addition to the sweet-flavored meat, make it highly at- tractive to both fox and gray squirrels. both species of squirrels, perhaps for the purpose of obtaining minerals. Baum- gartner (1939fl) reported that fox squir- rels eat soil to obtain mineral salts. Soil was found in small quantities in some of the stomachs opened by the present writers. Water Water apparently is not a requirement of the fox squirrel habitat, but it seems to be a necessity in the habitat of gray squirrels. The tracks of both species are often found in the mud or sand at the edge of streams, ponds and lakes. It was not determined in the present study how often squirrels drink, but observations on ani- mals and study of tracks indicated that during the warmer months gray squirrels, at least, take water daily. A comparison of typical habitats of the two Illinois spe- cies leads to the conclusion that the gray squirrel is more exacting in its water re- quirements than its larger cousin. Gray summer and early fall of 1940, when all open water within 2 or 3 miles had dis- appeared. During this period the squir- rels made free use of Osage orange fruits and of green corn and apples, from which sufficient moisture may have been obtained. On the Mason County area, wild grapes, blackberries and wild plums probably supplied needed moisture during periods of drought. Other observers, including Allen (1943), have noted the ability of fox squirrels to survive on uplands far from open water. Terrill (1941), work- ing in Missouri, found that extreme drought, resulting in the withering of succulent foods, tended to concentrate both fox and gray squirrels around ponds or other open water sources. _ NESTING As has been reported by many writers, fox and gray squirrels throughout their range utilize both leaf and cavity nests. I September, 1945 Brown & Yeager: Squirrels ix Illinois 511 The degree to which they use each type is determined, at least partly, by the kind and age of the trees in an area. Squirrels were sometimes found by the present writ- ers in young stands, in some cases where cavities were very scarce; but the animals were more common in older, cavity-con- taining timber. There is no doubt of the superiority of the mature forest range, but the fact that both fox and gray squirrels built leaf nests even where cavities were present suggests that the highest quality habitat must possess the possibility of both types of nest. The writers believe that either type of nest may supply the essential year around nesting requirements of either species. Dens On the large expanse of Illinois black prairie, where only the fox squirrel is im- portant, there is an acute shortage of tree cavities suitable for denning purposes. In this region, a few bottoms, occasional woodlots and Osage orange hedgerows supply the main tree cover. The hedges contain very few cavities, and Osage orange leaves are not well suited to nest construction. Although both bottoms and woodlots of the black prairie region con- tain numerous trees with cavities, the total acreage of such units is so small and their distribution so poor that great inadequacy of dens prevails in the region. In one Illinois study, Hesselschwerdt (1942) demonstrated that boxes made of lumber serve very usefully in meeting the den shortage in the fox squirrel habitat of the black prairie, fig. 32. Use of these boxes is discussed further in the section on "Management." Many river bottoms and wooded upland areas, particularly in southern parts of the state, are well supplied with den trees. Most cutover areas, as a result of the des- tructive practice of cutting to smaller diameter limits, have been stripped of big. 32.—Xesi box Miitahle tor sciiiinels in an Osage orange hedge, Champaign County, 1940. A screech owl is sitting in the entrance of the box. An acute shortage of tree cavities suitable for denning purposes exists on the Illinois black prairie. 512 Illinois Natural History Survey Bulletin Vol.23, Art. 5 «.« i^'--'^ 1 Fig. 33.—Den tree used by fox squirrels, Piatt County. Cavities are usually higher in trees than the cavity shown here. This den tree is included in the habitat illustrated in fig. 21. September, 1945 Brown & Yeager: Squirrels ik Illinois 513 trees with cavities. Selective cutting, es- pecially if light, results in little harm to squirrel range, either temporary or per- manent. The best den trees in Illinois are the oaks, maples, American elm, white ash, beech, sweet gum and, in extreme southern Illinois, cypress and tupelo gum. The in- herent soundness of such trees as Osage orange, Cottonwood and the hickories, even when mature, eliminates them as impor- tant den producers. The oaks, partly be- cause of their abundance and state-wide range, are easily the most important den- tree group, fig. 33. The physical characteristics of cavities in relation to squirrel denning require- ments were not studied h\ the present writers. Baumgartner (1939/>') and Allen (1942, 1943) reported in some detail on this subject. Both writers found that squirrels maintain den entrances at a suitable size in growing trees by gnawing the green cambium each year. Allen (1943) found that fox squirrels used al- most any size or depth of hollow, some- times stuffing with leaves those too large for comfort. He also found that certain individuals may establish and use specific dens for long periods, occasionally for the entire life of the animal. Four or i\vt usable cavities per acre are probably ample for any permanent squirrel population. The present writers found considerable evidence that one squirrel, male or female, may use concurrently two or more cavities or nest boxes. Of the protective value of cavity nests, Allen (1942) aptly states: 'Trom the management standpoint, hollow trees are doubtless desirable even though squirrels can live without them. They protect the animals from hunters, natural enemies, such as raccoons and owls, and severe weather." The present writers, in agree- ment with Allen, have observed that good tree cavities afford, during storms and ex- treme cold, a protection that may be Fig. 34.—Typical fox squirrel leaf nest in oak, Cook County. (Photo by Gordon S. Pearsall. 514 Illinois Natural History Survey Bulletin Vol.23, An. 5 Fig. 35.—Fox squirrel nest in white oak tree, Piatt County. Leaf nests may be located in almost any position or height in trees, but most commonly they are situated in branch crotches near the central stem and at heights lower than shown here. September, 1945 Brown & Yeager: Squirrels in Illinois 515 largely responsible for high survival rates of juveniles and of adults in winter. Leaf Nests Late summer is the period of greatest nest-building activity in Illinois for both fox and gray squirrels. Stoddard (1Q20) indicated that the fox squirrel in Indiana and Wisconsin constructs two types of leaf nests, a compact one used for young-rear- ing, and a larger, more loosely constructed nest used as a summer retreat. Wide variability in the size and shape of nests, in construction materials, and position in trees was observed in the present study. This variabilitv rendered classifving and aging of nests so difficult that the writers were unable to use them as a satisfactory means for censusing squirrels, although a general correlation seemed to exist between the number of nests and the size of the population. Squirrels in Illinois were found by the writers to exhibit no clearly defined choice of tree species for nest building. Perhaps because they were the most abundant and widely distributed tree group, oaks con- Fig. 36.—Box elder barked by fox squirrel, Ugie Lounty. (Photo by C. S. Walters.) 516 Illinois Natural History Survey Bulletin rol. 23, Art. 5 tained the largest number of nests. Oak leaves were the most widely used nest material, partly because of abundance, but also, the writers believe, because oak leaves and twigs are highly suited to the type of construction found in squirrel nests, fig. 34. Nests were found in every common Illinois tree species, including cypress and Osage orange. In most cases they were made from leaves of the host tree, but other material also was used. Thus, nests of tupelo gum leaves were found in cypress trees. Crotches of larger limbs were the most common construction sites observed, but there were many sites in forks, between slender branches and, not uncommonly, in the topmost branches of tall trees, fig. 35. Unlike the Bryant fox squirrel, as reported by Dozier & Hall (1940), nei- ther Illinois species was found to choose a characteristic nest position in trees. Ordinarily, the nests observed by the writers were not lined, but the inner leaves had become frayed and served as lining. Finely shredded bark was at times used for this purpose, and occasionally grass, fine roots, and even rags and paper had been utilized. Some individuals, particularly female fox squirrels, seemed to be addicted to the barking of trees, fig. 36, for the purpose of obtaining nest material, and no doubt for other reasons. The use of bark in tree-cavity nests has been reported previously (Yeager 1936). HUNTING Material gathered during the course of the present investigation included infor- mation on the method of hunting squirrels in Illinois, on the annual kill and on crip- pling losses. Hunters and Hunting Methods In Illinois, no field sport except rabbit hunting is confined more to rural and small-town populations than that of squir- rel hunting. Whereas waterfowl and up- land bird shooting draws its devotees large- ly from urban and professional groups, squirrel hunting is mainly the diversion of farmers, laborers and local business men. This is true particularly in the important southern zone. The sport is highly prized by those who participate in it, both for its recreational value and because it means "meat on the table." To thousands of Illinois citizens, a "mess of young squir- rels" is a delicacy annually looked forward to ; and to some the resource represents an important and often needed food during the late summer and early fall, fig. 37. Squirrel hunting tactics are very simple. With experienced hunters, no form of hunting is more likely to result in game bagged, because an understanding of squir- rel habits practically insures success. If persistently hunted, however, both fox and gray squirrels become wary, and under such conditions stalking them requires a considerable degree of skill. Squirrel hunting, except when a dog is used, is primarily a stalking and waiting game. During the mast season, one of the most successful methods is for the hunter to sit or stand quietly near hickory, walnut or oak trees currently being "worked" by squirrels. Often hunters reach such feed- ing sites by daybreak and shoot the animals as or soon after they emerge from nests in the vicinity, or approach from outlying territory. Under such conditions the killing of one squirrel does not result in cessation of feeding by other squirrels for more than a short time, often only a few minutes. Indeed, limits of five squirrels are often killed at a single site, and some- times from a single tree. The writers have several records of five squirrels killed from one tree in the space of a few min- utes. In such cases, the hunters shot the feeding animals before they could escape into surrounding cover. It is not uncom- mon for bags made under such conditions to be composed of both fox and gray squir- rels. Stalking is a favorite method of hunting when conditions permit. During dry pe- riods, leaves and twigs are noisy when walked upon, making stalking difficult or impossible. When such conditions pre- vail, hunters advance from point to point, remaining quietly for a time at each. Points that offer a good view of the sur- rounding territory are usually selected. Thus, the end of a ridge, especially when bordered by a narrow valley and with tim- bered slopes beyond, offers a favorable waiting site. When quiet stalking is pos- sible, such as after a rain or early in the morning, hunters walk slowly through the woods, either overland or along trails, pasture fences or dry creek beds, taking September 1945 Brown & Yeager: Squirrels in Illinois 517 advantage of all cover en route. This method permits maximum coverage of hunting territory. A summary of hunt- ing success of 236 Illinois hunters in 1940 and 1941 is given in table 23. Dogs, which are not widel\ used in squirrel hunting in Illinois, are perhaps most common in the southern zone; they are most effective after the leaf fall, when squirrels can be easily seen. The 1944 season, closing November 15, October 30 and October 15, in the northern, central and southern zones, respectively, when leaves were still on the trees, virtually eliminated the use of dogs in the soutiiern zone, and permitted only limited use in the ::J Fig. 37.—A limit typical for central or southern Illinois—three gray and two fox hiitguns are used by many Illinois s(juirrel hunters. squirrels. 518 Illinois Natural History Survey Bulletin Vol 23, Art. 5 central and northern zones. It is said that squirrel dogs were more widely used in Illinois when the season closed later than in 1944. The writers believe that the data pre- sented in table 23 are too few and selective to be accepted at their face value. There is reason to suspect that they are based on returns made by the more successful hunters. The strikingly uniform bag of slightly more than one squirrel per hour in all zones and for both years represents a very high index of hunting success. The writers suspect that the true index of suc- cess falls between 0.5 and 1.0 squirrel bagged per hour. The uniformity in success per unit of effort in the three zones may be explained by the relationship that exists between the number of hunters and the number of squirrels in each zone. Just as there is a progressive decline in the acreage of squir- rel range, and consequently in squirrel numbers, south to north, there is likewise a decline in the number of squirrel hunt- ers. This circumstance would make for more or less equal hunting pressure and consequently success, as is indicated by the data. It is not known how accurately crip- pling losses are indicated in table 23. On the basis of the writers' observations and the opinions of many experienced hunters, the figures are conservative. The great- est source of error probably lies in the number of animals hit but giving no indi- cation to hunters of having been wounded. Such cases are not listed in the tabula- tions. There is evidence based on skulls and bones found in tree cavities that an appreciable number of wounded squirrels reach their dens and die there. The habit of shooting into leaf nests is more or less common in Illinois. Allen (1940, 1943) in Michigan has shown this to be a wasteful and altogether undesirable Table 23.—Average number of squirrels bagged, hours of hunting, squirrels bagged per hour and crippling losses, as reported by 236 Illinois hunters, 1940 and 1941. Zone Number OF Hunters Reporting Average Number Squirrels Bagg&d per Hunter per Year Hours ot Hunting per Hunter per Year Squirrels Bagged per Hour Cripples Not Bagged* (Per Cent of Total Known to Have Been Hit) Fox Squirrel Gray Squirrel 1940 Northern, Central. . Southern . Total or Average 18 30 110 158 14.8 18.4 19.7 18.9 13.2 16.7 17.9 //./ 1.2 1.1 1.1 1.1 8.1 12.6 12.6 12.0 10.5 12.8 15.7 15A 1941 Northern Central .... September, 1945 Browx ^' Ye.ager: Squirrels ix Illinois 519 practice. He found that the majority of leaf nests shot into did not harbor squir- rels, and in instances where animals were present they usually did not jump from the nests if hit ; if they were killed, he believed they usualh' were not recovered. The types of guns used by Illinois squir- rel hunters are indicated in table 24, which is based on 158 returned questionnaires. A carving, fig. 38, by an unknown in- dividual is indicative of public interest in .squirrels. Kill Through the cooperation of the Illinois Department of Conservation, a good esti- mate of the 1942 squirrel kill in Illinois, based on hunters' kill return cards, is available. The total was 1,463,305 squirrels. A breakdown of the 1942 kill, as disclosed by the present investigation, is presented in table 25. We have no com- parable data for 1940 and 1941, the hunt- ing seasons principally represented in this study. Table 24.—Types of firearms used by 158 Illinois squirrel hunters reporting in 1940. ':'. / Tv'i'E OF Firearm 520 Illinois Natural History Survey Bulletin Vol. 23, Art.5\ sent between 1 million and VA million pounds of edible game. MANAGEMENT Management of wildlife resources is basically the maintenance of various spe- cies at any desired population level. To accomplish this objective, use is made of what is known of the life requirements of each species in question. Thus, in the field, pheasants may be provided with more ade- quate winter cover, or quails with brush- bramble thickets adjacent to food areas. If such changes plug the most serious en- vironmental gaps confronting the species, the habitat is improved ; and, in the broad sense, further improvement is attained only when the next most serious gap has been mended. It can be said that game habitats are no better than their weakest environ- mental factor, and that they usually may be improved up to the point where all conditions are optimum, after which intra- specific tolerance, or lack of it, becomes the important factor in population density. Our present knowledge of squirrel ecol- ogy, admittedly inadequate, permits some general suggestions for managing fox and gray squirrels in Illinois. Habitat Improvement Among the more effective means of im- proving squirrel habitats are maintaining favorable food and den tree combinations •through selective cutting and planting, maintaining hedgerows, providing den boxes, protecting against fire and grazing, and supplying feed in winter. Forestry Practices.—In that fox and gray squirrels are dependent on woodland, no factor can be more important in their husbandry than the woodland management policy. Fortunately, good forest practices generally lend themselves to good squirrel management, especially in the case of fox squirrels. In fact, a small amount of cutting improves large, unbroken stands as squirrel range, because the openings so made promote the growth of food-produc- ing brambles and shrubs, and hence greater variety in both cover and food resources. Fox squirrels may respond to improve- ments effected by selective cutting within a year or two; gray squirrels only after appreciable shrub growth has appeared. Shrub-bordered woodlots or stands provide] variety in food resources, and the shrubs are of value in site protection. Logs and down treetops, or piled brush, have a cer- tain, but unmeasured, attractiveness for squirrels, and their presence in the habitat adds to its quality. Slashing, wherein all commercial timber is ruthlessly cut and logged, may—and indeed often does—destroy completely a woodland as a squirrel range. Such cut- ting, followed by fire, may eliminate oc- cupancy even by fox squirrels for 10 to 25 years. Likewise, the cutting of all defective trees, to which cavity dens are largely confined, greatly reduces habitat quality, not only for squirrels but for other cavity-denning wildlife. Many de- fective trees are good mast producers. Release and improvement cuttings that result in taking out all or most individuals of such species as mulberry, black cherry, wild plum, hawthorn and wild grape make for food shortage during the spring and summer. It has been observed that one elm and one mulberry per acre in oak- hickory or beech-maple types may represent the difference between good, permanent habitat and that which is deficient for squirrels during the spring and early summer months. The usefulness of mul- berry is noted by Goodrum (1938). Naturalness in forest stands, involving a reasonable variety of species, the presence of all age classes, including some defective, cavity-containing trees, and an understory of shrubs and young trees, insures a satis- factory squirrel habitat in almost any part of Illinois, fig. 39. Forest practices that result in leaving at least a few oaks, hickories and walnuts in the stand are of the greatest importance in maintaining the squirrel range. Of these three tree groups, the hickories, including the pecan, are, tree for tree, of the greatest value to squirrels. Hickories are gen- erally considered of secondary commercial value for lumber, and a policy of favor- ing them in forest practices creates a con-j flict of interests. However, where hickorj constitutes an appreciable part of the stand, as it does throughout much of the oak-hickory type, it is not necessary tc save every hickory in maintaining gooc squirrel range. Under -such circumstances^ release and improvement cuttings mar well favor the commercially more valuable September, l'J45 Brown & Yeagkr: Squirrels in Illinois 521 oaks, walnuts and yellow poplar, reserving and timbered areas. Many of the scat- only a few hickories per acre. tered Osage orange trees occurring in Stand composition in high quality squir- Illinois pastures and woodlots are believed rel range must, however, consist of more to have originated in this manner. Squir- than acorn and nut species, notwithstand- rels are probably responsible for others. Fig. 39.—Mixed hardwood stand, Piatt County. This forest type, common in Illinois, offers one of the best year around habitats for squirrels. ing the essential function of these groups in producing food staples. Spring and summer food species are needed, since mast is not available until midsummer or later. Highly important are buds and seeds of elms and maples, the first green food of the \'ear; mulberries, which tend to replace buds and seeds in the diet in May and which supply a staple food throughout July ; and black cherries, wnld plums, serviceberries and similar fruits, all of which become available in summer. The mulberry is especially useful be- cause it not only offers an attractive food during a food-deficient period, but is shade tolerant and grows and produces well un- der a variety of site conditions. It appears to do best on moist, fertile, riverbottom soils. Osage orange trees in woodlots or other forested areas provide a good food re- source. Cattle ma\- eat Osage orange fruits during the winter and thus scatter viable seeds in droppings over woodlots Brambles, particularly blackberries and raspberries, improve the food resources of any squirrel habitat, as does adjacent corn. Hedgerows and Fencerows.—In farm localities, or in an\' region where woodland occupies only a small acreage, hedgerows and fencerows may constitute a very appreciable part of the squirrel habitat (Whitaker 1939). Even in more heavily wooded localities, hedgerows con- necting two woodlots or stands, or offering shelter along cornfields or bramble patches, represent a valuable feature of the range. The most common black prairie squirrel habitat is the Osage orange-corn- soybean combination, supplemented in some cases by food- and cavity-bearing walnuts, oaks and maples, usually near a farmstead. Although of very low carrying capacity for the total acreage involved, this type of habitat is in some respects satisfactory for fox squirrels, as is attested by the generally e.xcellent condition of animals collected in 522 Illinois Natural History Survey Bulletin Vol. 23, Art. it. Removal of hedgerows, which has been extensive during recent years, has measurablj' reduced the acreage of habit- able fox squirrel range in the state. Undoubtedly the best hedgerow cover for squirrels is offered by very large, un- trimmed Osage orange trees, but a hedge of this size lowers the crop yield for a distance of 20 or 30 feet on each side and therefore is resented, with some justifi- cation, by many landowners. Smaller hedgerows are of material value to fox squirrels, and trimming, although it im- pairs, does not destroy their usefulness to squirrels. Fencerows of oaks, elms, maples, hickories or red cedars are com- monly used by fox squirrels to the limit of food and cover offered. The value, to fox squirrels particularly, of one or a few good food trees in hedge- rows, corners or in open stands is appre- ciable. The most desirable species for such situations are hickories, including pecans, walnuts and most oaks. They are well adapted to hedgerow planting, as they produce well when isolated and thus fa- vored by full light. Den Boxes.—Den boxes, fig. 40, suit- able for squirrels and other cavity nesting species have been tested extensively in Illinois (Hawkins & Bellrose 1941, Hes- selschwerdt 1942, Yeager 1942, Brown & Bellrose 1943) and in Michigan (Allen 1942, 1943). The outcome of these studies leaves little doubt of the possibility of substituting artificial for natural cavi- ties in regions where the latter are scarce or lacking. Den boxes appear to be es- pecially useful on the black prairie, where the shortage of natural cavities is acute, and in food-producing forest stands too immature for cavity formation. Almost any covered box or keg having an entrance hole and room for a nest will be used by squirrels if placed in a tree on their range. The box recommended here is 2 feet deep, 8 by 8 inches inside cross section, and with an entrance hole 3 inches in diameter. It should have a removable top to facilitate cleaning, which is oc- casionally necessary because squirrels fill boxes with leaves and other materials. Small cracks in the boxes do not seem to interfere wnth use of the box by squirrels, and a perch will be used if present but is not necessary. Boxes constructed from nail kegs or sound old lumber will last Fig. 40.—Two types of artificial den boxes suitable for squirrels. A box having a mini- mum cross section of 8X8 inches, at least 2 feet deep and with an entrance 3 inches in diameter, is recommended. for 2 or 3 years or longer. Such boxes can be built and erected for a small sum each ; if made of cypress or cedar lumber that must be purchased as new, the cost will be higher. However, nests made of the better material will give, with some repair, at least 10 years of service. Two or three boxes per acre are ample, and they should be placed in the larger trees, 20 feet or more above ground. In order to insure the most effective utilization, they should not be placed in den trees, but in- stead in sound trees some distance away from den trees. On large tracts, boxes placed on or near the timber edge are more attractive, at least to fox squirrels, than those 100 yards or more inside the stand. Where ample tree cavities already exist, it is a waste of time and materials to in- stall artificial dens, and for this reason their use in most all-age stands is unnec- essary. Control of Fire and Grazing.—The burning and grazing of woodlands in Illi- September, 1945 Brown & Yeager: Squirrels in Illinois 523 nois is a common practice. About 10 years ago, approximately 75 per cent of all timbered area in the state was grazed (U. S. Department of Commerce 1935), and an unknown, but appreciable, per- centage is burned annually, especially in the south-central and southern counties. Both burning and grazing are injurious to timber growth as well as to the site, as has been pointed out many times. Due to the arboreal nature of squirrels, fire and grazing are not so injurious to them as to ground-frequenting birds and certain other wildlife. In woodlots hav- ing very heavy ground cover, light grazing may be of some benefit both to fox squir- rels (Allen 1941, 1943) and gray squir- rels (Goodrum 1940). However, graz- ing of wooded land gives neither a good pasture nor a good woodlot, and sound land use decrees that stock be kept off forested range. Very heavy grazing un- doubtedly depletes the quality of squirrel habitats w^herever it occurs, since it results in decreased food supply through the destruction of shrubs and brambles. This practice, therefore, may easily result in food shortage, or at least a shortage of certain attractive foods, during the months prior to the ripening of mast. Fire is actually and potentially so des- tructive to Illinois woodlands that its sup- pression in these areas is considered desir- able at all times. There is no evidence pertaining to this state that fire is ever of benefit in squirrel management. Winter Feeding.— It is only during periods of heavy ice or actual food shortage that winter feeding of squirrels in Illinois is recommended. Snow is of little hin- drance to successful foraging, since both fox and gray squirrels dig readily through a foot or more of snow to reach food, fig. 41. On the better oak-hickory range in the state it is rare indeed that feeding is necessary ; and, due to availability of waste corn left by mechanical pickers, it is needed on the extensive black prairie type only during periods of heavy ice. If conditions warrant feeding, it is recommended that ear corn, hickory nuts, w^alnuts or unroasted peanuts be used. Corn, because of its abundance, avail- ability and attractiveness to squirrels, is by far the most practical emergency food. Ears may be impaled on spikes driven up- right through small poles or boards ; nuts may be placed in trays or hoppers in such a manner as to prevent excessive scatter- ing. A corn shock near the woods border makes a simple and effective feeder. Feed- ing operations should be centered on the best squirrel range, to take advantage of maximum cavity and natural food avail- ability. Chapman & Baumgartner ( 1939) recommended one feeding station per 25 Fig. 41.—Squirrels are capable of digging through a foot or more of snow in finding Osage orange fruits or stored nuts or acorns. 524 Illinois Natural History Survey Bulletin Vol. 23, Art. acres of woodland. Hawkins (1937) es- timated that individual squirrels consumed about 2 pounds of shelled corn per week. A practical feeding station is shown in fig- ^2. . . Winter feeding projects are relatively easy to organize among sportsmen and con- servationists, but such activities are also sound open seasons on fox and gray squir- rels in Illinois. The Illinois squirrel season has always begun early and lasted long, and the bag limit has been liberal. Despite heavy hunting and extensive habitat depletion in the state, squirrels, particularly fox squir-^ rels, have maintained appreciable popula- Fig. 42.—A practical winter feeding station—standing corn adjacent to a woodlot and hedgerow, Champaign County. easy to neglect during severe weather. A feeding program, if it is neglected during a critical period, especially after squirrels or other game have been concentrated by feeding during mild weather, may do more harm than good to the animals. Hunting Seasons The regulations under which squirrels are hunted are among the most important factors in their management. One of the ultimate objectives of this study was the determination of dates for biologically m\ tions. This circumstance attests eloquent- 1}' to high quality in much of the Illinois squirrel range. A comparison of the 1944 season in Illinois with seasons in other central states is given in table 26. Of the midwest states, only Missouri and Kentucky, with 153-day and 84-day seasons, respectively, had longer open seasons than the central and northern zones in Illinois. Only Missouri had an earlier season than the southern zone. The daily bag limit in- the midwest states was rather uniform, table 26, and appar- ently satisfactory. Only Michigan had a September, 1945 Brown & Yeager: Squirrels in Illinois 525 season limit on the kill, the total being 25. It is interesting to note that long seasons are, for the most part, in those states where the oak-hickory forest type is most extensive. These forests, in the central states, probably reach their best development in Missouri and Illinois. That this correlation of season with habi- tat should occur is perhaps significant ; it appears to be an instance in which the law of supply and demand exerts a dominating influence on legislation governing the utili- zation of a wildlife resource. Eflfect of Early Seasons.—The basic effects of early-season hunting may be summarized as follows : ( 1 ) Approxi- mately 50 per cent of the kill is of first- litter young; (2) the kill includes a considerable portion of the pregnant and lactating females; and (3) many young squirrels too immature to be self-sustaining die of starvation. From a biological standpoint, there is no real objection to a high percentage of young squirrels in early-season bags. Ma- ture animals appear to be the more certain winter-season breeders. From the stand- point of the hunter, young squirrels rank higher than old, as they are of maximum tenderness and palatability, whereas breeding squirrels, particularly spent males and lactating females, are relatively low in these qualities. The chief objection to early-season hunting is that it results in the destruction of pregnant and lactating females ; the pregnant animals involve unborn young, and many of the lactating females involve Table 26.—Squirrel hunting seasons in midwest states, 1944. 526 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 young too immature to be self-providing. Cross (1942) found 100 per cent preg- nancy during the period September 1—15 in a sample of 39 adult squirrel females in Virginia. The calculated degree of loss in unborn and immature squirrels resulting from an early hunting season in Illinois is given in table 27. The calculations in this table are from data given in tables 2, 3, 15 and 20. The dates of the period included in table 27 (July 16-October 31) were chosen because they are a compromise between the 1944 hunting seasons in the central and southern zones, where most of the squirrel kill was made and where most of the data in tables 15 and 20 were gathered in the years of this study. Table 3 indicates that of each 100 squirrels bagged during the period July 16—October 31 (the kill during the period of Novem- ber 1-15 in the northern zone is negligible, while the kill during the period July 15^31 in the southern zone is appreciable), ap- proximately 70 per cent were fox squirrels and 30 per cent were gray squirrels. In each 100 animals, there was an average of 12.8 mature and therefore potentially breeding fox squirrel females and 7.7 po- tentially breeding gray squirrel females (figures derived from table 15). Preg- nant among these mature females was an average of 3.7 fox squirrels and 2.9 gray squirrels, and lactating among them was an average of 3.7 fox squirrels and 2.4 gray squirrels. The average number of young per lit- ter during the second season, as determined in the Illinois study, was 2.57 in fox squir- rels and 2.43 in gray squirrels, table 20. Calculations based on these data give, for each bag of 100 squirrels, a loss of 9.5 unborn young and 9.5 suckling young of the fox squirrel, and 7.0 unborn young and 5.8 suckling young of the gray squirrel. Only females showing unmistakable evi- dence of lactation were classified as lac- tating; additional losses in young may have resulted through killing of mothers in the last stages of lactation or those still exercising parental care over young. The losses in unborn and suckling young were in addition to squirrels bagged and fatally hit by hunters in the period beginning July 16 and ending October 31, table 23. For each 100 squirrels bagged, 31.8 unborn and suckling animals, table 27, as well as the squirrels fatally wounded and not recovered, must be added to the kill in order to obtain the total theoretical loss. The net loss might be somewhat less due to the fact that squirrels suffer some mor- tality during the post-natal and juvenile periods. This loss, although not known, is probably low, since the young are rela- tively free from predation and usually are well protected against the elements. A calculation of the total loss of unborn and suckling young may be made by ap- plying the findings in table 27 to the total kill, which, as discussed under the heading "Kill," was calculated for 1942 at 1,463,- 305 animals. The ratio of 31.8 young lost for every 100 squirrels bagged applied to this kill figure gives 465,331 as the cal- culated number of young lost in an Illinois season that begins early, July 16, and con- tinues through October. Recommended Seasons.—The one change needed in current Illinois laws to provide a biologically sound squirrel hunt- ing season is a later opening date in each zone. In recommending this change, how- ever, the writers have not forgotten that early seasons are traditional in the state, and that there are thousands of hunters who sincerely believe in summer squirrel hunting. That these hunters argue with some logic is indicated by the fact that, despite early hunting seasons in the past, in many parts of the state there is still good squirrel hunting. However, abun- dance of squirrels in certain areas may be the result of one or more of a number of conditions, some of them local, that favor squirrel survival. In some parts of the state hunting is comparatively rare early in the season and is intensive only through the peak of the mast season, roughly August 15 to September 15. In many places, late in the season, when squirrels are scarcer and the population becomes scattered, interest in squirrel hunting de- creases. In some agricultural communi- ties the fall farm harvest requires the at- tention of a large number of potential hunters. In many counties, the advent of the dove, waterfowl and upland game seasons further reduces the number of squirrel hunters. It is probable that the 76- to 93-day season in Illinois results in only a slightly larger kill than would a 45-day season coming during the main mast season. However, a season be- September, 1945 Brown & Yeager: Squirrels in Illinois 527 Table 27.—Calculated loss in unborn and suckling young per 100 squirrels bagged in Illinois, July 16-October 31, inclusive, 1940-1943. A kill ratio of approximately 70 fox squirrels to 30 gray squirrels was obtained from Illinois kill figures, table 3. Types of Loss bv Species Mature, potentially breeding, females (tabic 15j Fox squirrels, 21 of 115 animals (tables 14 and 15; 18.3% of 70 animaisj Gray squirrels, 16 of 62 animals (25.8% of 30 animals) Pregnant (table 15) Fox squirrels, 6 of 21 mature females (28.6% of 12.8 mature females) .... Gray squirrels, 6 of 16 mature females (37.5% of 7.7 mature females) . . . Lactating (table 15) Fox squirrels, 6 of 21 mature females (28.6% of 12.8 mature females). . Gray squirrels, 5 of 16 mature females (31.3% of 7.7 mature females). . Unborn young* P'ox squirrels (3.7 x 2.57) 9.5 Gray squirrels (2.9 x 2.43) 7.0 Total unborn young Number Per 100 Squirrels (70 Fox Squirrels, 30 Gray Squirrels) 12 8 7,7 3.7 2.9 3.7 2.4 16.5 Suckling young* Fox squirrels (3.7 x 2.57) 9.5 Gray squirrels i2.4 x 2.43) 5.8 Total suckling young. Tolij/ loss . 15.3 ^Average size of second-season litters: fox squirrels, 2.57; gray squirrels, 2.43; table 20. ginning later than the present one would result in the survival of a much greater number of unborn and suckling squirrels that now are lost through destruction of pregnant and lactating females. In the face of the considerations listed above, we feel that it would be unwise to enact a squirrel season beginning ifo late that it would prevent all losses attribut- able to the killing of pregnant and lactating females. Such a season could hardl}' be- gin earlier than October 1, and it would certainly be opposed by a large number of hunters. On the other hand, it is clear that the 1944 season, opening July 15 in the southern zone and August 15 in the central and northern zones, is too early, and that such a season results in the death of many thousands of squirrels that are not bagged. We suggest as a reasonable com- promise the seasons given in table 28, which takes into consideration the prece- dent for early hunting in the state, the minimum requirements for adequate re- production, and the high productive ca- pacity of much of the Illinois squirrel range. It goes without sa>ing that, although the seasons proposed here will result in ap- preciable loss due to starvation of young, this loss will be materially less than at present. In time it may be practical to enact laws establishing seasons that give squirrels greater protection in order still further to reduce juvenile losses. It is not out of place to point out that seasons 528 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 Table 28.—Recommended squirrel hunting seasons in Illinois. Zone September, 1945 Brown & Yeager: Squirrels in Illinois 529 tionnaire. The writers endorse the limit i of five squirrels per hunter per da). SUMMARY 1. This investigation (Illinois Federal Aid Project 14-R) was initiated in fur- therance of biologically sound squirrel hunting seasons and progressive squirrel management in Illinois. 2. Field work covered a 4-year period ; the first 2 years, beginning July 1, 1940, : were given to a full-time study and the i last 2 years to part-time study. During the first year, 10 days per month were spent by the senior author in each of the three zones into which the state is divided for administration of hunting laws; dur- ; ing the second year, intensive local study , was pursued by the same author in Pike I County, in the central zone, and in other j representative areas inhabited by both fox ' and gray squirrels. Part-time field work, by the junior author, was carried on mainly in the central zone. 3. No completely satisfactory census technique was developed. The need for such is obvious. Time-area counts of animals and nest counts probably give a ' rough census. Exhaustive live trapping supplies reliable population numbers, but is too slow and time-consuming for wide- scale use. 4. The western fox squirrel (Sciurus uitjer rufivetiter) inhabits most wooded areas, including small woodlots and hedge- rows, in every Illinois county. The gray squirrel {S. carolinensis leucotis and/or 5. c. carolinensis) occurs in all Illinois counties except some on the black prairie. It is confined to dense forest stands and is most numerous in those with brushy under- , story in the river bluffs and bottoms areas, j The red squirrel {Tamiasciurus hudson- \ icus loquax) was not found in Illinois by I the writers. I 5. Fox squirrel density in the areas I studied varied from 0.02 to 2.23 animals j per acre. Gray squirrel density, on one representative area, w-as 1.49 per acre; the combined density of both species in this area was 2.34 per acre. An average of about one squirrel per acre on good j Illinois habitat appears likely. I 6. Species ratio (based on hunters' ' kill in the 1940 and 1941 seasons) was 69.7 fox squirrels and 30.3 gray squirrels. The ratio varied by zones; being 86.1 fox squirrels to 13.9 gray squirrels in the northern zone, 87.4 to 12.6 in the central zone and 49.5 to 50.5 in the southern zone. Species ratios based on other source data and for other years differ somewhat, and indicate that gray squirrels may constitute as much as 35 per cent of the squirrel population of this state. 7. Sex ratios (based mainly on hunt- ers' kill in 1940 and 1941 and to a small extent on litters and live- and steel-trapped animals) showed a preponderance of males in both species. The ratio was 143 males to 100 females in fox squirrels and 144 males to 100 females in gray squirrels. The actual sex ratios are believed to be more nearly equal than these figures indi- cate. 8. The best criteria of maturit\ in males (November—July ) are Cow'per's glands of one-half inch or more in diam- eter and enlarged testes with scrotum de- void of hair (or nearly so) on entire ven- tral surface ; for females, large, dark and protruding nipples. Immature males have undeveloped Cowper's glands even during the mating season and only the posterior end of the scrotum devoid of hair ; immature females have mammae with small nipples nearly hidden by hair. 9. Age class figures for Illinois fox squirrels, as indicated by several hundred animals shot and trapped by the writers, were as follows: 57.8 per cent adults, 26.7 per cent spring juveniles and 15.5 per cent summer juveniles; for gray squirrels the figures were, respectively, 65.4, 22.4 and 12.2 per cent. The comparatively low kill of summer juveniles is undoubtedly an important factor in maintaining s(]uirrel populations. 10. Little or no competition between fox and gray squirrels was observed. 11. Both species were most active early in the morning, the hour of greatest ac- tivity being from 6 : 00 to 7 : 00. The greatest activity hour for the afternoon was, in fox squirrels, between 4 : 00 and 5 : 00 ; in gray squirrels, between 5 : 00 and 6:00. The fox squirrel showed the greater tendency to be active during inid- day hours; the gray was active later in the evening. Individuals of both species were seen to be active during showers, or soon after, and in deep snow ; in both spe- cies, high winds, heavy rains, snow- 530 Illinois Natural History Survey Bulletin Vol 23, Art. 5 storms, very high temperatures and also very low temperatures appeared to reduce activity. 12. The two types of movements noted in squirrel populations were daily activity, mainly associated with feeding, and sea- sonal dispersal, perhaps associated with the annual readjustment of populations, in the late summer and fall. The former usually involved only a few acres ; the latter, probably up to several miles. Mass migration was not observed in either species although it has been reported often in the gray squirrel. 13. Neither weight nor length of squirrels proved to be a reliable indicator of age at all seasons of the year. Adult fox squirrels taken in a 2-year period av- eraged about 1.70 pounds; adult grays, 1.18 pounds. Spring-born juvenile fox squirrels weighed 1.61 pounds by No- vember; spring-born juvenile gray squir- rels, 1.27 pounds by October. Length was found to be probably an even less reliable age indicator than weight. 14. Stub tail was the only deformity observed; 13.5 per cent of all fox squirrels and 12.3 per cent of all gray squirrels ex- amined were affected. This deformity, probably due to fighting and mating chases, in no way impeded travel or other activity. 15. Only six of the squirrels collected showed wounds of serious nature. Most badly wounded animals that escape hunters are believed to die in dens, nests or other retreats. 16. Fox and gray squirrels molt once annually, both species undergoing a body and then a tail phase. Males and spring juveniles molt before females, usually be- fore midsummer. Females that produce second-season litters molt last, beginning after lactation is under way. Few color types were found in Illinois squirrels. 17. Neither parasites nor diseases ap- peared to be of importance in Illinois squirrel populations. Mange, the most prevalent disorder, was observed in only two localities (cities excepted), neither serious. Predators likewise appeared to cause little loss; adult squirrels are too active and alert, and the young are too well protected to be captured easily. 18. Breeding studies were based main- ly on 722 fox squirrels and 353 gray squir- rels handled in the laboratory. Specimens of both species were available each month from July, 1940, to October, 1942. Other biological and all ecological studies were based on these animals, an additional 2,594 fox squirrels and 1,121 gray squir- rels taken mainly by hunters, and more than 2 years of field observations. 19. Both fox and gray squirrels have two breeding seasons per year, the first in winter and spring and the second in spring and summer. Second-season litters appear to be confined largely to vigorous females over 18 months old. Both spring-born and summer-born animals attain sexual maturity at the age of about 10 to 12 months, and the females produce their first young when approximately a year old. 20. In Illinois the breeding season of fox squirrels precedes that of gray squir- rels by about 10 days or 2 weeks. Be- tween the northern and southern limits of Illinois there is a difference of about 3 weeks in the average breeding dates for both species. In the central zone, the peak of winter breeding determined for fox squirrels was in late December ; in gray squirrels in early January; summer breeding peaks, for fox squirrels, the first 2 or 3 weeks in June; for gray squir- rels, the last half of June or a little later. Corresponding peaks may be expected ap- proximately a week earlier and later, re- spectively, in the southern and northern zones. 21. Mating chases, often involving, several squirrels, are characteristic of both I species. In males, enlarged testes and Cowper's glands are obvious indications' of breeding condition, and the scrotal sacn becomes smooth and stained as the breed-1 ing season advances. In females, oestrus i is indicated by the swollen and discolored vulva. 22. In both species gestation appears to require about 44 or 45 days. In the fox squirrel, pregnancy peaks occurred in early February and late July; lactation peaks in March and August. In the gray squirrel, corresponding peaks were about ^ 10 days to 2 weeks later. Lactation in' the gray squirrel extended into October. 23. Squirrels are born both in tree cavities and in leaf nests, more commonly in the former. The average number of young in the litters counted was, in fox squirrels, 2.49 in spring and 2.57 in , summer; in gray squirrels, 2.74 in spring September, 1945 Brown & Yeager: Squirrels in Illinois 531 and 2.43 in summer. The eyes of juve- nile squirrels open at about 4 weeks; weaning occurs at about 8 to 10 weeks, at which time the hair is well developed. Young squirrels become fully self-sustain- ing when between 3 and 4 months old. 24. Illinois squirrel habitats are of two types, agricultural and woodland. The former consist mainly of farm wood- lots, hedgerows and wooded stream valleys ; the latter, the more extensive wooded areas, both upland and bottom- land in character. The upland and bottomland types combined provide rough- ly 6,750,000 acres of squirrel range in the state ; agricultural types provide a much smaller acreage of habitable range. Minor habitat types consist of reforested stripmines, estates, parks, college campuses, and many towns and cities. 25. During this investigation, a total of 76 kinds of food plants for Illinois squirrels were recorded; these included 56 trees and shrubs, 2 vines, 4 brambles, 6 wild herbs, 7 cultivated crops and various fungi. Six groups provided most of the staple foods—-hickories (including pecan), oaks, walnuts, elms, mulberry and field corn. In Illinois almost any fruit may be important seasonally or locally. Mixed stands produce the greatest variety and abundance of food. Cultivated crops, mainly corn, are of far greater importance to fox squirrels than to gray squirrels. No study of the animal food of squirrels was made. Squirrel food shortage ap- peared to be rare on Illinois range. 26. Illinois squirrels follow a some- what distinct order of succession in the utilization of foods. In late winter or spring they feed on the buds and then the flowers and seeds of elms, maples and other hardwoods. Later they make use of mul- berries and bramble fruits. The mast season, from July or August through Oc- tober, is the period of greatest food abun- dance. 27. Squirrels show definite preferences when several foods are abundant at one time. Hickory nuts seem to rank first with both fox and gray squirrels. 28. Storing or caching, which seems to be instinctive in squirrels, is apparently an extension of the morning and afternoon feeding periods during the mast season. The stored foods observed in the present study were mainly nuts and acorns. 29. The gnawing of bones, observed in both squirrel species, may be for the purpose of obtaining minerals. 30. Fox squirrels apparently are able to inhabit range lacking open water, pro- vided succulent foods such as green corn, blackberries or Osage orange fruits are available. Gray squirrels were never found on areas entirely devoid of open water. 31. Both fox and gray squirrels use cavity and leaf nests, and in both species cavities are important as young-rearing sites. Either type of nest appears to meet the essential requirements of either species, but both types of nests are found in the habitats of highest quality. Squirrels utilize practically any kind of tree for nest location, but, because of abun- dance and statewide distribution, the oaks are by far the most important group. The oaks, maples, American elm, white ash, beech, sweet gum, and, in extreme southern counties, cypress and tupelo gum are the chief sources of nest cavities for Illinois squirrels. 32. Squirrel hunters are mainly farm- ers, laborers and small-town businessmen. Slightly more than one squirrel killed per hour was reported by a group of 236 Illi- nois hunters in 1940 and 1941. A bag figure believed to be more nearly represen- tative for Illinois is between 0.5 and 1.0 squirrel per hour. Crippling loss, calcu- lated from hunters' reports, was about 15 per cent of all squirrels known to have been hit; this figure does not take into account the loss in squirrels not known to have been hit. The 12-gauge shotgun was the most popular arm of Illinois hunters, followed by the .22-caliber riHc and the 16-gauge shotgun. 33. The calculated squirrel kill in Illinois in 1942 was 1,463,305 animals, of which 64.7 per cent were fox squirrels and 35.3 per cent were gray squirrels. The northern zone produced 11.4 per cent, the central zone 29.1 per cent and the southern zone 50.5 per cent of this kill. A total of about 1,240,000 pounds of high quality meat was produced, practically all of which was used for human food. 34. In general, good forest practices, especially the maintenance of mixed, all- age stands and protection from fire and grazing, lend themselves to good squirrel management. Selective cutting, except 532 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 when a large percentage of the food trees are removed, may improve the range as squirrel habitat by breaking up solid stands and promoting shrub, vine and bramble growth in the openings. Only a few hickories, elms or mulberries, in ad- dition to oaks, beech or maples, are needed in a stand to provide all necessary squirrel food. Development of fencerows and hedgerows greatly improves fox squirrel range on the prairie. Den boxes are need- ed only where cavity shortage actually exists. Winter feeding is unnecessary except during periods of crusted snow, heavy ice or actual food shortage. 35. The Illinois squirrel hunting season is traditionally long and is early in starting; in the past it has usually opened in midsummer and continued 75 days or more. Such a season may result in a cal- culated loss of 31.8 unborn and suckling squirrels for each 100 squirrels bagged, or a total yearly loss of approximately 465,000 unborn and suckling squirrels (hunters' kill, 1942, used as a basis). 36. The squirrel hunting season re- commended for Illinois is September 15 to November 15 in the northern and central zones, and September 1 to October 31 in the southern zone. This season will not prevent all loss in unborn and nursing squirrels, but will materially reduce the losses now occurring. Recent severe de- pletion of the habitat, due to heavy cutting to meet war needs, is an added reason for a hunting season based upon serious con- sideration of the life history of the animals. LITERATURE CITED Allen, Durward L. 1910. A point on fox squirrel management: Shooting into nests is wasteful hunting. Mich Cons. 9(12) : 11. 1 fig. 1941. Rose Lake Wildlife Experiment Station; Second aiuuial report. Mich. Dept. Cons. Game Div. 365 pp. (Mimeographed.) 1942. Populations and habits of the fox squirrel in Allegan County, Michigan. Am. Midland Nat. 27(2) : 338-79. 19 figs. 1943. Michigan fox squirrel management. Mich. Dept. Cons. Game Div. Pub. 100. 404 pp., 152 figf , index. Anderson, R. M. 1932. Methods of collecting and preserving vertebrate animals. Can. Natl. Mus. Bui. 69. 141 pp., 46 figs. Baker, Rollin H. 1944. An ecological study of tree s(iuirrels in eastern Texas. Jour. Mammal. 25 ( 1 ) : 8—24. 5 figs. Baumgartner, Luther L. 1938. Population studies of the fox squirrel in Ohio. N. Am. Wildlife Conf. Trans. 3, 1937:685-9. 1939rt. Foods of the fox squirrel in Ohio. N. Am. Wildlife Conf. Trans. 4, 1938:579-84. 1939//. Fox squirrel dens. Jour. Mammal. 20(4) : 456—65. 3 pis. 1940. Trapping, handling, and marking fox squirrels. Jour. Wildlife Mgt. 4(4):444— SO. 1 pi., 16 figs. 1943fl. Fox squirrels in Ohio. Jour. Wildlife Mgt. 7(2) : 193-202. 1 pi. 1943/a Pelage studies of fox squirrel (Sciurus niger rufiventer) . Am. Midland Nat. 29(3): 588-90. Boulware, Jean T. 1941. Eucalyptus tree utilized by fox squirrel in California. Am. Midland Nat. 26(3): 696-7. 1 fig. Brooks, Fred E. 1922. Note on a feeding habit of the gray squirrel. Jour. Mammal. 4(4) : 257—8. Brown, Louis G., and Frank C. Bellrose, Jr. 1943. l^se of nesting boxes for wood ducks by other wildlife. Jour. Wildlife Mgt. 7(3) : 298-306. 1 pi. Cahalane, Victor H. 1942. Caching and recovery of food by the western fox squirrel. Jour. Wildlife Mgt. 6(4) : 338-52. Carlson, A. J. 1940. Eating of bone by the pregnant and lactating gray squirrel. Sci. n. s. 9! (2372) : 573. Case, H. C. M., and K. H. Myers 1934. Types of farming in Illinois. III. Ag. Exp. Sta. Bui. 403. 226 pp., 40 figs. Chandler, Asa C. 1942. Helminths of tree squirrels in southeast Texas. Jour. Parasitol. 28(2) : 135-40. 3 figs. Chapman, Floyd B. 1936. Fox squirrels and gray squirrels. Ohio Div. Cons. Bui. 127. 4 pp. (Mimeographed.) 1937. Controlled squirrel and rabbit hunting on state hunting preserves, 1936. Ohio Wild- life Res. Sta. Release 37. 11pp. (Mimeographed.) 1938rt. Controlled squirrel hunting on Ohio hunting preserves, 1937. Ohio Wildlife. Res. Sta. Release 68. 8 pp. (Mimeographed.) \9ZU. Summary of the Ohio gray squirrel investigation. N. Am. Wildlife Conf. Trans. 3, 1937:677-84. 1939. A summary of the gray squirrel investigation in southeastern Ohio. U. S. Dept. Ag. Wildlife Res. and Mgt. Leaf. BS-134. 9 pp. (Mimeographed.) [533] 534 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 Chapman, Floyd B., and Luther L. Baumgartner [1939.] Winter feeding of squirrels. Ohio Div. Cons. Bui. 150. 7 pp., 1 pi. Cottam, Clarence 1941. How fast can a fox squirrel run? Jour. Mammal. 22(3) : 323. Coventry, A. F. 1940. The eating of bone by squirrels. Sci. n. s. 92(2380) : 128. Cross, R. H., Jr. [1942.] Breeding habits and management of the gray squirrel in Virginia. Va. Comm. Game and Inland Fish. 5 pp. (Mimeographed.) Dambach, Charles A. 1942. Gray squirrel feeding on Crataegus. Jour. Mammal. 23(3) : 337. Davis, Wni. T. 1907. Insects as the food of squirrels. Can. Ent. 39(1) : 16. 1924. Oak apple galls destroyed by gray squirrels. Brooklyn Ent. Soc. Bui. 19(3) : 91—3. 1 fig. Deuber, Carl G. 1934. Defoliation activities of gray squirrels in American elm trees. Sci. Monthly 38: 60—3. lUus. Dice, Lee R. 1931. Methods of indicating abundance of mammals. Jour. Mammal. 12(4) : 376— 81. 1941. Methods for estimating populations of animals. Jour. Wildlife Mgt. 5(4) : 398—407. Dozier, Herbert L., and Harrold E. Hall 1944. Observations on the Bryant fox squirrel. Md. Cons. 21(1) :2— 6. lllus. Edminster, Frank C. 1937. An analysis of the value of refuges for cyclic game species. Jour. Wildlife Mgt. 1(1-2): 37-41. Goodrum, Phil D, 1938. Squirrel management in east Texas. N. Am. Wildlife Conf. Trans. 3, 1937:670—6. 1940. A population study of the gray squirrel in eastern Texas. Tex. Ag. Exp. Sta. Bui. 591. 34 pp., 5 figs. Goodwin, George G. 1934. The gray squirrel migration. Nat. Mag. 23(5) : 221—2, 255—6. 2 photos. Graham, Edward, and Jacob Uhrich 1943. Animal parasites of the fox squirrel, Sciuriis n'lger rufiventer, in southeastern Kansas. Jour. Parasitol. 29(2) : 159-60. Hahn, W. L. 1909. The mammals of Indiana. Ind. Dept. Geol. and Nat. Res. Ann. Rep. 33: 417—654. Hamilton, W. J., Jr. 1943. Caterpillars as food of the gray squirrel. Jour. Mammal. 24(1) : 104. Harkema, Reinard 1936. The parasites of some North Carolina rodents. Ecol. Mono. 6(2) : 153—232. Hawkins, Arthur S. 1937. Winter feeding at Faville Grove, 1935-36. Am. Midland Nat. 18(3) : 417-25. Hawkins, Arthur S., and Frank C. Bellrose, Jr. 1941. Wood duck habitat management in Illinois. N. Am. Wildlife Conf. Trans. 5, 1940:392-95. September, 1945 Brown & Yeager: Squirrels in Illinois 535 Haymond, Rufus 1869. Mammals found in Franklin County, Indiana. Ind. Ag. and Geol. Rep. 1869: 203—8. Hesselschwerdt, Robert E. 1942. Use of den boxes in wildlife restoration in intensively farmed areas. Jour. Wildlife Mgt. 6(1) : 31-7. 4 pis. Hibbard, Claude W. 1935. Breeding seasons of gray squirrel and flying squirrel. Jour. Mammal. 16(4) : 325-6. Hicks, Ellis A. 1942. Some major factors affecting the use of two inventory methods applicable to the western fox squirrel, Sciurus niger rufiventer (Geoffroy). Iowa State Col. Jour. Sci. 16(2) : 299-305. Hungerford, K. E., and N. G. Wilder ^ 1941. Observations on the homing behavior of the gray squirrel {Sciurus carolinensis) . Jour. Wildlife Mgt. 5(4) : 558-60. Jackson, H. H. T. 1910. The distribution of certain Wisconsin mammals. Wis. Nat. Hist. Soc. Kul. 8(2) : 86—90. 1921. A recent migration of the gray squirrel in Wisconsin. Jour. Mammal. 2(2) : 113—4. Katz, Julius S. 1939. An annotated bibliography of references concerning parasites of squirrels (family Sciuridae). Ohio Wildlife Res. Sta. Release 131. 21pp. (Mimeographed.) Kennicott, John 1857. The quadrupeds of Illinois, injurious and beneficial to the farmer. U. S. Pat. Off. Rep. Ag. for 1856, pp. 54-67. Leopold, Aldo 1933. Game management. Charles Scribner's Sons, New York, xxil 481 pp., 35 figs. Lyon, M. W., Jr. 1936. Mammals of Indiana. Am. Midland Nat. 17(1): 1-384. 112 figs. Middleton, A. D. 1930. The ecology of the American gray squirrel (Sciurus carolinensis Gmelin) in the British Isles. London Zool. Soc. Proc, pt. 3, 1930: 809-43. 4 figs., 6 pis. Mossman, H. W., John W. Lawlah and J. A. Bradley 1932. The male reproductive tract of the Sciuridae. Am. Jour. Aiiat. 51 ( 1 ) : 89— 155. 7 pis., 16 figs. Necker, Walter L., and Donald M. Hatfield 1941. Mammals of Illinois. Chicago Acad. Sci. Bui. 6(3) : 17-60. 15 figs. Nichols, John T. 1927. Notes on the food of the gray squirrel. Jour. Mammal. 8(1) : 55-7. Osgood, Frederick L., Jr. 1938. The mammals of Vermont. Jour. Mammal. 19(4) : 435-41. Pearce, John 1938. Identifying tooth marks of some northeastern animals on forest vegetation. N. Am Wildlife Conf. Trans. 3, 1937:690-4. Seton, Ernest T. 1928. Lives of game animals. Literary Guild of Am., Inc., New York. 4: 9-S8 ; 82-106. Illus. Stoddard, H. L. 1920. Nests of the western fox squirrel. Jour. Mammal. 1 (3) : 122— 3. 1 pi. 536 Illinois Natural History Survey Bulletin Vol. 23, Art. 5 U. S. Department of Commerce 1936. United States Census of Agriculture: 1935. Vol.1, xxxix+950 pp. Terres, J. Kenneth 1939. Gray squirrel utilization of elm. Jour. Wildlife Mgt. 3(4): 358—9. Terrill, H. V. 1941. A preliminary study of the western fox squirrel, Sciurus niger rufiventer (Geoffroy), in Missouri. Graduate thesis, University of Missouri. 164 pp. Whitaker, H. L. 1939. Fox squirrel utilization of Osage orange in Kansas. Jour. Wildlife Mgt. 3(2) : 117. 1 pi. Woods, Gordon T. 1941. Mid-summer food of gray squirrels. Jour. Mammal. 22(3) : 321. Yeager, Lee E. 1936. Fox squirrel seriously damages elm tree. Jour. Mammal. 17(4): 417— 8. 1942. Coal-stripped land as a mammal habitat, with special reference to fur animals. Am. Midland Nat. 27(3): 613-35. 8 figs. Yeatter, Ralph E., and David H. Thompson 1943. Cottontails, tularemia and weather. 111. Cons. 8(4): 6—7, 36. Illus. ^W' Recent Publications A.—ILLINOIS NATURAL HISTORY SURVEY BULLETIN. Volume 21, Article 6.—Preliminary Investigation of Oak Diseases in Illinois. By J. Cedric Carter. June, 1941. 36 pp., frontis. + 51 figs., bibliog. (Bound with Article 7.) Volume 2l! Article 7.—A Needle Blight of Austrian Pine. By Robert L. Hulbary. June, 1941. 6 pp., frontis. + 3 figs., bibliog. (Bound with Article 6.) Volume 21, Article 8.—Duck Food Plants of the Illinois River Valley. By Frank C. Bellrose, Jr. August, 1941. 44 pp., frontis. + 35 figs., bibliog., appendix. Volume 22, Article 1.—The Plant Bugs, or Miridae, of Illinois. By Harry H. Knight. September, 1941. 234 pp., frontis. + 181 figs., bibliog., index. $1.25. Volume 22, Article 2.—Studies of North American Plecoptera, with special reference to the fauna of Illinois. By T. H. Frison. September, 1942. 122 pp., frontis. + 126 figs., bibliog., index. $1.00. Volume 22, Article 3.—Management of Small Artificial Lakes: a summary of fisheries investigations, 1938-1942. By George W. Bennett. February, 1943. 20 pp., frontis. + 7 figs., bibliog. Volume 22, Article 4.—The Prairie Chicken in Illinois. By Ralph E. Yeatter. May, 1943. 40 pp., frontis. -f 18 figs., bibliog. (Bound with Article.5.) Volume 22, Article 5.—Preferential Rating of Duck Food Plants. By Frank C. Bell- rose, Jr., and Harry G. Anderson. May, 1943. 16 pp., frontis. -|- 16 figs., bibliog. (Bound with Article 4.) Volume 22, Article 6.—Survey of the Illinois Fur Resource. By Louis G. Brown and Lee E. Yeager. September, 1943. 70 pp., frontis. + 33 figs., bibliog. (Bound with Article 7.) Volume 22, Article 7.—Illinois Furbearer Distribution and Income. By Carl 0. Mohr. September, 1943. 33 pp., frontis. + 24 figs., bibliog. (Bound with Article 6.) Volume 23, Article 1.—^The Caddis Flies, or Trichoptera, of Illinois. By Herbert H. Ross. August, 1944. 326 pp., frontis. -f- 961 figs., bibliog., index. $1.50. Volume 23, Article 2.—Duck Populations and Kill. By Frank C. Bellrose, Jr. Novem- ber, 1944. 46 pp., frontis. + 27 figs., bibliog. Volume 23, Article 3.—Overfishing in a Small Artificial Lake; Onized Lake near Alton, Illinois. By George W. Bennett. May, 1945. 34 pp., frontis. + 15 figs., bibliog. Volume 23, Article 4.—Wetwood of Elms. By J. Cedric Carter. August, 1945. 42 pp., frontis. + 30 figs., bibliog. B.—ILLINOIS NATURAL HISTORY SURVEY CIRCULAR. (Second printing. P. Flint. (Third By G. H. Boewe. September, 1939. March, 1941. 23 pp., frontis. McCauley and W. P. Flint. August, 32.—Pleasure .With Plants. By L. R. Tehon. November, 1942. with revisions.) 32 pp., frontis. + 9 figs. 33.—Controlling Peach Insects in Illinois. By S. C. Chandler and W. August, 1939. 40 pp., frontis. + 32 figs. 34.—Rout the Weeds! Why, When and How. By L. R. Tehon. August, 1943. printing.) 47 pp., color frontis. + 13 figs. 35.—^Diseases of Small Grain Crops in Illinois. 130 pp., frontis. + 47 figs. 36.—Planting and Care of Shade Trees. By J. E. Davis. -1- 16 figs. 37.—Outwitting Termites in Illinois. By W. E. 1942. (Second printing.) 23 pp., frontis. -f- 19»figs. 38.—Windbreaks for Illinois Farmsteads. By J. E. Davis. February, 1942. (Second printing.) 24 pp., frontis. -f 19 figs. 39.—How to Collect and Preserve Insects. By H. H. Ross. May, 1944. (Second printing, with additions.) 55 pp., frontis. + 63 figs. 40.—Control of Roundheaded Apple Tree Borer. By S. C. Chandler and W. P. Flint. April, 1942. 8 pp., 6 figs. C—ILLINOIS NATURAL HISTORY SURVEY MANUAL. l._Fieldbook of Illinois Wild Flowers. By the staff. March, 1936. 406 pp., color frontis. + 349 figs., index. $1.50. 2.—Fieldbook of Illinois Land Snails. By Frank Collins Baker. August, 1939. 166 pp., color frontis. + 170 figs., 8 pis. $1.00. 3.—Fieldbook of Native Illinois Shrubs. By Leo R. Tehon. December, 1942. 307 pp., 4 color pis. + 72 figs., glossary, index. $1.25. List of available publications ^ about 400 titles, mailed mt- request. Address orders and correspondence to the Chief ILLINOIS NATURAL HISTORY SURVEY Natural Resources Building, Urbana, Illinois Payment in the form of U. S. Post Office money order made out to State Treasurer of Illinois, Springfield, Illinois, must accompany requests for those publications on which a price is set.