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 



