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. 



♦Litter counts by R. E. Hesselschwerdt, leader of Illlnoit- Federal Aid Project 4-R. In March, 1945, the In- 

 spection of den boxes in Urbana Township by Dr. Ralph E. Yeatter revealed four litters totalinB 14 young, an avcr.i).'e 

 lit !.>() per litter. 



t Litter counts by Dr. William H. Elder, Assistant Game Technician, Illinois Natural History Survey. 



