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 



