474 



Illinois Natural History Survey Bulletin Vol. 23, Art. 5 



Table 11. — Squirrels counted or collected for study in Illinois, 1940—1943. 



laboratory study were taken during every 

 month of the year, table 12. 



Breeding Seasons 



Numerous workers have reported that 

 both fox and gray squirrels are dioestrus, 

 that is, have two breeding seasons an- 

 nually. Allen (1942, 1943), whose 

 studies of the fox squirrel exceed in both 



scope and duration those of any other 

 investigator, found that old females of 

 this species (2 years or more) usually pro- 

 duce two litters per year, but that younger 

 females ordinarily produce only one. 

 Females from spring litters usually breed 

 the following December or January, when 

 about 1 1 months old, giving birth to their 

 first young in late February or March. 

 These young females usually do not breed 



Table 12. — Month of collection, species and sex of squirrels studied in laboratory in Illinois, 

 July, 1940, to October, 1942.* 



Month 



January. . . 

 February. . 

 March . . . . 



April 



May 



June 



July 



August. . . , 

 September 

 October . . 

 November 

 December . 



Total. 



Fox Squirrel 



Male 



53 

 31 

 28 

 18 

 37 

 26 

 26 

 80 

 40 

 31 

 19 

 29 



418 



Female 



38 

 22 

 19 

 12 

 26 

 20 

 23 

 56 

 30 

 22 

 16 

 20 



304 



Gray Squirrel 



Male 



14 

 15 

 11 

 15 

 26 

 13 

 17 

 25 

 17 

 17 

 15 

 15 



200 



Female 



9 

 11 



8 

 11 

 18 

 11 

 15 

 17 

 15 

 13 

 12 

 13 



153 



*Includes 305 fox squirrels and 122 gray squirrels not used in breeding studies, tables 14 and IS. 



