September, 1945 



Brown & Yeager: Squirrels in Illinois 



477 



8 



7 



6 



E 



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 = 26 



22 



18 



TESTES LENGTH 



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i 24 



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JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 

 Fig. 9. — Breeding seasons in male squirrels in Illinois, 1940—1942. 



particularly to the central zone ; in the 

 northern and southern zones, the time of 

 corresponding peaks may, in general, be 

 expected about 6 or 7 days later and 

 earlier, respectively. 



Duration of the oestrual period, on the 

 basis of evidence at hand, is approximately 

 10 days. Peak dates for pregnancy and 

 lactation are less easily established, since 

 gestation requires about 45 days and 

 nursing continues for 8 to 10 weeks. Av- 



erages of all data, tables 15 and 16, indicate 

 that pregnancy peaks in fox squirrels were 

 reached about February 1-15 and July 

 16—31 ; in gray squirrels, February 10-25 

 and August 5-20. Lactation peaks in 

 fox squirrels occurred during the months 

 of March and August; in gray squirrels 

 April and September. 



Considerable overlap was found in the 

 two breeding and young-rearing seasons. 

 Ending the first season was a lactation 



