458 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 5 



Sex Ratios 



The sex of 4,651 squirrels, 3,197 fox 

 squirrels and 1,454 gray squirrels, as de- 

 termined during the investigation is 

 shown in table 4. These data were de- 

 rived largel_v from hunters' questionnaires, 

 and were therefore subject to whatever 

 differentials there may have been in bag- 

 ging the sexes. 



It appears that Illinois squirrel popula- 

 tions either have a preponderance of males, 

 or that males are more easily bagged by 

 hunters, who invariably shoot at squirrels 

 in the order of their appearance until the 

 limit is reached or the hunt is over. Fox 

 squirrel males and females were taken in 

 steel traps in approximately the ratios in 

 which they were shot ; gray squirrel males 

 and females were steel trapped in more 

 nearly equal numbers, but with males pre- 

 dominating, table 4. Live trapping, for 

 which the samples are too small for re- 

 liability, yielded in both fox and gray 

 squirrels more females than males, but in 



gray squirrels the numbers were nearly 

 equal for the sexes. Litter counts, on the 

 basis of a very few samples, showed slight- 

 ly more males than females in both species. 

 A summary of figures listed in table 4 

 showed a preponderance of males in both 

 species, giving a male to female ratio of 

 roughly 60 to 40. 



The sex ratio of 17 litters of fox squir- 

 rels, totaling 43 young, recorded during 

 the spring of 1941 was 105 males to 100 

 females, table 4. Of 179 first-season or 

 spring juvenile fox squirrels taken by the 

 writers and by hunters from May through 

 November 15, 62 per cent were males and 

 38 per cent were females; of 109 second- 

 season or summer juveniles taken during 

 September and October, 57 per cent were 

 males and 43 per cent were females. The 

 sex ratio of all juvenile fox squirrels for 

 which records were obtained, including lit- 

 ters, 195 males and 136 females, was 144 

 to 100. 



In gray squirrels, the sex ratio of 3 

 litters, totaling 11 young, was 120 males 



Table 4. — Sex ratio in Illinois squirrels as determined from sample litter counts and from 

 animals shot, steel-trapped and live-trapped, 1940-1943. 



Litters (all zones represented) 



Shot (throughout Illinois; including writ- 

 ers' kill) 



Steel traps (all zones represented) 



Live traps (Pike County) 



Total 



105:100 



146:100 



149:100 



78:100 



143:100 



Gray Squirrel 



Litters (all zones represented) 



Shot (throughout Illinois; including writ 



ers'kill) "^ 



Steel traps (all zones represented) 



Live traps (Pike County) 



Total 



120:100 



154:100 



109:100 



97:100 



144:100 



