September, 1945 



Brown & Yeager: Squirrels in Illinois 



529 



tionnaire. The writers endorse the limit 

 i of five squirrels per hunter per da). 



SUMMARY 



1. This investigation (Illinois Federal 

 Aid Project 14-R) was initiated in fur- 

 therance of biologically sound squirrel 

 hunting seasons and progressive squirrel 

 management in Illinois. 



2. Field work covered a 4-year period ; 

 the first 2 years, beginning July 1, 1940, 



: were given to a full-time study and the 



i last 2 years to part-time study. During 



the first year, 10 days per month were 



spent by the senior author in each of the 



three zones into which the state is divided 



for administration of hunting laws; dur- 



; ing the second year, intensive local study 



, was pursued by the same author in Pike 



I County, in the central zone, and in other 



j representative areas inhabited by both fox 



' and gray squirrels. Part-time field work, 



by the junior author, was carried on 



mainly in the central zone. 



3. No completely satisfactory census 

 technique was developed. The need for 

 such is obvious. Time-area counts of 

 animals and nest counts probably give a 



' rough census. Exhaustive live trapping 

 supplies reliable population numbers, but 

 is too slow and time-consuming for wide- 

 scale use. 



4. The western fox squirrel (Sciurus 

 uitjer rufivetiter) inhabits most wooded 

 areas, including small woodlots and hedge- 

 rows, in every Illinois county. The gray 

 squirrel {S. carolinensis leucotis and/or 

 5. c. carolinensis) occurs in all Illinois 

 counties except some on the black prairie. 

 It is confined to dense forest stands and is 

 most numerous in those with brushy under- 



, story in the river bluffs and bottoms areas, 

 j The red squirrel {Tamiasciurus hudson- 

 \ icus loquax) was not found in Illinois by 

 I the writers. 



I 5. Fox squirrel density in the areas 



I studied varied from 0.02 to 2.23 animals 



j per acre. Gray squirrel density, on one 



representative area, w-as 1.49 per acre; 



the combined density of both species in 



this area was 2.34 per acre. An average 



of about one squirrel per acre on good 



j Illinois habitat appears likely. 



I 6. Species ratio (based on hunters' 



' kill in the 1940 and 1941 seasons) was 



69.7 fox squirrels and 30.3 gray squirrels. 



The ratio varied by zones; being 86.1 fox 

 squirrels to 13.9 gray squirrels in the 

 northern zone, 87.4 to 12.6 in the central 

 zone and 49.5 to 50.5 in the southern zone. 

 Species ratios based on other source data 

 and for other years differ somewhat, and 

 indicate that gray squirrels may constitute 

 as much as 35 per cent of the squirrel 

 population of this state. 



7. Sex ratios (based mainly on hunt- 

 ers' kill in 1940 and 1941 and to a small 

 extent on litters and live- and steel-trapped 

 animals) showed a preponderance of males 

 in both species. The ratio was 143 males 

 to 100 females in fox squirrels and 144 

 males to 100 females in gray squirrels. 

 The actual sex ratios are believed to be 

 more nearly equal than these figures indi- 

 cate. 



8. The best criteria of maturit\ in 

 males (November— July ) are Cow'per's 

 glands of one-half inch or more in diam- 

 eter and enlarged testes with scrotum de- 

 void of hair (or nearly so) on entire ven- 

 tral surface ; for females, large, dark and 

 protruding nipples. Immature males 

 have undeveloped Cowper's glands even 

 during the mating season and only the 

 posterior end of the scrotum devoid of 

 hair ; immature females have mammae 

 with small nipples nearly hidden by hair. 



9. Age class figures for Illinois fox 

 squirrels, as indicated by several hundred 

 animals shot and trapped by the writers, 

 were as follows: 57.8 per cent adults, 26.7 

 per cent spring juveniles and 15.5 per cent 

 summer juveniles; for gray squirrels the 

 figures were, respectively, 65.4, 22.4 and 

 12.2 per cent. The comparatively low 

 kill of summer juveniles is undoubtedly an 

 important factor in maintaining s(]uirrel 

 populations. 



10. Little or no competition between 

 fox and gray squirrels was observed. 



11. Both species were most active early 

 in the morning, the hour of greatest ac- 

 tivity being from 6 : 00 to 7 : 00. The 

 greatest activity hour for the afternoon 

 was, in fox squirrels, between 4 : 00 and 

 5 : 00 ; in gray squirrels, between 5 : 00 and 

 6:00. The fox squirrel showed the 

 greater tendency to be active during inid- 

 day hours; the gray was active later in 

 the evening. Individuals of both species 

 were seen to be active during showers, or 

 soon after, and in deep snow ; in both spe- 

 cies, high winds, heavy rains, snow- 



