Vo1. 5, No. 3 
Page 4 
of the fall population died due to natural causes. These figures indicate that 
perhaps the mortality due to hunting caused a reduction in the natural mortality 
from 47.5 per cent of the fall population during 1960-61 to 37 per cent during the 
1961-62 season. The opening of the area to hunting did not cause an additional 56 
per cent of the fall population to die, but only an additional 45.5 per cent. This 
is to be expected because of density dependent factors. 
In contrast, rabbits on the Sanctuary area, which was closed to hunting during 
1961-62, had a probability of dying of only 9 per cent. This figure is based on a 
prehunting estimate of 141 rabbits and a posthunting estimate of 128 rabbits. These 
figures seem to reflect a high rate of survival on the Sanctuary area during the 
past winter. This survival rate may be associated with the relatively lower fall 
population and heavier cover on the Sanctuary area than on the 4-H area. During the 
1960-61 season, when the Sanctuary area was hunted, the probability of dying was 43 
per cent. 
5. Investigations of Furbearers Ralph J. Ellis 
Eye lenses were collected from more than 1,500 raccoons during the past fur 
season. Approximately half of the lenses came from raccoons in the southern hunting 
zone^ the remainder came from the northern hunting zone. These lenses were dried 
and weighed. The ages of the raccoons from which the lenses came were estimated on 
the basis of the lens weight. Knowledge of the age and the approximate date of 
death of each raccoon permitted an estimate of birth dates. 
Table 3.--Mean and modal birth dates of 825 Illinois raccoons born in 1961 and 
examined during the 1961-62 fur season*. 
Northern Zone 
Southern Zone 
Males 
April 15 (201)** 
May 1 (249) 
Mean Birth Date 
Females 
April 27 (191) 
May 13 (134) 
All Raccoons 
April 23 (392) 
May 6 (433) 
Males 
March 9 (201) 
February 23 (249) 
modal Birth Date 
Females 
April 8 (191) 
May 5 (184) 
All Raccoons 
April 8 (392) 
April 18 (433) 
* Birth date estimates were based on age estimate derived from 1 lens weights. 
** Numbers in parentheses indicate sample sizes. 
Table 3 and figure 1 show differences between the birth dates of raccoons of 
different sexes and origins. Only raccoons judged to have been born during 1961 
are represented. Table 3 indicates that the mean birth date of raccoons was earlier 
in the northern hunting zone than in the southern zone. However, figure 1 suggests 
that very early litters are more characteristic of raccoons in the southern zone 
than in the northern zone. Figure 1 also suggests that the births are spread out 
more over the 7 month period in the southern zone than in the northern zone. A 
