MONTHLY WILDLIFE RESEARCH LETTER 
Vol. 2, No. 9 
Page 2 
remarkably precise although based on a sample of only 223 rabbits. Data from the 
large sample indicated an average monthly prevalence of pregnancy of 0.60 and an 
average monthly litter size of 5.23 which may be compared with 0.59 and 5.58 
obtained in the 1-year study in 1957. The average adult female rabbit that 
survived an entire breeding season produced 22 young. 
May proved to be the month in which the greatest productivity occurred 
because of the large average litter size (6.68 young per pregnant female) and the 
high prevalence of pregnancy (83 per cent). The highest prevalence of pregnancy 
(92 per cent) occurred in March. 
Although reproduction during the first four months of the 1959 breeding 
season was essentially the same as that of last year, the rate during the last 
three months has been so much higher that the total reproductive index for this 
year is 26.66 as compared to 21.08 for last year, an increase of at least 20 
per cent. Yet the principle of inversity appears to be working, for the juvenile 
to adult ratio in August was lower than last year's, and the juvenile ratio in 
September was only 3 per cent higher than last year's. 
W-55-R-4 
This project was inactive during September. 
F. Bellrose 
W-56-R-4 G. Sanderson 
Field work on the raccoon and wood duck study for the past nesting season 
was terminated when active wood duck nesting ceased. The study showed that 29 per 
cent of the natural cavities were used by wood ducks as compared to 51 per cent 
reported for the same region in 1939 and 1940. 
Forty-four per cent of the nests in natural cavities were successful during 
the current study; 49 per cent were successful during the 1939-40 period. When 
both natural cavities and nest boxes were present on the same area, wood ducks 
showed a slight preference for natural cavities. 
Raccoons were responsible for 38 per cent of the nests destroyed during 
the two year period of the current study, but they did not control nesting success. 
Although raccoon populations are at a much higher level and wood duck populations 
lower now than they were during the 1939-40 period of study, they apparently 
destroy no greater percentage of the nests now than they did during the earlier 
period. During the earlier study, 49 per cent of the wood duck nests in natural 
cavities were successful as compared to 44 per cent successful during the present 
study. Fox squirrels destroyed 23 per cent of the unsuccessful nests in natural 
cavities. Nests in the trees banded with "Tanglefoot" were not destroyed by 
raccoons. 
The height to the cavity was important in determining whether a cavity 
would be selected by a wood duck. Cavities from a few feet to 29 feet above 
ground were used less frequently than those 30 feet or more. 
