Sex and Age Ratios in Wisconsin Muskrats

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Abstract
During the 1946, 1947, and 1948 trapping seasons 24,082 muskrats were examined for sex and age; and during the summers of these yrs. 1149 nestlings were examined for sex. At birth the sex ratio is about even but by the time the young leave the nest the sex ratio is unbalanced to the extent of 140 males per 100 females. This unbalanced condition is maintained through the fall and winter. During the spring and summer the sex ratio in the adult population shifts to a ratio of 98 males per 100 females for the Wis. sample. Age ratios from the different samples varied from 183 young per 100 adults to 673 young per 100 adults and averaged 359 young per 100 adults. A statistical analysis of the data shows an inverse relationship between the density of the breeding population and the survival of the young.

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