The Pelt-Primeness Method of Aging Muskrats

Abstract

In a search for a rapid and reliable criterion of age by which mass data on age composition of muskrat populations could be obtained, 1,070 muskrat pelts were examined. Sex was detd. by the presence or absence of mammae. Two distinct patterns of primeness were found: the symmetrical pattern of the juveniles and the asymmetrical pattern of the adults. Of 208 animals live-trapped, tagged, and released, 69 were retaken during the following winter and examination of their pelts showed this method to be 93% accurate. To compare the accuracy of the pelt-primeness method with other methods in use, 455 freshly trapped muskrats were also classified by the following 3 methods: appearance of the external genitalia, inspection of the reproductive tracts, and pelt length. Pelt length was not found to be reliable. Dis-crepencies between the pelt primeness method and the reproductive tract inspection method may result from young animals which breed during their first summer. In these animals, an autopsy in the fall reveals a juvenile pattern of primeness and placental scars. By means of pelt inspection the age and sex composition of several thousand muskrats can be detd. in a single day.