Eye lens weight and body size as criteria of age in beaver (Castor canadensis)

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Abstract
Ages of 114 wild-caught beaver (Castor canadensis) had been estimated by cementum layer technique. Relationships between total lens dry weight, body weight, axillary girth, and these estimated ages are described. Total lens dry weight was better than either body weight or axillary girth as a predictor of age. However, none of these criteria, whether used alone or in combination in a multiple regression model, allowed animals more than 1 year old to be placed into year classes with confidence. Linear regression of log10 body weight on log10 axillary girth yielded a slope of 2.0. The discrepancy between this value and slopes obtained for other species may reflect a functional difference in shape and growth of beaver.