An Analysis of External Features as Predictors of Reproductive Status in Small Mammals

Abstract

External reproductive features are frequently used as indicators of the reproductive status of small mammals, but the extent to which these external features correctly indicate reproductive status is poorly known. We evaluated the validity of the external reproductive features of nipple size, vaginal condition, condition of the pubic symphysis, and position of the testes in predictions of reproductive status based on necropsy of individuals of nine populations of seven species of small mammals. Results showed that testis position is a relatively accurate predictor of reproductive status in males (87–94%), but that the external features of females are less accurate and consistent (58–85%), with nipple size being best. Predictive equations produced by logistic multiple regression analysis, using combinations of external reproductive features and body measurements, produced no significant improvement in accuracy of predictions in males, but significant improvements were obtained in analyses of data from females of three species of small mammals from Manitoba, Canada. We suggest that the use of body weight with external reproductive features in predictive equations will improve the accuracy of predictions of the reproductive status of small, seasonally breeding species.