Date of Award

Spring 1990

Document Type


Degree Name

Master of Science (MS)


Biological Sciences



Committee Director

Robert K. Rose

Committee Member

Frank P. Day, Jr.

Committee Member

John Holsinger

Committee Member

Mark Butler

Call Number for Print

Special Collections LD4331.B46 M335


Reproductive status in specimens of nine populations of seven species of small mammals was evaluated by examining the external reproductive features of nipple size, condition of the pubic symphysis, and vaginal condition and, in males, testis position. Usefulness of these external features in predicting true monthly breeding rates was evaluated by comparing predictions of breeding rates with true rates based on necropsy. Accuracy of predictions of reproductive status of individuals based on single external features and combinations of external features and body measurements was then analyzed at a finer level by comparing those predictions with results of necropsy of the same animals.

Testis position was a more accurate indicator of true breeding rates than were the female external features. It may be that testis position is easier to evaluate than are the female external features, or that testis position is more closely linked temporally to spermatogenesis than are nipple size or condition of the pubic symphysis to pregnancy. Nipple size was the best predictor among females.

Accuracy of predictions of reproductive status of individuals based on individual external features ranged from 58-85% correct for females, and from 87-944 correct for males. Female predictors were more accurate in seasonal northern populations than in continuously breeding populations. Breeding status of truly non-breeding animals was more accurately predicted in the non-breeding season, while breeding animals were better predicted in the breeding season. Predictive equations generated with logistic multiple regression analysis produced substantial improvement in accuracy of predictions of true reproductive status in females of three species from Manitoba, Canada.

Results confirm the usefulness of testis position as a predictor of reproduction, and also affirm that nipple size is the most useful female variable. In females, the inclusion of body weight, more than body length, in a predictive equation may significantly improve predictive usefulness, especially in small-bodied species with relatively great weight gains at pregnancy.


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