Growth and Development of Young Pallid Bats, Antrozous pallidus

Abstract

In southern Arizona, young pallid bats are bom in mid-June. the average juvenile has reached the adult range of forearm size by the fifth week of age, and almost all are within adult range by the seventh week. the body weights of the young of both sexes, however, are significantly less than those of the adults until after autumn of the first year, and yearling females weigh significantly less than adults through the autumn of their second year. Development of young pallid bats in wild populations apparently proceeds through several stages at a faster rate than that of young bats reared in captivity. Forearm measurement provides a usable means of estimating ages of the younger bats. by the combined use of forearm measurement and observation of certain developmental stage “check points,” rough estimates of age can be made at least until adult conditions are reached. the use of a checklist of features allows the young of the year to be distinguished from the adults through late fall of the first year. Pallid bats show no sexual dimorphism in forearm lengths, and the young show none in body weight until about the end of the first year of age. Yearling females normally give birth to only one young, whereas most older females give birth to two. Young males are not sexually active in their first autumn and probably not during their first year. Adult females nurse only the young to which they have given birth.