EFFECT OF CLIMATIC VARIATION ON REPRODUCTION BY PALLID BATS (ANTROZOUS-PALLIDUS)

Bats are unusual among mammals in having the ability to respond to fluctuating climatic conditions by employing either a homeothermic or a heterothermic strategy. Low temperatures affect insectivorous bats by increasing the energy required for homeothermy while roosting and by decreasing the energy available due to lower activity of insect prey. Low temperatures may be particularly costly to pregnant and lactating bats because these experience greater energetic demands due to gestation and milk production. The use of heterothermy may increase gestation length and decrease milk production. In a 2-year study of female pallid bats (Antrozous pallidus) in central Oregon, I found that lower spring temperatures in 1991 than in 1990 were correlated with a higher percentage of nonreproductive females, delayed parturition dates, reduced synchrony of parturition, and lower body mass of lactating females. Overall reproductive success was probably lower in 1991 as a result of females not reproducing or of juvenile mortality. In 1991, both females and juveniles were probably in poorer condition prior to migrating and entering hibernation. The effects of temperature on reproduction in this ground-foraging bat are similar to those documented for aerial insectivorous bats. These results have implications for conservation and management of this species in the northern part of its range.