Presumably, reproductive female bats are more constrained by thermoregulatory and energy needs than are males and nonreproductive females. Constraints imposed on reproductive females may limit their geographic distribution relative to other bats. Such constraints likely increase with latitude and elevation. Males of 11 bat species that inhabit the Black Hills were captured more frequently than females, and reproductive females typically were encountered at low-elevational sites. To investigate the relationship between female distribution and elevation, we fitted a logistic regression model to evaluate the probability of reproductive-female capture as a function of elevation. Mist-net data from 1,197 captures of 7 species revealed that 75% of all captures were males. We found a significant inverse relationship between elevation and relative abundance of reproductive females. Relative abundance of reproductive females decreased as elevation increased. Reproductive females may be constrained from roosting and foraging in high-elevational habitats that impose thermoregulatory costs and decrease foraging efficiency. Failure to account for sex differences in distributional patterns along elevational gradients may significantly bias estimates of population size.