Dietary Variation in the Mexican Free-Tailed Bat (Tadarida brasiliensis mexicana)

Abstract

In a field experiment designed to evaluate dietary variation in Mexican free-tailed bats (Tadarida brasiliensis mexicand) we found that lactating females fed largely on coleopter-ans and lygaeid bugs during evening feeding bouts and mostly on moths during morning feeding bouts. These results suggest that interpretations of food habits in this and other species may be biased unless samples from both nightly feeding bouts are included in the analyses. Diets of different individuals during the same feeding bout were strikingly similar, suggesting that lactating females either fed in the same general habitats or that they encountered and preferentially fed on similar prey items among those available. Bats captured upon return from evening feeding bouts produced significantly more fecal pellets than those captured following second feeding bouts. This difference suggests that either more food is eaten in the first feeding bout or, alternatively, highly chitinous insects such as coleopterans and lygaeids contribute more to fecal matter than relatively soft-bodied moths. We found no significant relationship between hardness of prey and number of pellets produced. Individual bats produced an average of 2–3.6 insects/pellet, but no consistent relationship was found between the number of insects eaten and the number of fecal pellets produced. Our analysis indicates that at least five pellets are needed to establish the number of insect taxa (families) consumed by a bat. Results from this study suggests that future research on food habits of insectivorous bats should examine fecal pellets or stomach contents from evening and morning feeding bouts to fully characterize the diet of a given species.