DIETARY VARIATION IN THE MEXICAN FREE-TAILED BAT (TADARIDA-BRASILIENSIS MEXICANA)

In a field experiment designed to evaluate dietary variation in Mexica n free-tailed bats (Tadarida brasiliensis mexicana) we found that lact ating females fed largely on coleopterans and lygaeid bugs during even ing feeding bouts and mostly on moths during morning feeding bouts. Th ese results suggest that interpretations of food habits in this and ot her species may be biased unless samples from both nightly feeding bou ts are included in the analyses. Diets of different individuals during the same feeding bout were strikingly similar, suggesting that lactat ing females either fed in the same general habitats or that they encou ntered and preferentially fed on similar prey items among those availa ble. Bats captured upon return From evening feeding bouts produced sig nificantly more fecal pellets than those captured following second fee ding bouts. This difference suggests that either more food is eaten in the first feeding bout or, alternatively, highly chitinous insects su ch as coleopterans and lygaeids contribute more to fecal matter than r elatively soft-bodied moths. We found no significant relationship betw een hardness of prey and number of pellets produced. Individual bats p roduced an average of 2-3.6 insects/pellet, but no consistent relation ship was found between the number of insects eaten and the number of f ecal pellets produced. Our analysis Indicates that at least five pelle ts are needed to establish the number of insect taxa (families) consum ed ya bat. Results from this study suggests that future research on fo od habits of insectivorous bats should examine fecal pellets or stomac h contents from evening and morning feeding bouts to fully characteriz e the diet of a given species.