Prey selection by insectivorous bats: are essential fatty acids important?

Abstract

Although body temperatures of torpid animals fall well below the melting point of many fats, body fats must remain fluid to be metabolized. High levels of dietary essential fatty acids (EFAs) may facilitate the use of torpor, as an increase in the proportion of EFAs in body fat decreases the melting point of body fats. The purpose of our study was to determine the importance of EFAs in the diets of four reproductive classes (males and nonreproductive pregnant, and lactating females) of three species of insectivorous bats: Myotis yumanensis, M. lucifugus, and M. californicus. Males are expected to use torpor frequently and, therefore, should select a diet high in EFAs. We ranked insect orders found in bat feces (diet) and light-suction-trap samples (availability) on the basis of their linoleic acid (a common EFA) content. We used these ranks to obtain estimates of the linoleic acid content of bats' diets, i.e., "dietary fat scores," and of available insects' "trap sample fat scores," respectively. Dietary fat scores did not differ significantly among reproductive classes. As predicted, the average fat score of males was high relative to the fat score of available insects. However, fat scores of male M. lucifugus and M. yumanensis were significantly greater than those of male M. californicus. Thus, EFAs do not appear to be as important in the diet of the latter species, suggesting that torpor may not be employed regularly.