Bat folivory in numbers: how many, how much, and how long?

Abstract

Folivory in bats has been described as chewing bits of leaves to extract the liquids, and then discarding the remaining fibers in form of oral pellets. At least eight species of Neotropical fruit-eating bats have been reported to use folivory as a strategy potentially to provide bats with vitamins, micronutrients and proteins usually scarce in fruits, as well as secondary metabolites that stimulate or inhibit reproductive processes, or even as a supply of water. All reported cases of folivory in bats consist of short, descriptive natural history notes with few supporting details. In depth understanding of leaf consumption by bats is lacking. To bridge this gap, we studied two colonies of Artibeus living under different conditions in the Venezuelan Andes: an urban colony (A. lituratus) and a forest colony (A. amplus) whose individuals exhibited folivorous habits. We hypothesized that bats: (1) feed on leaves from many plant species, and more frequently eat certain plant species over others, (2) show monthly variation in leaf consumption, (3) eat specific parts of each leaf and discard the rest, and (4) within a plant species, eat the same part of each leaf. We collected leaves found below the roosting site of the colonies of both species and analyzed digital images of each leaf to quantify the consumed area. All leaves (n = 1,188) were classified and quantified in terms of the pattern of observed consumption (apical, basal, other). We found that both species of bats fed on leaves from certain plant species over others, showed monthly variation in leaf consumption, and on average consumed less than 50% of the leaf, equivalent to an area of 5–7 cm2 (n = 655). Maximum consumption of leaves was observed in both species in the weeks immediately prior to males exhibiting scrotal testes and females becoming palpably pregnant. Results from our study provide the first systematic and detailed assessment of folivory in bats, showing the use of leaves all year long by two bat species. Future research should investigate whether males and females consume leaves to the same extent, and on the chemical properties of consumed plant species.