Composition and temporal variation in the diet of intermediate horseshoe bat, Rhinolophus affinis, relative to insect abundance in a tropical rainforest environment of Southeast Asia

Abstract

Dietary studies on insectivorous bat species in Southeast Asia are relatively few. We studied diet of the intermediate horseshoe bat, Rhinolophus affinis, and the temporal variations in prey resource use. We also measured prey availability in order to explore whether this species is a generalist or specialist feeder. A total of 665 fecal samples were collected from 133 captured individuals from January to December 2019 in a tropical rainforest of Penang Island (Malaysia). A descriptive analysis of samples revealed a total of eight insect prey orders. The main taxon was Coleoptera (Percent Volume >50%), followed by Isoptera, Hemiptera, Lepidoptera, Hymenoptera and Diptera, respectively (5–15%). Neuroptera and Psocoptera were occasionally found in the samples (each <1%). This result exhibits a degree of dietary specialization on coleopterans although the diet composition was flexible and significantly varied over time (among months and within nights). Based on light trapping, Coleoptera, Hemiptera, Lepidoptera, Hymenoptera and Diptera were frequent insects in the study area, while Isoptera was seasonally abundant. The correlation between variation in the diet and light trap for each prey taxon was mostly not statistically significant, suggesting that R. affinis do not consume prey in proportion to abundance and alternatively may discriminate between prey items when foraging and take prey in rank order. Given this, we further investigated the heavy consumption of absolute abundance of Coleoptera (high‐ranking prey in diet). As a result, coleopterans were included in the diet regardless of the abundance of other prey showing a pattern of dietary specialization.