Microhabitat Use by Two Species of Nyctophilus Bats: a Test of Ecomorphology Theory

Abstract

The purpose of this study was to measure microhabitat use by light-tagged foraging Nyctophilus geoffroyi and Nyctophilus gouldi, two at-least-partly sympatric species of Australian microchiropteran long-eared bats. We tested the hypothesis that because of their similar wing morphology (low wing loading and aspect ratio) and echolocation-call design (high-frequency, frequency-modulation calls), the two species’ choice of foraging microhabitat should be similar. Our results showed that, typically, individuals of both species flew relatively slowly in large circles approximately 2–5 m above the ground and below the canopy but amongst the trunks of forest trees, with some individuals occasionally flying amongst smaller branches and the vegetation of the forest canopy. We found no statistical difference in the proportion of time spent in different forest microhabitats by individuals of the two species. Furthermore, on only one occasion did we observe a bat land on the ground to forage, despite the fact that both species are described in the literature as substrate gleaners. We also found no evidence for any change in habitat use with changing lunar condition. Our data support ecomorphological predictions generated from simple measurements of wing form and lend credence to the notion that, at least in some circumstances, measurements of wing morphology alone can be a useful indicator of the ecology of similar bat species.