MICROHABITAT USE BY 2 SPECIES OF NYCTOPHILUS BATS - A TEST OF ECOMORPHOLOGY THEORY

The purpose of this study was to measure microhabitat use by light-tag ged foraging Nyctophilus geoffroyi and Nyctophilus gouldi, two at-leas t-partly sympatric species of Australian microchiropteran long-eared b ats. We tested the hypothesis that because of their similar wing morph ology (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 occasionall y flying amongst smaller branches and the vegetation of the forest can opy. We found no statistical difference in the proportion of time spen t in different forest microhabitats by individuals of the two species. Furthermore, on only one occasion did we observe a bat land on the gr ound to forage, despite the fact that both species are described in th e 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 win g form and lend credence to the notion that, at least in some circumst ances, measurements of wing morphology alone can be a useful indicator of the ecology of similar bat species.