An acoustic survey of zoophagic bats on islands in the Kimberley, Western Australia, including data on the echolocation ecology, organisation and habitat relationships of regional communities

Abstract

Bat ultrasound was recorded on 30 of the in-shore islands along the Northern Kimberley coast as part of a biological survey to assess their conservation potential as microcosms of the region’s biodiversity. Species were identifi ed from their search-mode echolocation call sequences using a call library based (mainly) on two variables: the frequency maintained for the greatest number of cycles (FpeakC) and sharpness quotient (Q). Populations of 20 of the 21 species that comprise the Northern Kimberley region’s zoophagic bat fauna are now known to occur on these islands, an average of 8±0.6 (S.E.) species per island. The Kimberley has two compositionally distinct bat communities, one occupying landward environments and the other occupying mangroves. Both were represented on the islands. In each community, the search-mode calls of syntopic species were dispersed in spectral space, with few showing more than peripheral overlap in their spectral variables (Q and FpeakC). Their different call designs were functionally appropriate to differences in (1) foraging niche predicted from empirical data on species’ fl ight capabilities and foraging behaviours, and (2) airframe variables related to fl ight performance and control. These observations imply a niche-assembly model of metacommunity structure. Pleistocene climatic fluctuations and habitat filtering also appear to have influenced metacommunity structure at regional scales. However, nestedness was observed in assemblage composition that could be explained by environmental factors, implying the infl uence of environmental controls. The richest bat assemblages were recorded on the most mesic of the large inshore islands with cavernous landscapes and permanent pools. Comparison with surrounding regions revealed a diversity-productivity model of faunal structure, with an organisation that conforms to the specialisation hypothesis. Six islands, including their mangrove stands, are identified as priorities for conservation.