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The activity levels of seven species of insectivorous microbats in five habitats widespread across the Charles Darwin Reserve in the Murchison region of Western Australia were measured using echolocation detectors and compared with results of habitat usage revealed by stable isotope analysis. The activity levels were further compared with projective foliage density as a surrogate of productivity within each habitat. Habitat use, estimated from echolocation activity of the microbat species and from stable isotope analysis of their fur, agree and each provides complementary information on the habitats preferred by species. Both methods show that five of the species, Chalinolobus gouldii, C. morio, Mormopterus species 3, Nyctophilus geoffroyi and Tadarida australis, are active and forage over each of the five habitats. Scotorepens balstoni is shown by both methods to prefer habitats with C3 woodland over C4 shrubs and grasses. Vespadelus baverstocki is shown by both methods to fly and forage over habitats with developed arid-zone shrubland understorey vegetation. The echolocation method shows that bat activity levels align with the foliage mass of the vegetation as measured by the projected foliage density. The species’ stable isotope signatures show that the insects captured are feeding primarily on the ground cover of the habitats. The two species that have high δC signatures, S. balstoni and V. baverstocki, are shown to be most active in habitats with a C4 ground cover.

The microbat assemblage on Charles Darwin Reserve was investigated between 2007 and 2009 to provide a benchmark for monitoring long-term responses to climate change on a major bioregional boundary, the mulga–eucalypt line. Stable isotope analysis of bat fur was used to interpret the current local habitat and trophic relationships between microbat species with different biogeographical affinities. The stable isotope values of the ants inhabiting 10 broad vegetation types were used to provide an isotopic baseline of the Reserve to assist in the interpretation of the δC or δN signatures observed in the bat assemblage. The δC signatures of ants in both a Salmon Gum woodland and an arid shrubland shifted significantly after the breaking of a prolonged drought but there was no change in the bats. The ubiquitous bat species, and those with south-western affinities, probably used most of the available vegetation types on the Reserve and displayed some significant differences in mean trophic level. Scotorepens balstoni, a species of the southern interior of Western Australia, specialised at foraging within patches of eucalypt woodland. Vespadelus baverstocki, a southern arid zone species, was evidently restricted to the proximal arid habitats with distinctively high δN signatures.

The Australian bat Tadarida australis has a peculiar geographical niche that involves a continental-scale movement of over 10 of latitude in Western Australia. Its range expands northward by up to 1200 km for the winter and contracts southward for the summer. Its summer range limit correlates with an interaction of temperature and humidity, best summarised by atmospheric enthalpy. Its winter distribution is expanded northward within the enthalpy threshold, but appears to be further restricted in some areas by an unknown factor that may be biotic. We propose a potential competitor and a potential predator that may have strongly negative interactions in these regions. The 1% of records that are beyond the enthalpy envelope are from the change-over months and may be an artefact of year-to-year climatic variation. Three climatic thresholds enclose the enthalpy envelope: average annual rainfall >10 mm per month and <50 mm per month, and average overnight minimum temperature <20C. Current literature relates migration of temperate-zone bats to resource availability as a consequence of changing season. We identify a tight correlation with atmospheric enthalpy that points to dissipation of flight muscle heat as a limiting factor.

The primary flight muscles of the chest, shoulder, back and upper arms were weighed for 29 species of Australian bat, representing two suborders and six families. Values of muscle masses were found to be between 9 and 23% of the mass of the bat (mbat) and aligned into three statistically distinct classes that relate foraging strategy with morphology when plotted against mbat. These classes represent 'high-energy', 'general' and 'low-energy' foraging strategies. The above relationships were visible in both the wing downstroke and upstroke muscle groups, but not in the shoulder and elbow flex/extend groups. Differences in the foraging ecologies and geographical distributions of Western Australian bats are reflected in 'flight motor power output' as well as the bats' 'airframe design' attributes. Based on these attributes and ecologies, a method is presented for estimating the mass of flight muscle.