We tested the airframes of a community of microbats in terms of flight performance, stability and control, and present the first systematic classification of bat flight manoeuvres. The tail, ears and main-wing all contributed to these airframe functions. In combination, six airframe ratios (aspect ratio, wing loading, tail area ratio, ear area ratio, tail length ratio and ear length ratio) provided robust predictions of species’ foraging microhabitats and foraging strategies (including agility and speed).
SUMMARYWingbeat frequency (fw) and amplitude(θw) were measured for 23 species of Australian bat,representing two sub-orders and six families. Maximum values were between 4 and 13 Hz for fw, and between 90 and 150° forθ w, depending on the species. Wingbeat frequency for each species was found to vary only slightly with flight speed over the lower half of the speed range. At high speeds, frequency is almost independent of velocity. Wingbeat frequency (Hz) depends on bat mass (m, kg) and flight speed (V, ms-1) according to the equation: fw=5.54-3.068log10m-2.857log10V. This simple relationship applies to both sub-orders and to all six families of bats studied. For 21 of the 23 species, the empirical values were within 1 Hz of the model values. One species, a small molossid, also had a second mode of flight in which fw was up to 3 Hz lower for all flight speeds.The following relationship predicts wingbeat amplitude to within±15° from flight speed and wing area (SREF,m2) at all flight speeds:θ w=56.92+5.18V+16.06log10SREF. This equation is based on data up to and including speeds that require maximum wingbeat amplitude to be sustained. For most species, the maximum wingbeat amplitude was 140°.
Airframe design parameters related to flight performance, stability and control had tight, functionally appropriate relationships with the foraging niches and echolocation parameters of nine species comprising the bat fauna of the Little Sandy Desert, Australia. The airframe parameters segregated into two near-independent groups, one related to microhabitat use, the other to foraging strategy. The structure of the desert's bat fauna is displayed in these terms, and its organisation is compared with the faunas of surrounding regions. A diversity–productivity model of faunal structure is revealed, with an organisation that conforms with the 'specialisation' hypothesis. Clear family-level relationships between phylogeny and foraging ecology imply that ecological specialisations occurred early in the evolution of bats.
-Between 2004 and 2007, we systematically surveyed microbats across the Pilbara region in Western Australia, and collected data on species' foraging ecology. Here we report the results of the echolocation survey of 69 sites dispersed among 24 survey areas covering the 179,000 km 2 region. Echolocation call sequences were identifi ed using a library of known calls accumulated during fi eld work. In combination, the frequency maintained for the greatest number of cycles (F peakC ) and the bandwidth ratio of this peak (Q) identifi ed search-mode echolocation calls by 13 of the 17 species comprising the microbat fauna of the Pilbara bioregion. These variables did not separate Taphozous georgianus from T. hilli calls, Chalinolobus gouldii from Mormopterus loriae, and allopatric pairs of Nyctophilus species. Even so, the spectral characters provided an ecologically informative, viable and non-intrusive survey tool. The survey revealed two compositionally distinct communities. One comprised 14 species and occupied landward environments, while the other comprised 9 species and occupied mangroves. Three members of the mangrove community were confi ned to mangroves (M. loriae, Nyctophilus arnhemensis and N. geoffroyi pallescens), being replaced by allopatric congenerics in the region's landward environments (Mormopterus beccarii, Nyctophilus bifax daedalus and N. g. geoffroyi). In both communities, the searchmode calls of syntopic species were dispersed in spectral space, showed only peripheral overlap in their spectral variables (Q and F peakC ) and were arrayed according to differences in foraging niche determined from empirical data on species' fl ight capabilities and foraging behaviours. These observations imply a niche-assembly model of metacommunity structure. However, on its own, this model was insuffi cient to explain the composition of the Pilbara microbat assemblages. Nestedness was observed in assemblage composition that could be explained by environmental factors, implying the infl uence of environmental controls. The richest microbat assemblages were recorded in well-developed riparian environments with complex vegetation structures and permanent pools that were set in cavernous landscapes. Two species (Nyctophilus bifax and Chalinolobus morio) were restricted to these productive riparian environments, while two others (Macroderma gigas and Rhinonicteris aurantia) were found to be more common than previously supposed despite detectability constraints caused by their cryptic calls. The widespread occurrence of M. gigas and R. aurantia is reasonable because caves and mines are common in the ranges of the Pilbara region, and offer physiologically favourable day-roosts to these otherwise mesic tropical species. Proximity of cavernous landscapes also explained the presence or absence of other obligate cave/rock-crevice roosting species in assemblages (Taphozous spp., and Vespadelus fi nlaysoni). Comparison with surrounding regions revealed a diversity-productivity model of faunal structure, with an organ...
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 (m bat ) and aligned into three statistically distinct classes that relate foraging strategy with morphology when plotted against m bat . 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.
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