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Echolocation by Insect-Eating Bats

[ "Hans-Ulrich Schnitzler () is professor and head of the Lehrstuhl Tierphysiologie of the University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany."]; [ "Elisabeth Kalko is professor and head of the Abteilung Experimentelle Ökologie of the University of Ulm, Albert Einstein Allee 11, D89069 Ulm. E. Kalko is a staff member and H.-U. Schnitzler is a research associate of the Smithsonian Tropical Research Institute, Panama. E. Kalko is also a research associate at the National Museum of Natural History in Washington, DC."]
BioScience (Impact Factor: 5.44). 09/2009; DOI: 10.1641/0006-3568(2001)051[0557:EBIEB]2.0.CO;2
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    ABSTRACT: Behavioural flexibility: the little brown bat, Myotis lucifugus, and the northern long-eared bat, M. septentrionalis, both glean and hawk prey We present behavioural data demonstrating that the little brown bat, Myotis lucifugus, and the northern long-eared bat, M. septentrionalis, can glean prey from surfaces and take prey on the wing. Our data were collected in a large outdoor flight room mimicking a cluttered environment. We compared and analysed flight behaviours and echolocation calls used by each species of bat when aerial hawking and gleaning. Our results challenge the traditional labelling of M. lucifugus as an obligate aerial-hawking species and show that M. septentrionalis, which is often cited as a gleaning species, can capture airborne prey. As has been shown in previous studies, prey-generated acoustic cues were necessary and sufficient for the detection and localization of perched prey. We argue that the broadband, high-frequency, downward-sweeping, frequency-modulated calls used by some bats when gleaning prey from complex surfaces resolve targets from background. First, because calls of lower frequency and narrower bandwidth are sufficient for assessing a surface before landing, and second, because there are few, if any, simple surfaces in nature from which substrate-gleaning behaviours in wild bats would be expected.  2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The foraging strategies used to obtain prey, like preferred prey type, are used to classify predatory animals. For example, the northern pike, Esox lucius, is an ambush predator capable of bursts of speed when attacking prey that pass close by its hidden position. Behavioural observations of individuals capturing prey corroborate physiological observations of neuromuscular, biome-chanical and cardiovascular systems indicating that ambush is how pike catch their prey (Ahlborn et al. 1997). Furthermore, through foraging strategy specializ-ation, sensory systems have evolved in a complementary fashion: it is no coincidence that raptors have remarkable visual acuity (Reymond 1985). The little brown bat, Myotis lucifugus, has traditionally been labelled an aerial-hawking species (e.g. Barclay 1991), and the northern long-eared bat, Myotis septentrionalis, a gleaning species (e.g. Foster & Kurta 1999). However, anecdotal evidence suggests that M. lucifugus can take prey from surfaces (Simmons & Stein 1980) and that M. septentrionalis captures airborne prey (Miller & Treat 1993). These 5–8-g Nearctic insectivorous species are sympatric over much of their range, share a similar diet, and are often found together at night roosts and hibernacula (Barclay & Fenton 1980; Caceres & Barclay 2000). Both species are commonly observed flying within cluttered habitats (van Zyll de Jong 1985). On inspection of live individuals, these species can be difficult to distinguish (van Zyll de Jong 1985), although the ears and tragi of M. septentrionalis are longer than those of M. lucifugus (Caceres & Barclay 2000). Norberg & Rayner's (1987) ecological morphology model categorizes them together as species that will fly slowly and be highly manoeuvrable and thus well suited to foraging in cluttered environments. The echolocation calls used by M. septentrionalis while gleaning prey are reported to be of shorter duration (which prevents pulse-echo overlap at short distances), higher peak frequency (which should provide higher resolution of small objects as a result of shorter wave-length) and broader bandwidth (greater frequency range, greater resolution) than the echolocation calls used by M. lucifugus (Faure et al. 1993). However, in Faure et al.'s study, the calls used by M. septentrionalis during gleaning were compared to the search calls of M. lucifugus. The echolocation call sequences produced by M. lucifugus dur-ing aerial attacks on airborne, insect prey are among the first recorded for any bat species and are used to describe
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    Acta Chiropterologica 12/2013; 15(2):431–439. · 0.89 Impact Factor

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