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First published online December 14, 2006
Journal of Experimental Biology 210, 166-176 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02644
Echolocation and passive listening by foraging mouse-eared bats Myotis myotis and M. blythii
1 Laboratorio di Ecologia Applicata, Dipartimento Ar.Bo.Pa.Ve.,
Facoltà di Agraria, Università degli Studi di Napoli Federico
II, via Università 100, I-80055 Portici (Napoli), Italy
2 School of Biological Sciences, University of Bristol, Woodland Road,
Bristol BS8 1UG, UK
3 Zoological Institute, Division of Conservation Biology, University of
Bern, Baltzerstrasse 6, CH-3012 Bern, Switzerland
* Author for correspondence (e-mail: danrusso{at}unina.it)
Accepted 9 November 2006
The two sibling mouse-eared bats, Myotis myotis and M. blythii, cope with similar orientation tasks, but separate their trophic niche by hunting in species-specific foraging microhabitats. Previous work has shown that both species rely largely on passive listening to detect and glean prey from substrates, and studies on other bat species have suggested that echolocation is `switched off' during passive listening. We tested the hypothesis that mouse-eared bats continuously emit echolocation calls while approaching prey. Echolocation may be needed for orientation while simultaneously listening for prey. Because these sibling species forage in different microhabitats and eat different prey, we also compared their echolocation behaviour and related it to their ecology. Both species used echolocation throughout prey approach, corroborating a functional role for echolocation during gleaning. Captive bats of both species emitted similar orientation calls, and pulse rate increased during prey approach. Between the search to approach phases, call amplitude showed a sudden, dramatic drop and bats adopted `whispering echolocation' by emitting weak calls. Whispering echolocation may reduce the risks of masking prey-generated sounds during passive listening, the mouse-eared bats' main detection tactic; it may also avoid alerting ultrasound-sensitive prey. In several cases M. myotis emitted a loud buzz made of 2-18 components when landing. We hypothesise that the buzz, absent in M. blythii at least when gleaning from the same substrate, is used to assess the distance from ground and refine the landing manoeuvre. Our findings have implications for niche separation between sibling species of echolocating bats, support a role for echolocation during passive listening and suggest a functional role for buzzes in landing control.
Key words: bioacoustics, cryptic species, gleaning, mouse-eared bat
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