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First published online February 27, 2009
Journal of Experimental Biology 212, 823-834 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.022137

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Echolocation by two foraging harbour porpoises (Phocoena phocoena)

Ursula K. Verfuß^1,2,*, Lee A. Miller³, Peter K. D. Pilz² and Hans-Ulrich Schnitzler²

¹ Fjord & Bælt, Margrethes Plads 1, DK-5300 Kerteminde, Denmark
² Tierphysiologie, Zoologisches Institut, Universität Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany
³ Institute of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark

^* Author for correspondence (e-mail: ursula.verfuss{at}meeresmuseum.de)

Accepted 11 December 2008

Synchronized video and high-frequency audio recordings of two trained harbour porpoises searching for and capturing live fish were used to study swimming and echolocation behaviour. One animal repeated the tasks blindfolded. A splash generated by the fish being thrown into the pool or – in controls – by a boat hook indicated prey and stimulated search behaviour. The echolocation sequences were divided into search and approach phases. In the search phase the porpoises displayed a clear range-locking behaviour on landmarks, indicated by a distance-dependent decrease in click interval. Only in trials with fish was the search phase followed by an approach phase. In the initial part of the approach phase the porpoises used a rather constant click interval of around 50 ms. The terminal part started with a sudden drop in click interval at distances around 2–4 m. Close to the prey the terminal part ended with a buzz, characterized by constant click intervals around 1.5 ms. The lag time in the search and the initial part of the approach phase seems to be long enough for the porpoise to process echo information before emitting the next click (pulse mode). However, we assume that during the buzz lag times are too short for pulse mode processing and that distance information is perceived as a `pitch' with a `frequency' corresponding to the inverse of the two-way transit time (pitch mode). The swimming speed of the animal was halved when it was blindfolded, while the click intervals hardly changed, resulting in more clicks emitted per metre swum.

Key words: harbour porpoise, Phocoena phocoena, biosonar, echolocation, foraging behaviour, signal pattern

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