Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocoena phocoena)

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Abstract

Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking.

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Danuta M Wisniewska

Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark

For correspondence
danuta.wisniewska@bios.au.dk

Competing interests
The authors declare that no competing interests exist.
John M Ratcliffe

Sound and Behaviour Group, Institute of Biology, University of Southern Denmark, Odense, Denmark

Competing interests
The authors declare that no competing interests exist.
Kristian Beedholm

Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark

Competing interests
The authors declare that no competing interests exist.
Christian B Christensen

Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark

Competing interests
The authors declare that no competing interests exist.
Mark Johnson

Scottish Oceans Institute, University of St Andrews, St Andrews, Scotland

Competing interests
The authors declare that no competing interests exist.
Jens C Koblitz

Animal Physiology, Institute for Neurobiology, University of Tübingen, Tübingen, Germany

Competing interests
The authors declare that no competing interests exist.
Magnus Wahlberg

Sound and Behaviour Group, Institute of Biology, University of Southern Denmark, Odense M, Denmark

Competing interests
The authors declare that no competing interests exist.
Peter T Madsen

Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark

Competing interests
The authors declare that no competing interests exist.

Ethics

Animal experimentation: The animals are maintained by Fjord&Belt, Denmark, under permits no. SN 343/FY-0014 from the Danish Ministry of Food, Agriculture and Fisheries, and 1996-3446-0021 from the Danish Forest and Nature Agency (under the Danish Ministry of the Environment). Their care and all experiments are in strict accordance with the recommendations of the Danish Ministry of Food, Agriculture and Fisheries (issuing the permit to keep the animals), the Danish Ministry of the Environment (permit for catching the animals) and the Danish Council for Experiments on Animals (always contacted for permits when appropriate - but in the case of this study such permit was not required).

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.