[MARMAM] Toothed whale biosonar beams: from flashlight to floodlight
Peter Teglberg Madsen
peter.madsen at bios.au.dk
Tue May 12 02:10:08 PDT 2015
For those of you interested in echolocation, we have two recent papers out showing that toothed whales can change the width of their biosonar beams adaptively to the sonar task at hand. At close range they broaden their acoustic field of view likely to minimize the risk that prey escapes, while at longer ranges a narrow beam may reduce clutter problems.
Please find abstracts below. Requests for pdf's can be made to the first authors:
Danuta Wisniewska: danuta.wisniewska at bios.au.dk<mailto:danuta.wisniewska at bios.au.dk>
Frants Jensen: fjensen at princeton.edu<mailto:fjensen at princeton.edu>
Peter T. Madsen
Zoophysiology, Department of Bioscience
Aarhus University, Build. 1131, CF Mollers Alle
8000 Aarhus C, Denmark
Phone: 0045 8715 6501
email: peter.madsen at biology.au.dk<mailto:peter.madsen at biology.au.dk>
Range-dependent flexibility in the acoustic field of view of echolocating porpoises (Phocoena phocoena)
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.
Single-click beam patterns suggest dynamic changes to the field of view of echolocating Atlantic spotted dolphins (Stenella frontalis) in the wild
Echolocating animals exercise an extensive control over the spectral and temporal properties of their biosonar signals to facilitate perception of their actively generated auditory scene when homing in on prey. The intensity and directionality of the biosonar beam defines the field of view of echolocating animals by affecting the acoustic detection range and angular coverage. However, the spatial relationship between an echolocating predator and its prey changes rapidly, resulting in different biosonar requirements throughout prey pursuit and capture. Here we measured single click beam patterns using a parametric fit procedure to test whether free-ranging Atlantic spotted dolphins (Stenella frontalis) modify their biosonar beamwidth. We recorded echolocation clicks using a linear array of receivers and estimated the beamwidth of individual clicks using a parametric spectral fit, cross-validated with well-established composite beam pattern estimates. The dolphins apparently increased the biosonar beamwidth, to a large degree without changing the signal frequency, when they approached the recording array. This is comparable to bats that also expand their field of view during prey capture, but achieve this by decreasing biosonar frequency. This behaviour may serve to decrease the risk that rapid escape movements of prey take them outside the biosonar beam of the predator. It is likely that shared sensory requirements have resulted in bats and toothed whales expanding their acoustic field of view at close range to increase the likelihood of successfully acquiring prey using echolocation, representing a case of convergent evolution of echolocation behaviour between these two taxa.
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