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    Amazon river dolphins (Inia geoffrensis) use a high-frequency short-range biosonar

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    Date
    2015-10-07
    Author
    Ladegaard, Michael  Concept link
    Jensen, Frants H.  Concept link
    de Freitas, Mafalda  Concept link
    da Silva, Vera Maria F.  Concept link
    Madsen, Peter T.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/7584
    As published
    https://doi.org/10.1242/jeb.120501
    DOI
    10.1242/jeb.120501
    Keyword
     Beamwidth; Clutter; Directionality; Echolocation; Habitat; Toothed whale 
    Abstract
    Toothed whales produce echolocation clicks with source parameters related to body size; however, it may be equally important to consider the influence of habitat, as suggested by studies on echolocating bats. A few toothed whale species have fully adapted to river systems, where sonar operation is likely to result in higher clutter and reverberation levels than those experienced by most toothed whales at sea because of the shallow water and dense vegetation. To test the hypothesis that habitat shapes the evolution of toothed whale biosonar parameters by promoting simpler auditory scenes to interpret in acoustically complex habitats, echolocation clicks of wild Amazon river dolphins were recorded using a vertical seven-hydrophone array. We identified 404 on-axis biosonar clicks having a mean SLpp of 190.3±6.1 dB re. 1 µPa, mean SLEFD of 132.1±6.0 dB re. 1 µPa2s, mean Fc of 101.2±10.5 kHz, mean BWRMS of 29.3±4.3 kHz and mean ICI of 35.1±17.9 ms. Piston fit modelling resulted in an estimated half-power beamwidth of 10.2 deg (95% CI: 9.6–10.5 deg) and directivity index of 25.2 dB (95% CI: 24.9–25.7 dB). These results support the hypothesis that river-dwelling toothed whales operate their biosonars at lower amplitude and higher sampling rates than similar-sized marine species without sacrificing high directivity, in order to provide high update rates in acoustically complex habitats and simplify auditory scenes through reduced clutter and reverberation levels. We conclude that habitat, along with body size, is an important evolutionary driver of source parameters in toothed whale biosonars.
    Description
    Author Posting. © The Company of Biologists, 2015. This article is posted here by permission of The Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 218 (2015): 3091-3101, doi:10.1242/jeb.120501.
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    Suggested Citation
    Journal of Experimental Biology 218 (2015): 3091-3101
     
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