[MARMAM] New publication: Context-dependent biosonar adjustments during active target approaches in echolocating harbour porpoises
michael.ladegaard at bios.au.dk
Wed Aug 21 05:16:28 PDT 2019
It is my pleasure to announce a new biosonar publication, where Peter Madsen and I show how harbour porpoises use different biosonar behaviours depending on the context in which they are echolocating:
Context-dependent biosonar adjustments during active target approaches in echolocating harbour porpoises
Michael Ladegaard, Peter Teglberg Madsen
Journal of Experimental Biology 2019 222: jeb206169 doi: 10.1242/jeb.206169 Published 19 August 2019
In this study, we had two free-swimming porpoises approach the same target over the same approach distance in two highly different environments: a shallow-water pvc-lined pool and a semi-natural harbour net pen. In the confined pool environment, the porpoises showed a higher degree of range-dependent adjustment to the target and used lower source levels (SLs) and shorter interclick intervals (ICIs) compared to the net pen. The ambient noise at the high frequencies relevant for porpoise echolocation was low in both environment, so the porpoises likely changed echolocation behaviour in response to the different reverberant conditions between the two environments. Our study highlight that porpoises approaching a specific echolocation target not only use range-dependent, but also context-dependent biosonar adjustments, thus underscoring the flexibility of toothed whale biosonar.
The paper was published in Journal of Experimental Biology and may be downloaded here:
It is also featured in an Inside JEB article here:
In case you cannot access the paper through the JEB website then please send me an email and I will be happy to share a download link with you.
All the best,
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Echolocating mammals generally target individual prey items by transitioning through the biosonar phases of search (slow-rate, high-amplitude outputs), approach (gradually increasing rate and decreasing output amplitude) and buzzing (high-rate, low-amplitude outputs). The range to the main target of interest is often considered the key or sole driver of such biosonar adjustments of acoustic gaze. However, the actively generated auditory scene of an echolocator invariably comprises a large number of other reflectors and noise sources that likely also impact the biosonar strategies and source parameters implemented by an echolocating animal in time and space. In toothed whales, the importance of context on biosonar adjustments is largely unknown. To address this, we trained two harbour porpoises to actively approach the same sound recording target over the same approach distance in two highly different environments: a PVC-lined pool and a semi-natural net pen in a harbour, while blind-folded and wearing a sound recording tag (DTAG-4). We show that the approaching porpoises used considerably shorter interclick intervals (ICIs) in the pool than in the net pen, except during the buzz phase, where slightly longer ICIs were used in the pool. We further show that average click source levels were 4–7 dB higher in the net pen. Because of the very low-level in-band ambient noise in both environments, we posit that the porpoises adapted their echolocation strategy to the different reverberation levels between the two settings. We demonstrate that harbour porpoises use different echolocation strategies and biosonar parameters in two different environments for solving an otherwise identical target approach task and thus highlight that biosonar adjustments are both range and context dependent.
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