Meike Linnenschmidt, Laura N. Kloepper, Magnus Wahlberg & Paul E. Nachtigall
(2012): Stereotypical rapid source level regulation in the harbour porpoise
biosonar. Naturwissenschaften 99 (9), 767-771.
Abstract: Some odontocetes and bats vary both click intensity and receiver
sensitivity during echolocation, depending on target range. It is not known how
this so-called automatic gain control is regulated by the animal. The source
level of consecutive echolocation clicks from a harbour porpoise was measured
with a hydrophone array while the animal detected an aluminium cylinder at 2, 4
or 8 m distance in a go/no-go paradigm. On-axis clicks had source levels of
145–174 dB re 1 μPa peak-to-peak. During target-present trials the click trains
reached comparable source levels independent of the range to the target after
three clicks. After an additional click, the source level was reduced for the 2
and 4 m trials until it equalled the one-way transmission loss. During
target-absent trials, the source level remained high throughout the entire
click train. Given typical values of harbour porpoise inter-click intervals,
the source level reduction commenced within a few 100 ms from the first click
in the click train. This may indicate a sub-cortically regulated source level
regulation in the harbour porpoise.
Kind regards
Sonja Amoser
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Dr. Sonja Amoser
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