[MARMAM] New publication: Heaviside's dolphins (Cephalorhynchus heavisidii) relax acoustic crypsis to increase communication range

Morgan J. Martin mjmartin at sandiego.edu
Thu Jul 19 01:09:38 PDT 2018

Dear Colleagues,

We are pleased to announce our recent publication on Heaviside's dolphin
acoustic signals in the Proceedings of the Royal Society B:

* Martin MJ, Gridley T, Elwen SH, Jensen FH. (2018) Heaviside’s dolphins
(Cephalorhynchus heavisidii) relax acoustic crypsis to increase
communication range. Proc. R. Soc. B 285: 20181178.
<http://dx.doi.org/10.1098/rspb.2018.1178> *

The costs of predation may exert significant pressure on the mode of
communication used by an animal, and many species balance the benefits of
communication (e.g. mate attraction) against the potential risk of
predation. Four groups of toothed whales have independently evolved
narrowband high-frequency (NBHF) echolocation signals. These signals help
NBHF species avoid predation through acoustic crypsis by echolocating and
communicating at frequencies inaudible to predators such as mammal-eating
killer whales. Heaviside's dolphins (*Cephalorhynchus heavisidii*) are
thought to exclusively produce NBHF echolocation clicks with a centroid
frequency around 125 kHz and little to no energy below 100 kHz. To test
this, we recorded wild Heaviside's dolphins in a sheltered bay in Namibia.
We demonstrate that Heaviside's dolphins produce a second type of click
with lower frequency and broader bandwidth in a frequency range that is
audible to killer whales. These clicks are used in burst-pulses and
occasional click series but not foraging buzzes. We evaluate three
different hypotheses and conclude that the most likely benefit of these
clicks is to decrease transmission directivity and increase conspecific
communication range. The expected increase in active space depends on
background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz
Sea State 1) the active space of NBHF signals. This dual click strategy
therefore allows these social dolphins to maintain acoustic crypsis during
navigation and foraging, and to selectively relax their crypsis to
facilitate communication with conspecifics.

This paper can be accessed at: http://rspb.royalsocietypublishing.org/

Please contact me if you would like a PDF copy. Happy reading!

Sincerely and on behalf of all authors,

Morgan J. Martin
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