Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Proceedings of the Royal Society B. Biological Sciences 285 (2018): 20181178, doi:10.1098/rspb.2018.1178.
Description:
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.
Description:
This research was supported by a Fulbright U.S. Research Fellowship, the National Geographic
Society’s Emerging Explorers Grant in conjunction with the Waitt Foundation (38115) and the
University of Pretoria’s Zoology Department. TG was funded by the Claude Leon Foundation,
and SE was funded by the South African National Research Foundation. FHJ acknowledges
funding from the Office of Naval Research (N00014-1410410) and an AIAS-COFUND
fellowship from Aarhus Institute of Advanced Studies.
Keywords:
Acoustic crypsis
;
Active space
;
Communication
;
Echolocation
;
Heaviside’s dolphin
;
Narrowband high-frequency clicks
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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