[MARMAM] New publication: Commerson's dolphins can relax acoustic crypsis

Morgan J. Martin mjmartin at sandiego.edu
Tue Jun 22 13:32:04 PDT 2021

Dear All,

On behalf of my co-authors, I am pleased to announce the publication of our
new paper, "Commerson’s dolphins (*Cephalorhynchus commersonii*) can relax
acoustic crypsis".

Morgan J. Martin, Sara Torres Ortiz, M. Vanesa Reyes Reyes, Alexander
Marino, Miguel Iñíguez Bessega, & Magnus Wahlberg (2021). Commerson’s
dolphins (*Cephalorhynchus commersonii*) can relax acoustic crypsis.
Ecology and Sociobiology*, 75(6), 100. doi:10.1007/s00265-021-03035-y

Toothed whales use powerful ultrasonic biosonar pulses (i.e. clicks) for
echolocation. Underwater acoustic recordings have suggested that the
majority of toothed whale species can be grouped acoustically as either
producing broadband clicks or narrowband high-frequency (NBHF) clicks.
Recently, it has been shown that Heaviside’s dolphins, *Cephalorhynchus
heavisidii*, emit NBHF clicks for echolocation but also clicks of lower
frequency and broader bandwidth for communication. Here, we use acoustic
recorders and drone video footage to reinforce previous findings that
Commerson’s dolphins (*C. commersonii*) produce signals similar to
Heaviside’s dolphins. We reveal that they use clicks with a lower frequency
and broader bandwidth in the form of click trains and burst-pulses. These
sounds were not recorded in the presence of smaller groups of Commerson’s
dolphins, indicating that they may fulfil a communication function in
larger groups. Also, we utilised a novel combination of drone video footage
paired with underwater acoustic recordings to estimate the source level of
echolocation clicks produced by Commerson’s dolphins. In addition, we
compare the acoustic signals produced by Commerson’s and Heaviside’s
dolphins to identify interspecific similarities and differences. Spectral
differences were found in NBHF click trains, buzzes and burst-pulses
between species; however, bandwidth and duration parameters were not
significantly different for broadband click trains. Our findings make it
likely that all four species of the *Cephalorhynchus* genus have the
ability to generate both signal types, and further challenges the
evolutionary concept of NBHF signal production.

Significance statement:
This study confirms the presence of a dual echolocation click (i.e.
biosonar) strategy in Commerson’s dolphins, making them the second species
of their genus known to produce two types of biosonar. We provide an
in-depth quantitative analysis of Commerson’s dolphin acoustic signal
types, and include a comparison of signal types between Commerson’s
dolphins and the other species known to produce two types of biosonar, the
Heaviside’s dolphin. *In addition, this is the first study to combine drone
footage with underwater acoustic recordings to measure the source level of
toothed whale echolocation signals.* We use this novel technique to provide
source levels measured from Commerson’s dolphin echolocation clicks which
are comparable to published values for this species calculated using an
expensive and complicated array of hydrophones. Thus, we provide a simpler
and more cost effective way to study sounds produced by marine mammals.

This paper can be downloaded from: https://rdcu.be/cmXkC
Please feel free to email me for a pdf copy at mjmartin at sandiego.edu

Best wishes,
Morgan J. Martin, PhD

Postdoctoral researcher
University of Victoria, BC, Canada
Wildlife Conservation Society Canada
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