Dear marmam,
It is our pleasure to share our recent publication on the biosonar and
movement strategy of Sowerby's beaked whales.
The first biologging data on this species, from individuals tagged off
Terceira, Azores with Dtags, showed surprisingly fast swimming and
hunting behaviour, combined with fast, high frequency echolocation.
These findings suggest a much wider range of deep-sea foraging niches
and strategies in beaked whales than currently expected, as well as a
possibly different beaked whale response strategy to anthropogenic
sounds.
Link to the open access paper:
https://journals.biologists.com/jeb/article/225/9/jeb243728/275372/Sowerby-s-beaked-whale-biosonar-and-movement
Authors: Fleur Visser, Machiel G Oudejans, Onno A Keller, Peter T Madsen
and Mark Johnson.
Abstract:
Closely-related species are expected to diverge in foraging strategy,
reflecting the evolutionary drive to optimize foraging performance. The
most speciose cetacean genus, the mesoplodonts, are beaked whales with
little diversity in external morphology or diet, and overlapping
distributions. Moreover, the few studied species of beaked whales
(Ziphiidae) show closely-similar foraging styles with slow,
energy-conserving movement during long, deep foraging dives. This raises
the question of what factors drive their speciation. Using data from
animal-attached tags and aerial imagery, we test the hypothesis that two
similar-sized mesoplodonts, Sowerby's (Mesoplodon bidens) and
Blainville's (M. densirostris) beaked whales, exploit a similar
low-energy niche. We show that, compared to the low-energy strategist
Blainville's beaked whale, Sowerby's beaked whale lives in the fast
lane. While targeting a similar meso/bathypelagic foraging zone, they
consistently swim and hunt faster, perform shorter deep dives,
echolocate at a faster rate and with higher frequency clicks. Further,
extensive near-surface travel between deep dives challenges the
interpretation of beaked whale shallow inter-foraging dives as
management of decompression sickness. The distinctively higher frequency
echolocation clicks do not hold apparent foraging benefits. Instead, we
argue that a high-speed foraging style influences dive duration and
echolocation behaviour, enabling access to a distinct prey population.
Our results demonstrate that beaked whales exploit a broader diversity
of deep-sea foraging and energetic niches than hitherto suspected. The
marked deviation of Sowerby’s beaked whales from the typical Ziphiid
foraging strategy has potential implications for their response to
anthropogenic sounds, which appear to be strongly behaviourally-driven
in other Ziphiids.
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