[MARMAM] New publication on frequency decline of blue whale calls

Ally Rice ally.c.rice at gmail.com
Fri Apr 1 15:23:30 PDT 2022

Dear MARMAM community,

My coauthors and I are pleased to announce the publication of our paper,
"Update on frequency decline of Northeast Pacific blue whale (*Balaenoptera
musculus*) calls" in *PLOS ONE*.

Ally Rice, Ana Širović, John A. Hildebrand, Megan Wood, Alex
Carbaugh-Rutland, and Simone Baumann-Pickering

Worldwide, the frequency (pitch) of blue whale (*Balaenoptera musculus*)
calls has been decreasing since first recorded in the 1960s. This frequency
decline occurs over annual and inter-annual timescales and has recently
been documented in other baleen whale species, yet it remains unexplained.
In the Northeast Pacific, blue whales produce two calls, or units, that,
when regularly repeated, are referred to as song: A and B calls. In this
population, frequency decline has thus far only been examined in B calls.
In this work, passive acoustic data collected in the Southern California
Bight from 2006 to 2019 were examined to determine if A calls are also
declining in frequency and whether the call pulse rate was similarly
impacted. Additionally, frequency measurements were made for B calls to
determine whether the rate of frequency decline is the same as was
calculated when this phenomenon was first reported in 2009. We found that A
calls decreased at a rate of 0.32 Hz yr-1 during this period and that B
calls were still decreasing, albeit at a slower rate (0.27 Hz yr-1) than
reported previously. The A call pulse rate also declined over the course of
the study, at a rate of 0.006 pulses/s yr-1. With this updated information,
we consider the various theories that have been proposed to explain
frequency decline in blue whales. We conclude that no current theory
adequately accounts for all aspects of this phenomenon and consider the
role that individual perception of song frequency may play. To understand
the cause behind call frequency decline, future studies might want to
explore the function of these songs and the mechanism for their
synchronization. The ubiquitous nature of the frequency shift phenomenon
may indicate a consistent level of vocal plasticity and fine auditory
processing abilities across baleen whale species.

Available at:


Ally Rice
Staff Research Associate II
Scripps Acoustic Ecology Laboratory
Scripps Institution of Oceanography, UCSD
office: 858-534-5755
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