Walruses produce intense impulse sounds by clap-induced cavitation during breeding displays.

Ole Næsbye Larsen,Colleen Reichmuth

doi:10.1098/rsos.210197

Ole Næsbye Larsen, Colleen Reichmuth

Open Access

https://doi.org/10.1098/rsos.210197

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Abstract

Male walruses produce some of the longest continuous reproductive displays known among mammals to convey their physical fitness to potential rivals and possibly to potential mates. Here, we document the ability of a captive walrus to produce intense, rhythmic sounds through a non-vocal pathway involving deliberate, regular collision of the fore flippers. High-speed videography linked to an acoustic onset marker revealed sound production through cavitation, with the acoustic impulse generated by each forceful clap exceeding a peak-to-peak sound level of 200 dB re. 1 µPa. This clapping display is in some ways quite similar to the knocking display more commonly associated with walruses in rut but is produced through a very different mechanism and with much higher amplitudes. While this clapping behaviour has not yet been documented in wild individuals, it has been observed among other mature male walruses living in human care. Production of intense sounds through cavitation has previously been documented only in crustaceans but may also be an effective means of sound production for some aquatic mammals.

Highlights

Soundscapes of the oceans are dominated by water motion, weather and distant ship noise and are influenced by rarer events like lightning, underwater earthquakes, discrete anthropogenic noise sources and the breaking and cracking of sea ice [1,2,3]
Sivuqaq clapped only during the mating season each year from February to May and always under water. His rhythmic clapping behaviour was often associated with sexual arousal and the production of other underwater sounds, including intense knock sounds delivered at a similar rate
Associated complete audio and video datasets are available in Dryad [23]. These powerful impulse sounds can be explained by the mechanism of clap-induced cavitation

Summary

Introduction

Soundscapes of the oceans are dominated by water motion, weather and distant ship noise and are influenced by rarer events like lightning, underwater earthquakes, discrete anthropogenic noise sources and the breaking and cracking of sea ice [1,2,3]. Biological sounds produced by crustaceans, fishes and marine mammals punctuate the soundscapes, which vary considerably with location and time [4]. This means that ambient underwater sound levels can be high over a wide royalsocietypublishing.org/journal/rsos R. Aquatic animals that communicate using sound must produce signals that are 2 sufficiently powerful to relay their message to intended receivers Aside from social contexts, high-amplitude underwater sounds can be generated during foraging activity or interaction with predators Aside from social contexts, high-amplitude underwater sounds can be generated during foraging activity or interaction with predators (e.g. [5])

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