The secret of whale song hidden deep in their larynx

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The humpback whale is a baleen whale.

Agency France-Presse

Mysticetes, also called baleen cetaceans, sing thanks to a unique system in their larynx operating on a principle similar to that of terrestrial mammals such as humans, and described for the first time in a study published in the journal Nature (New window) (in English).

By returning to the sea around 50 million years ago, the ancestors of whales had to adapt their communication system to avoid drowning. Odontocetes, toothed cetaceans like the current dolphin, developed a nasal organ allowing them to emit sounds.

Scientists thought that for their part mysticetes, like the blue whale or the rorqual, used their larynx to produce vocalizations. But the mechanism of their anatomy allowing these songs was not really understood, recalls an article accompanying the study.

The first sailors had detected these strange sounds, initially attributed to mythical creatures or to the imagination of drunken sailors, recalls American anatomist Joy Reidenberg in the article.

It was only with access, after the Second World War, to the sounds recorded by military hydrophones that researchers understood that these songs were produced by whales.

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The 420,000 members of the Common Front accept the agreement in principle at 74.8% =”StyledBodyHtmlParagraph-sc-48221190-4 hnvfyV”>In the study, the international team led by Coen Elemans, from the Department of Biology at the University of Southern Denmark in Odense, combined experiments on larynxes of three mysticete species (humpback whale; minke whale; sei whale) with anatomical and computer models.

She concluded that these animals had evolved unique laryngeal structures for the production of sounds.

Once his lungs are full of air, after an inspiration with his vent and the closing of valves preventing the intrusion of water, the whale produces its song by pushing air through its larynx.

It vibrates between cartilaginous cords, much like air does between the vocal cords of a human to produce a sound. Before passing into a pocket, called the laryngeal, which allows its recycling towards the lung before a new vocalization.

Coen Elemans' discovery is the alternative, and perhaps concomitant, depending on the species, use of a fat pad located above the cartilaginous cords. It would produce another sound.

This observation was obtained by recording the vibrations produced by an air flow in the larynx samples . Which still remains impossible to observe on a living animal, given its size, notes Joy Reidenberg.

She nonetheless wonders whether the hypothesis arising from the study could explain how certain whales manage to produce at least two different sounds at the same time.

One ​​of the limitations of the experiment is its holding in the open air with larynx samples. Which does not explain how sounds produced inside the animal can propagate outside in the water, with all hatches closed.

The measurements carried out by Coen Elemans' team also set physiological limits to the frequency ranges of songs, their duration and the depth up to 100%. at which whales can emit them.

These vocalizations would thus be located essentially at the same depths and frequencies as the sounds produced by maritime traffic. Disrupting possible communication between cetaceans.