A study published Wednesday February 21 provides a breakthrough on the fascinating vocalization of whales. The anatomical mechanism of this song, which has intrigued scientists for a long time, had never been identified.
According to the revelations of the study published in Nature and led by Coen Elemans, from the biology department of the University of Southern Denmark in Odense, mysticetes, also called true whales, sing thanks to a unique system in their larynx, functioning on a principle similar to that of terrestrial mammals such as human beings.
Scientists assumed that mysticetes – baleen cetaceans like blue whales or rorquals – used their larynx to produce vocalizations. But the mechanism of their anatomy allowing these songs was not really understood, recalls the Nature article.
Also read: Fall asleep while listening live to the song of whales in the Pacific Ocean
To carry out their study, the international team combined experiments on the larynxes of three species of mysticetes (humpback whale, Minke whale and sei whale) with anatomical and computer models. According to his findings, these animals had developed "unique laryngeal structures for sound production."
Two sounds at the same time
Once its lungs are full of air, after inhaling with its blowhole and closing 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 a human's vocal cords 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 make it possible to 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 American anatomist Joy Reidenberg.
She nonetheless wonders if the hypothesis arising from the study could explain how certain whales manage to produce at least two different sounds at the same time.
Communication disrupted by maritime traffic
One of the limitations of the experiment is its holding in the open air with larynx samples. This 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 to which whales can emit them.
Also read: Why whales have grown enormously in size in a few million years
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.
These strange sounds have fascinated travelers for a long time. The first sailors attributed them to mythical creatures or to "the imagination of drunken sailors", recalls Joy Reidenberg in the article.
It was only with access, after World War II, to sounds recorded by military hydrophones that researchers understood that these songs were produced by whales.
With AFP
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