These whales still use their vocal cords. But how?

People have been telling stories about strange underwater sounds for thousands of years, but it wasn't until the mid-20th century that scientists were able to pinpoint one of the causes: whales, singing, whistling and squealing in the blue.

The way some whales make these sounds has remained a mystery. a study published Wednesday in the journal Nature puts forward a new explanation, discovered thanks to a device that forced air through the vocal cords of three dead whales.

The larynx, or larynx, is an ancient organ. “It arose when fish crawled out of the sea and animals needed a way to separate the air they breathe from the food they ingest,” says Coen Elemans, author of the study and professor of biology at the university. of southern Denmark.

The larynx functions as an antechamber to the trachea, or trachea, with a flap of tissue called the epiglottis that keeps food and drink from falling through the trachea. Slightly below the epiglottis, mammals have developed additional folds of tissue called vocal cords or vocal folds, which produce sounds when air exhaled from the lungs causes them to vibrate.

When the land-dwelling ancestors of whales returned to life in the sea, “they actually had to change the larynx, because when these animals breathe on the surface, they have to expel a lot of air very quickly,” said Dr. Elemans. Vocal folds like those of land mammals can get in the way.

Toothed whales, like sperm whales and dolphins, use their larynx like a cork to close off their airways; they developed a way to produce sounds in their nasal passages instead. But scientists suspected that filter-feeding baleen whales, including the musical humpback whales and the enormous blue whales, still use their voice boxes.

These whales are too large to keep in captivity and tend to perform most of their vocalizations too deep underwater for divers to collect ultrasound or MRI data. Instead, Dr. Elemans and his colleagues came up with the next best thing: freshly preserved voice boxes dissected from three baleen whales that had died after being stranded on land, two in Denmark and one in Scotland. One was a humpback whale, one a minke whale, the last a sei.

The researchers attached the whales' two-meter-long voice boxes to a series of pipes and pumped air through them. Initially the voice boxes did not make any sound. But when the researchers moved the larynx so that a fat pad attached to it vibrated against the vocal folds, the laboratory was filled with the sounds of a vocalizing whale.

In terms of excitement among the researchers in the lab, “on a scale of one to 10 it was an 11,” says W. Tecumseh Fitch, author of the study and professor of cognitive biology at the University of Vienna. This way of producing sound, which involves squeezing air between a fat pad and the vocal folds, has never been seen in any other animal.

Joy S. Reidenberg, professor of anatomy at the Icahn School of Medicine at Mount Sinai, who was not involved in the study, said the experiment “changes our perspective on how sounds are made in these whales, and it may show us a mechanism see how the whales can make more than one sound at the same time.”

She noted that the study was limited by the small number of whale voice boxes available for analysis, and that it could be fruitful to examine a larger number of specimens, especially adult male humpback whales that produce complex songs.

The researchers also created digital models to investigate how limitations on lung capacity and water pressure could affect where and how the whales cast their votes. The findings suggested that whales are limited to uttering sounds in shallower water. Unfortunately, this is also where noise from human activities such as shipping can disrupt whale vocalizations.

Christopher W. Clark, professor emeritus of neurobiology and behavior at Cornell University, who was not involved in the project, said the complexity of sound traveling underwater suggests that whales' ability to communicate may not be as hampered by ship noise as the new sound. study suggests.

And, he said, the study provides a “road sign” showing where researchers should focus to learn how and where whales actually communicate with each other.