People have told stories about strange underwater sounds for thousands of years, but it wasn’t until the mid-20th century that scientists discovered one of the causes: whales, singing and whistling and screeching in the blue sea.
The way in which some whales produce this sound has remained a mystery. A study published Wednesday in the journal Nature provides a new explanation, discovered thanks to a device that forced air through the voice boxes of three dead whales.
The voice box, or larynx, is an ancient organ. “It developed when fish crawled out of the sea and the animals needed a way to separate the air they breathed from the food they swallowed,” said Coen Elemans, one of the authors of the study and a biology professor at the University of Southern Denmark.
The larynx functions like a waiting room for the throat, or trachea, with tissue called the epiglottis keeping food and drink from entering the trachea. Slightly below the epiglottis, mammals have developed additional folds of tissue, called vocal cords or vocal folds, that produce sound when air expelled from the lungs makes them vibrate.
When the land-dwelling ancestors of whales returned to the sea, “they basically had to change the larynx, because when these animals were surface-breathing, they needed to expel a lot of air quickly,” says Dr. Elements. Vocal folds like those of land mammals can get in the way.
Toothed whales, such as sperm whales and dolphins, use their larynx like a plug to seal their airways; they evolved a way of producing sound in their nasal cavity. But scientists suspect that baleen whales, including humpback whales and blue whales, still use their voice boxes.
These whales are too large to be kept in captivity and tend to do most of their talking in water that is too deep to allow divers to collect ultrasound or MRI data. Instead, Dr. Elemans and his colleagues examined the next best thing: freshly preserved voice boxes autopsied from three baleen whales that had died after strandings, two in Denmark and one in Scotland. One humpback, one minke, and one sei.
The researchers attached the whale’s two-foot voice box to a series of pipes and channeled air through them. At first, the ballot box failed to produce any sound. But when the researchers positioned the larynx so that the fat pads connected to the sound vibrated against the vocal folds, the lab was filled with the sound of a whale singing.
In terms of excitement among researchers in the lab, “on a scale from one to 10, it’s an 11,” said W. Tecumseh Fitch, an author of the study and a professor of cognitive biology at the University of Vienna. This way of producing sound, with air compressed between the fat pad and the vocal folds, has never been seen in other animals.
Joy S. Reidenberg, a professor of anatomy at the Icahn School of Medicine at Mount Sinai who was not involved in the research, said the experiment “changes our perspective on how sound is made in these whales, and may show us the mechanisms that might be used by whales to produce more than one sound at the same time.”
He noted that the study was limited by the small number of whale voice boxes available for analysis, and that it might be beneficial to examine a larger number of samples, especially male adult humpback whales that produce complex songs.
The researchers also created digital models to examine how lung capacity constraints and water pressure might affect where and how whales make their calls. These findings suggest that whales are limited to making sounds in shallow waters. Unfortunately, this is also a place where sounds from human activities such as shipping may interfere with whale sounds.
Christopher W. Clark, a professor emeritus of neurobiology and behavior at Cornell University who was not involved in the project, said that the complexity of sounds traveling underwater suggests that whales’ ability to communicate may not be as impaired by shipping noise as this study suggests. .
And, he said, the study offers “road signs” showing where researchers should focus to learn about how and where whales actually communicate with each other.
2024-02-21 18:06:25
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