People have told stories of strange underwater sounds for thousands of years, but it took until the mid-20th century for scientists to pinpoint one of the causes: whales, singing and whistling and screeching in the blue.
The means by which some whales make these sounds has remained a mystery. A study published Wednesday in the journal Nature offers a new explanation, discovered thanks to a machine that forced air through the voice boxes of three dead whales.
The voice box, or larynx, is an ancient instrument. “It evolved when fish were dragged out of the sea and the animals needed a way to separate the air they breathed from the food they ingested,” said Coen Elemans, study author and professor of biology at the University. of Southern Denmark.
The larynx acts as a vestibule to the windpipe, with a flap of tissue called the epiglottis that prevents food and drink from falling into the windpipe. Just below the epiglottis, mammals have developed additional folds of tissue, called the vocal cords or vocal cords, which produce sounds when air exhaled from their lungs causes them to vibrate.
When the land-based ancestors of whales returned to life in the sea, “they basically had to change the larynx, because when these animals breathe at the surface, they have to expel a lot of air very quickly,” Dr. Ellemans said. Vocal folds like those of land mammals could get in the way.
Toothed whales, like whales and dolphins, use their larynxes like corks to seal their airways. they evolved a way to produce sounds in their nasal cavities. But scientists suspected that filter-feeding baleen whales, including musical humpbacks and giant blue whales, still use their voice boxes.
These whales are too large to keep in captivity and tend to make most of their calls too deep underwater for divers to collect ultrasound or MRI data. Instead, Dr. Ellemans and his colleagues looked at the next best thing: freshly preserved voice boxes cut from three whales that had died after stranding, two in Denmark and one in Scotland. One was a hunchback, another a mink, the last a shei.
The researchers attached the whales’ two-foot-long voice boxes to a series of tubes and pumped air through them. At first, the voice boxes failed to make any noise. But when the researchers repositioned the larynx so that a fat pad attached to it vibrated the vocal cords, the lab was filled with the sounds of a whale calling.
As for the excitement among the researchers in the lab, “on a scale of one to 10, it was an 11,” said W. Tecumseh Fitch, a study author and professor of cognitive biology at the University of Vienna. This means of sound production, with air compressed between a pad of fat and the vocal folds, has never been seen in another animal.
Joy S. Reidenberg, a 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 produced in these whales and may show us a mechanism by which whales could use to make more than one sound at once.”
He noted that the study was limited by the small number of whale vocalizations available for analysis, and that it might be fruitful to examine a larger number of samples, especially adult male humpbacks that produce complex songs.
The researchers also created digital models to examine how limitations in lung capacity and water pressure might affect where and how the whales call. The findings suggest that the whales are restricted to calling in shallower waters. Unfortunately, this is also where noise from human activities such as shipping can interfere with whale calls.
Christopher W. Clark, an emeritus professor of neurobiology and behavior at Cornell University who was not involved in the project, said the complexity of sound that travels underwater suggests that the whales’ ability to communicate may not be as hindered by shipping noise as the new the study suggests.
And, he said, the study offers a “road sign” that shows where researchers should focus to learn how and where whales actually communicate with each other.
