Animals
Scientists have discovered new insights into baleen whales’ anatomy that may also make them vulnerable to human noise pollution.
ByMelissa Hobson
Published February 21, 2024
Scientists have long wondered how baleen whales can sing while holding their breath. That’s because a whale’s larynx both makes sound and closes off their airway so they don’t drown. Try closing your mouth, holding your nose, and trying to hum—it won’t work.
“If you can’t let the air flow, the system is pressurized. When it’s pressurized, and flow stops, sound stops,” says Joy Reidenberg, a professor at Icahn School of Medicine at Mount Sinai in New York City who studies whale anatomy.
Experts already knew that whales have a special larynx with a bagpipe-like sac that enables them to sing, but they didn’t know exactly how they produced sound.
“You can’t just take an endoscope down a baleen whale and see what they’re doing when they’re singing,” says Reidenberg, who was not involved with the new study, published today in Nature. What’s more, dead whales usually decompose too quickly to collect viable tissue samples.
But three strandings close to his lab enabled lead author Coen Elemans, professor of bioacoustics at the University of Southern Denmark, to collect fresh vocal tracts from a recently deceased humpback, minke, and sei whale. (Learn why whales beach themselves.)
For the first time, Elemans could use these three larynxes to replicate what happens when the animals produce sound. That led to a surprising discovery: The animals’ vocal cords vibrate in an unexpected way to produce noise.
Party balloons—for science
Each of the three species create very different noises: humpbacks sing complex songs, minkes quack like ducks, and sei whales create low frequency booms. But how?
After conducting CT scans, the team situated the three larynxes in a laboratory air space and slowly blew air through the system to see if they could mimic a whale’s gigantic lungs.
“We ended up using party balloons to power the setup,” Elemans says.
They’d assumed that the inner edges of the whales’ vocal cords rub together to make sound, but the experiment revealed the vocal cords instead rub together against a fat pad at the back of the larynx.
“No other animal does vocalizations in that way,” says Reidenberg.
Reidenberg wonders if the two vocal cords can vibrate at different frequencies against the fat cushion, or whether they can also vibrate against each other. This could explain how a whale can make more than one sound at once.
Elemans thinks these adaptations arose when whales’ land ancestors returned to the ocean around 50 million years ago. Because baleen whales needed to communicate with other whales while using their larynx for food and airway separation, they evolved this unique system.
“These animals physiologically made up a totally new evolutionary novelty to make sound underwater with this weird larynx,” he says.
More investigation needed
Reidenberg cautions the sample size of the study—just three animals—is too small for such a generalization, and that scientists need to examine more specimens first.
Heidi Pearson, professor of marine biology at University of Alaska Southeast, who was also not involved in the study, agrees. She’d like to see a different family of whales examined for comparison, as the three individuals studied were all juvenile rorqual whales. Elemans says he wants to study an adult male, which are known for their singing.
But the experts acknowledge the inherent challenge in doing so. “Just getting those samples is a triumph in its own right,” says Pearson. (Read about a mysterious new humpback whale song detected.)
Controlling noise pollution
The researchers also used 3-D computer simulations to mimic what happens when the whales’ larynx muscles are activated. They discovered these structures cannot produce sound at higher frequencies than 300 hertz (Hz), or below depths of about 330 feet.
Unfortunately, that “depth and frequency range overlap almost perfectly with what humans make,” says Elemans, meaning they may struggle to compete with noise generated by shipping vessels, which emit sounds between 30 and 300 Hz.
“It’s what you and I might call a cocktail party effect,” says Reidenberg. When your vocal range overlaps with everyone else’s, it becomes harder to hear each other without raising your voice.
That’s why the study highlights an urgent need to decrease noise pollution by limiting vessel traffic, implementing slow zones, protecting areas with lots of vocalizing whales, and making ships quieter, says Pearson, and using real-time data in conservation plans. (Read: “We might lose these whales for good if we don’t slow down.”)
Reidenberg has a good example of how to do that: If an offshore wind farm in New York conducted a seismic survey during winter, it wouldn’t interfere with whale vocalizations, she says, because “the singers are all down having spring break in the tropics.”
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