How whales sing underwater
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A humpback whale calf in the waters of Moorea. Photo: Karim Iliya
The songs of humpback, blue and other baleen whales are generated by the unusual anatomy of their larynx, according to a new paper.
Why it matters: A whale's song helps it find other animals in the vast ocean and plays a large role in their behavior, study co-author Coen Elemans, a professor at the University of Southern Denmark, told PopSci.
- "Thus understanding how they make sound is crucial to understand the biology of whales in general."
The big picture: Humans and other terrestrial mammals have vocal cords — paired folds of tissue in the larynx that vibrate when air exhaled from the lungs passes through the gaps between paired folds, producing sound.
- When the land mammals that were ancestors of today's whales returned to the sea, they needed to be able to inhale and exhale large volumes of air when they surfaced to breathe and to hold that air in when they sang underwater, the authors write in the journal Nature.
- Toothed whales — orcas and sperm whales, for example — use the larynx to seal the airway and have a vocal organ in their nose that makes sounds.
- Baleen whales, on the other hand, have an unusual larynx that serves both respiratory and sound-producing functions. But scientists didn't know how the organ generates sounds.
What they did: The team studied larynges removed from three baleen whales — a sei, a humpback and a minke — that had died from various suspected causes.
- Using an air supply system to mimic the whale lung, they pushed air through the extracted larynges and found sound was produced when air flowed through a space between a fatty pad and the top surface of the vocal folds, which vibrated.
What they found: It's a small number of samples, but the team concluded baleen whales evolved "unique laryngeal structures .... [that] allow some of the largest animals that ever lived to efficiently produce frequency-modulated, low-frequency calls," they write.
- But digital models built by the team indicate the structures also put "physiological limits" on the sounds the whales can make. They can only be produced in shallow waters — where there are also boats — and at lower frequency sounds that are similar to those made by vessels.
- That prevents them from escaping noise from ocean vessels and reduces their communication range, the authors write.
Yes, but: The complexities of sound traveling underwater suggested whales' ability to communicate might not be quite as hampered by shipping noise as the new study suggests, Christopher Clark, a professor emeritus of neurobiology and behavior at Cornell University told the NYT.
The bottom line: The study is "a game-changer for understanding how biological sounds are generated," Joy Reidenberg, a professor of anatomy at the Icahn School of Medicine at Mount Sinai wrote in an accompanying article.
