Dolphins and other toothed whales are social, highly intelligent predators, which can hunt prey down to two kilometers deep in complete darkness using echolocation. Although scientists have long known that these remarkable behaviors are mediated by sound that travels fast and far in murky, dark waters, until recently, the precise way in which this processes functions has remained a mystery.
Now, a team of scientists led by the University of Southern Denmark (SDU) and Aarhus University has found that toothed whales evolved an air-driven nasal sound source which, just like the human voice, operates at different registers, allowing them to locate their prey in deep waters. These registers include the vocal fry register (which produces the lowest tones), the chest register (which is similar to humans’ normal speaking voice), and the falsetto register (which produces high frequencies). The researchers found that toothed whales use the vocal fry register to produce echolocation calls that help them catch prey.
“Vocal fry is a normal voice register that is often used in American English. Kim Kardashian, Kate Perry, and Scarlet Johannsen are well-known people using this register,” said study senior author Coen Elemans, an expert in Sound Communication and Behavior at SDU. “During vocal fry, the vocal folds are only open for a very short time, and therefore it takes very little breathing air to use this register.”
Although it was previously thought that toothed whales make sounds with their larynx just like other mammals, four decades ago scientists discovered that, in fact, they use their noses to produce sound. In the current study, the experts found that these animals evolved an air-driven sound production system in their nose which, although it functions in a physically analogous way to laryngeal and syringeal sound production in mammals and birds, is not located in the same place.
“Evolution has moved it from the trachea into the nose, which allowed much higher driving pressures – up to five times what a trumpet player can generate – without damaging lung tissues,” explained study lead author Peter Madsen, a biologist at Aarhus.
“This high driving pressure allows toothed whales to make the loudest sounds of any animal on the planet,” Elemans added.
At depths over 100 meters, the whales’ lungs collapse in order to avoid compression sickness, while the remaining air – found in the nasal passages – provides a small, but sufficient airspace to produce echolocating sounds at depths of up to 2,000 meters. When echolocating, the whales pressurize air in their bony nose and let it pass through structures called phonic lips which vibrate in a similar way to human vocal folds.
“While vocal fry may be controversial in humans and may be perceived as everything from annoying to authoritative, it doubtlessly made toothed whales an evolutionary success story,” Elemans concluded.
The study is published in the journal Science.
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