After a decade of work, a Danish-German research team deciphered how toothed whales generate the clicks they use to locate and catch their fast-swimming prey in the dark depths. The study shows that over the course of evolution, orcas, dolphins, narwhals and others developed a structure in their nose through which they press air, producing the clicking sounds.
Toothed whales, which also include belugas and narwhals native to the Arctic, as well as orcas, some beaked whales and dolphins present in Arctic and Antarctic waters, usually find their prey in water depths where little or no light penetrates. Therefore, they must rely on their echolocation for hunting. The clicks that whales emit to locate their prey is almost like the focused beam of a flashlight. That’s how voice scientist Coen Elemans, a professor at the University of Southern Denmark and leader of the study, describes it to NPR.
Until now, however, it was not clear how the whales produce these clicks at depths of several hundred or even thousand meters under high water pressure. With perseverance and specially developed technology, the team has managed to unravel this long-kept secret. They were helped by trained dolphins in the Dutch dolphinarium Harderwijk and also free-living porpoises. Their findings very likely apply to all toothed whales.
The team was able to show that toothed whales evolved an air-driven sound source in the nose – the phonic lips – that is physically analogous to sound production in the larynx in mammals and the syrinx in birds.
Thanks to their phonic lips, whales can make full use of their vocal repertoire even at great water depths, which – as with us humans – consists of at least three vocal registers: 1. The vocal fry register, which produces the lowest notes; 2. the chest register, which is the normal speaking voice in humans; and 3. the falsetto, the highest frequency of the voice.
According to the study results, toothed whales use the lowest vocal pitch, the pulse register (aka vocal fry register), to generate echolocation clicks. The team found this out only with the help of high-speed videos taken with endoscopes. “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,” Elemans describes.
“And this air-economy makes it especially ideal for echolocation,” Professor Peter Madsen says, a cetacean biologist at Aarhus University in Denmark and lead author of the study. “During deep dives, all air is compressed to a tiny fraction of the volume on the surface.” Madsen adds that sound production using vocal fry gives whales access to the richest food niches on Earth: the deep sea.
“Evolution has moved it from the trachea into the nose, which allowed much higher driving pressures – up to 5 times what a trumpet player can generate – without damaging lung tissues,” explains Madsen. “This high driving pressure allows toothed whales to make the loudest sounds of any animal on the planet,” Elemans adds.
If the whales dive deeper than 100 meters their lungs collapse to avoid pressure sickness. They are then no longer available for air supply. This creates a small airspace sufficient to generate echolocation clicks even at great depths of up to 2000 meters.
In echolocation, whales increase the pressure in their bony noses, allowing air to flow past phonic lips that vibrate much like human vocal folds. This acceleration generates sound waves that propagate through the skull to the front of the head.
Sounds used by cetaceans to communicate are also produced by the phonic lips, which then vibrate in the chest or falsetto register. This especially helps with communication within groups and is evidence of a high degree of socialization in many toothed whale species.
Julia Hager, PolarJournal
More on the subject:
