Toothed whales, such as dolphins, killer whales and sperm whales, have a diverse repertoire of sounds: They can use echolocation to locate their prey at depths of up to two kilometers, and their songs form complex vocalizations for social communication. How the giants of the oceans produce these sounds, however, was previously unclear. A study now shows that they have a special structure in their nose that works in a similar way to how the larynx works in humans. This nasal sound apparatus enables them to produce sounds in three different voice registers with minimal use of air.
When we humans speak or sing, we allow air to pass through the glottis in our larynx, causing the vocal cords to vibrate. With the vocal muscles we can regulate the tension of the vocal cords. This allows us to create different pitches and move through different so-called vocal registers, from the deep, raspy “vocal fry” to the normal chest voice we commonly use to speak and sing, to the high-pitched falsetto voice. Apart from humans, such vocal registers have so far only been detected in crows, which produce a similar effect with the vocal organ of birds, called the syrinx. This works on the same principle as our larynx.
Sound production in the nose
A new study now shows that toothed whales also have different vocal registers – thanks to a vocal organ in their nose. “It was previously unclear how whales are able to produce both echolocation calls and a rich vocal repertoire for social communication at depths of more than a kilometer under the sea surface,” writes a team led by Peter Madsen from Aarhus University in Denmark. Because whales face a special challenge: their lungs collapse as a reaction to the high pressure from a depth of 100 meters. In addition, when they dive into the deep sea, only a small amount of air remains in the nasal tract. How can an air-powered tuning system work under these conditions?
In order to gain detailed insights into the vocal system of toothed whales, Madsen and his team observed how trained dolphins and porpoises produce the so-called clicks for echolocation. To do this, the researchers used an endoscope to record high-speed videos inside the animals’ nasal tract and evaluated them in combination with sound recordings. The result: The echolocation clicks clearly originate in the nasal tract, not in the larynx of the toothed whale. In addition, the team was able to use the nasal vocal organ of a dead porpoise to produce the same sounds using air alone. “This refutes the previous hypothesis that whales use muscle power instead of airflow to produce the sounds,” the team said.
Saving air in the “Vocal Fry” register
Other measurements, both in trained toothed whales and in free-living toothed whales, have shown that the sound system of whales works on the same principle as the larynx in land mammals and the syrinx in birds – only the position is different. “Evolution has moved it from the trachea to the nose, which allows for a much higher propulsion pressure without damaging the lung tissue,” explains Madsen. “This high drive pressure enables the toothed whales to produce the loudest sounds of all animals on earth.” And that in three different registers: Just like us humans, the toothed whales can use both “vocal fry” and vocal registers, which our chest and falsetto voice.
The vocal register that whales use for echolocation is functionally equivalent to the human “vocal fry”. “Vocal Fry is a vocal range commonly used in American English, including by prominent figures such as Kim Kardashian, Kate Perry and Scarlet Johannsen,” explains co-author Coens Elemans from the University of Southern Denmark in Odense. While the vocal fry voice in humans is often felt to be rather creaky and uncomfortable, it has a decisive advantage for whales: “During the vocal fry, the vocal folds are only open for a very short time, so that very little breathing air is required will,” said Elemans. In this way, the whales can produce their high-frequency clicking sounds with less than 50 microliters of air per click. “Such air thrift enabled them evolutionarily to develop rich food niches in the deep sea, where they could hunt using echolocation,” the research team said.
Source: Peter Madsen (Aarhus University, Denmark) et al., Science, doi: 10.1126/science.adc9570