It has always been a mystery as to how dolphins, porpoises, killer whales, sperm whales and other toothed whales produce an array of sounds – until now.
Researchers have found that it’s all in the nose.
The animals create loud clicking sounds for echolocation – the process of locating prey through sound waves – and also softer burst pulses and whistles for communication.
Scientists say that sound is created by an air-driven system in the nose, similar to the voice box in humans.
The study, which was published in the journal of Science, also revealed that this air-powered blast of sound is a way for the toothed whales to locate food in the deep water.
The loudest sounds in the animal kingdom
Peter Madsen, a sensory physiology professor and expert in whale biology at Aarhus University in Denmark, said: “Echolocating toothed whales make the loudest sounds in the animal kingdom by forcing highly pressurised air past structures called phonic lips in their nose”.
Professor Madsen said the phonic lips open for about a millisecond and when they “slap back together they create a tissue vibration that forms a very loud click in the water in front of the whale that is used to echolocate prey down to more than 1,000 meters depth.”
The phonic lips consist of connective tissue and fat.
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The study revealed that the sounds produced operated at different vocal registers like the human voice.
Scientists said it was a fry register for clicks, a chest register for burst pulses and a falsetto register for whistles.
For humans the fry register represents the lowest tones, the chest register is the normal speaking voice and the falsetto register is at a higher frequency.
The sounds are said to be created “by the same mechanism, namely air flow-induced self-sustained oscillations”, said study co-leader Coen Elemans, a University of Southern Denmark bioacoustics professor.
“But the critical difference is that in humans and other land mammals, air is used both as the propellant that makes the vocal folds vibrate and as the medium in which the sounds are propagated,” he added.
Whales evolved an entirely new set of sound sources
The researchers used sound-recording tags on sperm whales, false killer whales and bottlenose dolphins to study sound production in the wild.
They used video from an endoscope – a thin, tube-like instrument – to image the phonic lips in harbour porpoises and bottlenose dolphins in captivity. They also looked at the phonic lip operation and anatomy in dead-stranded porpoises.
“During the course of evolution, toothed whales have lost their vocal folds, but evolved an entirely new set of sound sources in the nose,” Professor Madsen added.
