Toothed whales, like dolphins, orcas and sperm whales, communicate and capture food exclusively with sounds. A team of Danish researchers discovered that these animals have developed a new sound source in the nose, which has the same function as the human larynx.
Dolphins and other toothed whales are large predatory animals that often fascinate with their character and physiology: they are extremely sociable, cooperative and, in addition, can hunt prey up to two kilometers deep and in total darkness thanks to echolocation.
These extraordinary behaviors are due to sound, which travels at great speed and distance in dark, murky water. However, it is still a mystery how these animals make different sounds in the depths of the ocean.
Toothed whales have developed a nasal structure for new sounds
In light of this issue, a to study published by the magazine Science notes that toothed whales have developed an internal nasal structure that, powered by air, works in different registers, like the human voice.
The study was led by Coen Elemans, a scientist at the Department of Biology at the University of Southern Denmark, and Peter Madsen, a whale biologist at the Department of Biology at the University of Aarhus (Denmark).
This work shows that toothed whales, like humans, have at least three voice registers: the vocal fry or ‘vocal fluctuation’ (also known as squeaky voice, which produces the lowest tones), the chest register (the same as our normal voice) and the falsetto register (which produces the highest frequencies).
According to research, these cetaceans use the aforementioned ‘vocal flapping’ to emit their echolocation calls (through the reflection of sound waves) and hunt prey. “During ‘vocal flutter,’ the vocal cords are open for a very short time, so very little air is needed to use this register,” explains Elemans.
In turn, Madsen points out that “this air economy makes it ideal for echolocation” is that, what is more, “During deep dives, all the air is compressed to a small fraction of the volume at the surface.”.
Toothed whales dive to great depths
Toothed whales dive up to 2,000 meters deep and catch more fish than the human fishing industry. When hunting in deep, murky water, they emit short, powerful ultrasonic echolocation signals at speeds up to 700 (khz) per second to locate, track and capture their prey.
“Thus, the emission of bass sounds allows these odontocetes to access the richest food niches on the planet: the oceanic depths.”, in the words of Madsen.
“While this type of vocal range might be controversial in humans and perceived as annoying or even overbearing, it certainly meant evolutionary success for toothed whales.”, adds the scientist who led the study.
It used to be believed that toothed whales make sounds with their larynx, just like other mammals, but 40 years ago it became clear that this is not so; somehow they use their nose to produce sounds. In this study, the Danish research team used high-speed video through endoscopes to find out exactly how these animals are able to make these sounds.
The analysis concluded that toothed whales have developed an air-driven sound production system in their noses that functions physically analogously to laryngeal and syringal sound production in mammals and birds, although their location is far from the same. .
“Evolution has moved it from the trachea to the nose, allowing for much higher respiratory conduction pressures – up to five times what a trumpeter can generate – without damaging lung tissues.”, explains the co-author.
Furthermore, as the researchers point out, this high pressure allows toothed whales to emit “the loudest sounds of all animals on the planet”.
Phonic lips that vibrate like vocal chords
At depths greater than 100 meters, the lungs of whales collapse to prevent compression sickness. These organs are not used to supply air, so the rest is concentrated in the nasal passages of the skull. This provides a small but sufficient air gap to produce echolocation sounds at depths of up to 2000 meters below the surface.
When echolocating, toothed whales pressurize air from their noses and let it pass through structures called phonic lips, which vibrate like human vocal cords. Its acceleration produces sound waves that travel through the skull to the front of the head.
In addition to echolocation, toothed whales emit a huge variety of sounds for their complex social communication. “Some species, such as orcas and pilot whales, make very complex sounds that are learned and culturally transmitted like human dialects.”, emphasizes Madsen.
Finally, these scientists demonstrate in their study that these sounds are emitted by the phonic lips that vibrate in the chest and falsetto registers. They recorded these parts with several different methods, using trained dolphins and wild animals that moved with a small plate that recorded their sounds. Live recordings were made at Harderwijk Dolphinarium (Netherlands).
Reference:
Peter T. Madsen, Coen PH Elemans et. al: “Toothed whales use distinct vocal registers for echolocation and communication” Science (2023)