Dolphins can use vocal fry like Katy Perry to hunt their prey

In the Rock and Roll Hall of Fame should appear new singers along with masters of falsetto Freddie Mercury, Prince and Mika: dolphins and all other odontocetes. According to a recent study, these animals can not only use falsetto, i.e. emit sounds with higher frequencies than their normal vocalizations, but they also have other two vocal registersa “chest voice”, which they most commonly use, and a lower one called “laryngealization“, in English “vocal fry“, used for capture their prey.

Modulating the voice in this way for animals with such a developed sociability and with such a refined acoustic communication system is essential. Let’s imagine for a moment dive off into the Mediterranean with special microphones: under the glitter of the water reflecting a hot summer sun, a pod of common dolphins is hunting a school of fish. They try to get around them, they call each other by name, they look for each other tens of meters away and they do it with a complex vocabulary made of crunches, tongue clicks and much more.

All of these behaviors are mediated by sounds that travel rapidly very far and to this day it is still a mystery how the complex vocabulary of these incredible marine mammals is made up. Now, however, a new study by a team of scientists from the University of Southern Denmark and Aarhus University published in the journal Science delves into the matter: dolphins and other odontocetes have developed a nasal sound source with different vocal registers including the vocal fry, which is used during hunting.

3D image showing the internal structures of a porpoise.  The two parts of the body that produce the vocal fry are highlighted, including the melon, in yellow, which disperses the sound in the water.  Image by Christian B. Christensen, Madsen et al., 2023
in the picture: 3D image showing the internal structures of a porpoise. The two parts of the body that produce the vocal fry are highlighted, including the melon, in yellow, which disperses the sound in the water. Image by Christian B. Christensen, Madsen et al., 2023

“There laryngealization it is a normal vocal register that is also used very often among humans. Famous people who use it include Kim Kardashian, Katy Perry and Scarlet Johannsen,” explains Coen Elemans, professor at the University of Southern Denmark and co-author of the study.

This is the lowest human vocal register known and is produced through a relaxation of the closure of the epiglottis, the cartilage that separates the airways from the digestive tract, allowing air to “crackleslowly with a clicking or crackling sound at a very low frequency. During this phonation, the cartilages in the larynx are drawn together, causing the vocal cords to compress quite tightly and become relatively soft and firm.

This process forms a large, irregularly vibrating mass within the vocal cords that produces the characteristic sound. There is even someone who holds the world record for the lowest frequency note ever produced by a human with this register: Tim Storms who managed to produce a sol -7 at a frequency of only 0.189 Hzinaudible to the human ear.

A great example of vocal fry it can be heard in an episode of the English version of the TV series Loudermilk. In the clip, the protagonist orders a drink in a cafeteria and is served by a young saleswoman who uses just that vocal timbre. The scene is not intended to explain its usefulness for humans, but simply shows how sometimes many of us use it without realizing it, sometimes with unnerving effects for other people.

According to the researchers, the odontocetes, a suborder of cetaceans which includes dolphins, sperm whales and killer whales, use this vocal register to produce echolocation aimed at catching prey. «During the vocal fry the vocal cords are only open for a very short time and therefore it takes very little air to use this register – adds Elemans – This makes it an ideal tool for echolocation since, during deep dives, all the air is compressed in a small fraction of its volume.

In fact, many odontocetes they also dive to 2,000 meters of depth and when they hunt in such deep and turbid waters they produce short and powerful ultrasounds, a series of “clicks” which can reach up to 700 per second, useful for identifying, tracking and capturing prey, just as the scientist explains: «Thus the vocal fry allows access to a part of the sea which is among the richest in food: the deep ocean».

To find out the Danish researchers have used high speed video and endoscopes to visualize the internal parts of some animals, investigating which are the structures that produce the peculiar register. Scholars have thus discovered that the odontocetes have developed a sound production system by passing air through their nosea system analogous to the sound made via the larynx and syrinx in mammals and birds.

“Evolution moved breathing in these animals from the trachea to the nose, which allowed them to generate leak pressures of the air very strong, up to 5 times stronger than a trumpet player pushing air into his instrument – ​​continues Coen Elemans – This high pressure allows odontocetes to emit the loudest sounds of any animal on the planet».

Unlike the reed of a trumpet, however, odontocetes in echolocation pressurize the air in their nose and pass it through structures called “phonic lips”, which vibrate just like human vocal cords. Their acceleration produces sound waves that travel through the skull up to the front of the head.

In short, we never expected to be able to compare Katy Perry’s vocal timbre with that of a dolphin, but scientific research allows us to do this too. Beyond nice comparisons, however, being able to deepen the anatomical structures and behaviors of an animal with such a complex sociability is very important. Understanding how they developed their communication system will not only allow us to keep their species more efficiently, but it will guarantee us a new reading key to also analyze the way the voice communication varies according to the animal group.

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