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Over 50 species previously thought to be mute make sounds, according to a new study

<i>Gabriel Jorgewich Cohen</i><br/>Species like the big-headed Amazon River turtle shown here have been found to make sounds
Gabriel Jorgewich Cohen
Gabriel Jorgewich Cohen
Species like the big-headed Amazon River turtle shown here have been found to make sounds

By Zoe Sottile, CNN

If you listen closely, your pet turtle might just have something to say to you.

A new study published in Nature Communications has identified sounds made by 53 species, many of which were previously thought to be mute. Fifty of the species were turtles, with tuataras (a kind of reptile found in New Zealand), caecilians (a limbless amphibian), and the South American lungfish rounding out the group.

Gabriel Jorgewich-Cohen, the lead researcher on the publication and a PhD student at the University of Zurich, told CNN that the idea for the research was born when he read about a project in Brazil’s Amazon rainforest. In 2014, a study found that Giant South American river turtles found in the Amazon use vocal communication to speak to each other — including calling to their offspring.

Hearing the mother turtles calling to their young made Jorgewich-Cohen “super interested” in identifying more turtle noises, he said. “I thought maybe there are more turtles out there making sounds.”

The biologist then began collaborating with a professor who developed specialized sound equipment for recording underwater. He started at home, recording his own pet turtles. “At first, I didn’t expect to find anything,” he said.

But contrary to his expectations, he “found a lot of sounds,” he said.

The idea soon expanded into a larger research project. “The idea was to focus on animals that are commonly, historically considered to be nonvocal,” he said. “I wanted to go deep on reporting these animals that are not known to vocalize, and try to understand this in the big picture.”

Each species was recorded for at least 24 hours. The audio recordings include clicking, chirping, hissing, and purring.

He added in tuataras after speaking with a specialist on the New Zealand reptiles who said she had heard the animals making sounds during fieldwork. The audio recordings used in the research document the tuatara’s distinctive crackly vocalizations.

The sounds made by caecilians were especially unexpected, he said. “I was very surprised to discover they do produce sounds often, and in a very funny way,” he said. The caecilian recordings sound at times like purring, and at others like a loud burp.

He was also surprised by the broad repertoire of some species: Some turtles “made many different types of sounds.” Others, although they had a more limited vocabulary, “wouldn’t stop chatting,” frequently repeating the same sounds.

And the research may have broader implications for our understanding of biology. Historically, “the main hypothesis was that the sounds made by frogs and birds and mammals all came from different evolutionary origins,” Jorgewich-Cohen explained. This phenomenon is known as convergent evolution, when species adapt in similar ways although they have different origins.

But the extended evolutionary family tree constructed by Jorgewich-Cohen’s research team suggests that the ability to produce sounds “comes from one single origin,” he said. The paper claims that vocal communication must be as old as the last common ancestor of choanate vertebrates (vertebrates with lungs), approximately 407 million years old.

In addition to recording 53 species themselves, Jorgewich-Cohen and his team also used an acoustic communication dataset published by University of Arizona professor of ecology and evolutionary biology John Wiens and Zhuo Chen in Nature Communications in 2020.

Wiens, who was not consulted for Jorgewich-Cohen’s study, told CNN that further research is needed to establish the common origins of vocal communication.

Jorgewich-Cohen’s research just shows that the turtles and other species are making sounds — not that they are using those sounds to communicate with each other, he said. In the article, Jorgewich-Cohen and his team wrote that “the presence of a complex repertoire (presence of a number of different sounds and/or harmonic calls)” indicated “communicative meaning.”

Establishing that the sounds are actually meaningful communication will require more research, Wiens said. He pointed to playback experiments, like when researchers play recordings of two different male frogs for a female frog to see which attracts her more. Experiments like those provide more meaningful evidence that the sounds are actually used for communication, according to Wiens.

And the criteria for what the scientists identified as acoustic communication weren’t clear, he said. “In some of these cases, it’s hard to tell they’re making sounds at all,” said Wiens.

Still, the article is helpful for showing that the animal world is indeed chattier than scientists thought before.

“They’ve documented more things making sounds than people had appreciated previously,” Wiens said. “That’s the first step.”

The next step should be to implement playback experiments and other tests “to figure out if they have acoustic communication or not,” he said.

Going forward, Jorgewich-Cohen says he hopes to decipher what turtles are actually saying to each other — if anything.

“In most cases, we just know they’re making sounds. We don’t know what they mean,” he said.

And “besides that, I would like to understand a bit about their cognition ability — how they think, more than actually what the sounds mean.”

What’s more, understanding the role sound plays in turtles’ lives might help contribute to conservation efforts.

“Turtles are the second most endangered group of vertebrates, behind primates,” he said. “When we think about their conservation, we never consider human noise as a source of problems, and I think maybe now we should start considering it, rethinking how we do conservation.”

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