More than 50 species previously thought to be dumb make sounds, new study finds



CNN

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

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

Gabriel Jorgewich-Cohen, the publication’s principal investigator and a PhD student at the University of Zurich, told CNN the idea for the research came about when he read about a project in Brazil’s Amazon rainforest. In 2014, a study found that South American giant tortoises found in the Amazon use voice communication to talk to each other, including calling their offspring.

Hearing mother turtles call their young made Jorgewich-Cohen “super interested” in identifying more turtle sounds, he said. “I thought maybe there were more turtles making sounds.”

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

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

The idea quickly turned into a larger research project. “The idea was to focus on animals that are generally, historically, considered unvocalized,” he said. “I wanted to dig deeper into reporting these animals that aren’t known to vocalize and try to understand that as a whole.”

Each species was recorded for at least 24 hours. Audio recordings include clicks, chirps, hisses and hums.

He added tuataras after speaking with a New Zealand reptile specialist who said she heard the animals making sounds during fieldwork. Audio recordings used in the research document the tuatara’s distinctive crackling vocalizations.

The sounds made by caecilians were particularly unexpected, he said. “I was very surprised to discover that they often produce sounds and in a very funny way,” he said. Caecilian recordings sometimes sound like a purr, and at others like a loud burp.

He was also surprised by the vast repertoire of certain species: Some turtles “made many different kinds of sounds.” Others, even though they had a more limited vocabulary, “wouldn’t stop chattering”, frequently repeating the same sounds.

And the research may have wider implications for our understanding of biology. Historically, “the main assumption was that the sounds made by frogs, 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 despite having different origins.

But the extensive evolutionary family tree constructed by Jorgewich-Cohen’s research team suggests that the ability to produce sounds “comes from a 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), around 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 ecology and evolutionary biology professor John Wiens and Zhuo Chen in Nature Communications in 2020.

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

Jorgewich-Cohen’s research just shows that turtles and other species make sounds — not that they use 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 sounds are actually meaningful communication will take more research, Wiens said. He pointed to playback experiments, such as when researchers play recordings of two different male frogs to a female frog to see which attracts her more. Experiments like these provide more meaningful evidence that sounds are actually used for communication, according to Wiens.

And the criteria for what scientists identified as acoustic communication were unclear, he said. “In some of these cases, it’s hard to tell they’re making sounds,” Wiens said.

Still, the article is helpful in showing that the animal world is indeed more talkative than scientists previously thought.

“They documented more sound-producing things that people had previously enjoyed,” Wiens said. “That’s the first step.”

The next step should be to implement reading experiments and other tests “to determine whether or not they have acoustic communication,” he said.

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

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

And “on top of that, I’d like to understand a bit of their cognitive ability – how they think, more than actually what the sounds mean.”

Additionally, understanding the role sound plays in the lives of turtles could aid conservation efforts.

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


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