Study identifies emission of sounds in species previously considered mute

If you listen carefully, your pet tortoise might have something to tell you.

a new study published in Nature Communications identified sounds made by 53 species, many of which were previously thought to be mute. Fifty of the species were tortoises, 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, lead researcher for the publication and a doctoral student at the University of Zurich, told CNN that the idea for the research was born when he read about a project in the Brazilian Amazon rainforest.

In 2014, one study found that South American giant tortoises found in the Amazon use vocal communication to talk to each other — including calling for their young.

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

The biologist then began to collaborate with a professor who developed specialized sound equipment for underwater recording. 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 non-vocal,” he said. “I wanted to dig deeper into reporting these animals that are not known to vocalize and try to understand that in the big picture.”

Each species was recorded for at least 24 hours. Audio recordings include click, chirp, hiss and purr.

He added tuataras after speaking with a reptile expert from New Zealand who said she heard the animals making sounds during fieldwork. The audio recordings used in the research document the tuatara’s distinctive cracked vocalizations.

The sounds made by the Cecilias were especially unexpected, he said. “I was very surprised to find that they make sounds often and in a very funny way,” he said. Cecilia’s recordings sometimes sound like a purr and sometimes like a loud burp.

He was also surprised by the wide repertoire of some species: some turtles “make many different types of sounds”. Others, although they had a more limited vocabulary, “wouldn’t stop talking”, often 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, birds and mammals came from different evolutionary origins,” explained Jorgewich-Cohen. This phenomenon is known as convergent evolution, when species adapt in similar ways even though they have different origins.

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

animal communication

In addition to recording 53 species, Jorgewich-Cohen and her team also used an acoustic communication dataset published by University of Arizona professor of ecology and evolutionary biology John Wiens and Zhuo Chen. at 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 vocal communication.

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

Establishing that sounds are indeed meaningful communication will require more research, Wiens said. He pointed to breeding experiments, such as when researchers play back recordings of two different male frogs for a female to see what attracts her the most.

Experiments like these provide more significant evidence that sounds are actually used for communication, according to Wiens.

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

Still, the paper is helpful in showing that the animal world is actually more chatty than scientists previously thought.

“They documented more things making sounds than people had previously realized,” said Wiens. “This is the first step.”

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

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

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

And “besides, I’d like to understand a little bit about their ability to cognition — how they think, more than really what sounds mean.”

In addition, understanding the role that sound plays in turtles’ lives can help contribute to conservation efforts.

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