Scientists Thought These 53 Species Were Silent. Now, They’ve Recorded Their Sounds

As a toddler might eagerly tell you, owls hoot, dogs bark and cows moo. But when it comes to turtles, for example, even scientists would have struggled to say what sound they make. Until now, researchers had assumed a whole slew of species were silent.

But new research, published last week in Nature Communications, suggests that at least 53 of those creatures previously thought to be soundless are actually communicating with vocalizations.

“We know when a bird sings,” says study co-author Gabriel Jorgewich-Cohen, an evolutionary biologist at the University of Zurich in Switzerland, to BBC News’ Georgina Rannard. “You don't need anyone to tell you what it is. But some of these animals are very quiet or make a sound every two days.”

While studying turtles in the Amazon rainforest, Jorgewich-Cohen began to wonder if scientists had actually gotten it wrong by assuming that the shell-inhabiting reptiles were silent. When he got home, he decided to listen for vocalizations of his own pets, including Homer, a turtle he’s had since he was a child.

To his surprise and delight, he successfully recorded his pet turtles making several sounds. After that, he decided to broaden his experiment to include many other species that scientists once considered to be non-vocal.

Juvenile South American river turtles

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All told, he captured sounds from 50 species of turtles, as well as the lizard-like reptile called the tuatara, the worm-like amphibian known as the Cayenne caecilian and the air-breathing South American lungfish. The creatures made a variety of different sounds, including grunts, chirps, snorts and clicks, to name a few. Some were very chatty, while others made only a few peeps every ten hours. Nearly all the species had never been recorded making sounds before.

The scientists also used underwater cameras to capture videos of the behaviors linked to each vocalization. They found that male species often made sounds while wooing females or while fighting with other males; some of the animals also made sounds to defend their territory.

The findings suggest that acoustic communication among nose-breathing choanate vertebrates may have evolved from a common ancestor some 407 million years ago. To reach that conclusion, the scientists combined their new data with earlier research on the evolutionary history of acoustic communication in 1,800 other species.

Based on their a phylogenetic, or family tree, analysis, the researchers propose that this common ancestor may have been the lobe-finned fish known as Eoactinistia foreyi, which lived during the Devonian era, when much of life was underwater.

“What we found is that the common ancestor of this group was already producing sounds and communicating using those sounds intentionally,” Jorgewich-Cohen tells the Agence France-Presse.

Still, not everyone is convinced that vocalization arose from a common ancestor. After all, researchers came to the opposite conclusion in 2020—that acoustic communication developed in various species independently and repeatedly within the last 100 to 200 million years. Plus, it’s possible that the noises made by these 53 species don’t qualify as communication.

Since fossils can’t capture sounds, scientists will need to perform additional research to confirm their conclusions. But in the meantime, the findings show that it’s worth taking another look—or, rather, another listen—at long-accepted scientific conclusions. Indigenous communities and other citizen scientists may also be able to share their vast knowledge of hard-to-study creatures.

“The data might already be out there in some form if we just start to think more carefully about who we should be listening to,” says Irene Ballagh, a zoologist at the University of British Columbia in Canada who was not involved with the study, to Scientific American’s Rachel Nuwer.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.