What sound does a turtle make?

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Some animals are famous for the sounds they make - birds and their songs, frogs and their ribbits. But have you ever heard of a talkative turtle? Well, most turtles were thought to not make sounds at all until researchers went deep, as NPR's Laurel Wamsley reports.

LAUREL WAMSLEY, BYLINE: Do turtles talk? What about other lesser-known vertebrates? The answer is yes, according to a new paper in Nature Communications presenting evidence that many species thought to be mute do in fact vocalize. And the researchers caught it on tape. Here's a Southern New Guinea giant softshell turtle.

(SOUNDBITE OF TURTLE GURGLING)

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WAMSLEY: And here's a caecilian, a limbless amphibian that lives hidden underground.

(SOUNDBITE OF CAECILIAN SNORTING)

WAMSLEY: Gabriel Jorgewich-Cohen is lead author of the paper and an evolutionary biologist working on his Ph.D. at the University of Zurich. The project got started after he read about a turtle in the Amazon making sounds, and he started wondering about the little sounds his own pet tortoises made. He got in touch with a researcher at his former university in Brazil.

GABRIEL JORGEWICH-COHEN: He developed a type of hydrophone, which is pretty much a microphone that goes underwater. And I started recording my own pets, and I actually heard them making a lot of noises.

WAMSLEY: It was on. He traveled to eight or nine institutions in five countries on a quest to record animal species that were thought mostly to be mute. He recorded 50 kinds of turtles as well as tuataras, caecilians and lungfish. And it turned out none of them were mute.

JORGEWICH-COHEN: Actually, every single animal I recorded made sounds.

WAMSLEY: He says the findings point to a common ancestor some 400 million years ago. Neil Kelley is a paleontologist at Vanderbilt University.

NEIL KELLEY: Sometimes it's surprising how much we still don't know about things that aren't necessarily uncommon but live alongside us.

WAMSLEY: Kelley says the paper's conclusion mapping these vocalizations onto the evolutionary tree makes sense. He notes there are unique challenges to studying animal sounds evolutionarily.

KELLEY: It's very hard to trace that in the fossil record because sounds obviously don't fossilize. And most vocal equipment is soft tissue-based.

WAMSLEY: And it's important to note that sound production and hearing are different things. Snakes, for example, are famous for their hissing sounds, but they aren't thought to be able to hear themselves or each other hissing. And a turtle making sounds doesn't necessarily mean that it's communicating that way, says John Wiens, an evolutionary biologist at the University of Arizona.

JOHN WIENS: I think there's some conflation of making sounds and acoustic communication.

WAMSLEY: Jorgewich-Cohen says that while they aren't sure what all the sounds mean, they used several strategies to identify sounds used for communication, such as using cameras to correlate sounds with behaviors that could demonstrate some kind of intention. Wiens says the recording of these sounds is an important step toward further understanding.

JORGEWICH-COHEN: If you don't record these sounds and, you know, report them, there's no reason why anybody would study acoustic communication in those things, right? You don't even know that they're making sounds.

WAMSLEY: The next step, he says, is figuring out what all these animals might actually be saying. Laurel Wamsley, NPR News.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.