Female Turtles “Talk” to Their Hatchlings, Scientists Discover

A giant South American river turtle. Photograph by Joel Sartore, National Geographic Creative

The first time Richard Vogt tried to catch a giant South American river turtle (Podocnemis expansa), the hundred-pound (45-kilogram) reptile dragged him 30 feet (9.1 meters) down to the bottom of a river. It would have kept going, too, if he hadn’t decided to give up and let go of the shell.

Vogt is a herpetologist with Brazil’s National Institute for Amazonian Research who recently received the ninth annual Behler Turtle Conservation Award for lifetime achievement. Twenty-five years after that giant first pulled him under, he’s still studying these fascinating creatures. In fact, in the most recent issue of Herpetologica, the first known evidence that turtles provide parental care for their hatchlings was reported by Vogt and Camila Ferrara of the Wildlife Conservation Society. 

“The giant South American river turtle is one of the most social species of turtle in the world,” Vogt said. “They migrate together, they nest communally, and they hatch out in huge numbers together.”

And now, thanks to 220 hours’ worth of underwater recordings, Vogt and his team have shown that female giant South American river turtles in Brazil call to their hatchlings once they reach the water for the first time.

Pillow Talk

The very idea that turtles can communicate with each other using sound is rather new. Turtles lack vocal cords and their ears are internal, so for many years scientists simply assumed turtles were, as Vogt called it, “deaf as a post.”

Over the past 50 years of working with these animals, it always seemed strange to him that some species could seem so downright organized without some form of communication.

For instance, when giant South American river turtles (also known as Arrau river turtles) leave the water to dig a nest and lay eggs, they do so in single file. Vogt has witnessed a queue of females stretching 16 turtles long—though regrettably, that tally was reduced to 15 after a black caiman picked off the last in line.

In recent years, however, herpetologists have started to detect a whole host of sounds made by the reptiles, both in and out of the water.

“Not only are the turtles talking,” said Vogt, “they’re talking before they hatch.”

Vogt suspects that sounds made while the hatchlings are still in the shell may stimulate the group to emerge all at once. They may also account for the many premature hatchlings commonly found at the bottom of a nest. Presumably, the turtles hear their siblings’ calls and pop out before they’re physically ready.

Come to Mama!

Unlike other species that hatch en masse, such as sea turtles, giant South American river turtles don’t have to start their lives as orphans.

In fact, as soon as the tiny turtles hit the water for the first time, females that have been waiting in the area since they laid eggs two months ago start calling out to the babies. Once the two generations meet up, they migrate together from the beach back to the river’s flooded forests.

A photo of a Giant South American river turtle hatchling emerging from its shell.
A giant South American river turtle hatchling emerges from its shell. Photograph by C. Ferrara, Wildlife Conservation Society

The scientists aren’t sure yet if the females in the water are actually related to the hatchlings, but they plan to do blood tests later this year to determine whether an individual mother might somehow recognize and join up with her own offspring. A hatching event can mean thousands and thousands of babies hitting the water at the same time, so this kind of recognition would be all the more impressive.

Not Exactly Chatterboxes

One of the reasons it’s taken us so long to learn about these sounds is that turtles communicate at frequencies in the lower range of the human audible spectrum. Like whales, turtles probably use these frequencies because the sounds can travel long distances underwater.

It helps to have a young set of ears, because humans over the age of 50 have a difficult time detecting low-frequency sounds. Oh, and you’ll also need some patience. Vogt said you can place a hydrophone in the water next to a turtle and expect to hear only 15 to 20 sounds over the course of eight hours.

And it only works in the wild. “Take a turtle out of the wild and it’ll talk for a few days and then just shut up,” Vogt said.

So, what do turtles sound like? Vogt compares the sounds to clicks, clucks, and hoots.

Note that the individual sounds on these recordings have been amplified and repeated to enable the listener to better hear the differences in vocalizations. In the wild, the turtles make these individual sounds with long periods of silence in between. All recordings are by C. Ferrara of the Wildlife Conservation Society.

Cry for Help?

Now that we know giant South American river turtles rely on communication to enable hatching and migration, Vogt said it’s time to determine what effect shipping noise might have on the animals. There’s already plenty of evidence that the noise created by oil and gas exploration is detrimental to a wide variety of marine mammals, so perhaps turtles are also at risk. (See “Will Atlantic Ocean Oil Prospecting Silence Endangered Right Whales?”)

Unfortunately, this species is also under threat from the illegal wildlife trade and local appetites. Brazilians prize turtle eggs as a delicacy, and the turtles themselves are often slaughtered for meat. A recent trend toward dam building in the country rounds out the list of potential threats. (See also “Costa Rican Murder Shines Light on Poaching, Drug Nexus.”)

While the International Union for Conservation of Nature currently lists the giants as being of “Least Concern,” the Tortoise and Freshwater Specialist Group (of which Vogt is part) has strongly recommended a change in status to “Endangered.”

A Whole New Line of Inquiry

This sort of research is interesting not only for the effects it might have on our understanding of a particular species, but also for turtles in general.

“This research is exciting because it basically opens up a whole new line of inquiry related to turtle behavior,” said David Steen, a conservation biologist specializing in turtles and snakes at the Alabama Natural Heritage Program at Auburn University.

“That we know so little about the wildlife around us is exciting because it reinforces that one should never just accept conventional wisdom when conducting research,” Steen said. “We still have a lot to learn.”

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