51����

Stingrays have been documented making strange clicking sounds in the wild by scientists.

at the Swedish University of Agricultural Sciences and his colleagues have recorded individuals of two stingray species, the mangrove whipray (Urogymnus granulatus) and the cowtail stingray (Pastinachus ater), making the noises.

Stingrays, which are cartilaginous fish like sharks, are generally considered to be silent, but there have been a few anecdotal reports of them making noises under or .

So Fetterplace and his colleagues set out to investigate the phenomenon in oceans off the coast of Indonesia and Australia. The team managed to record mangrove whipray and cowtail stingray individuals making clicking sounds for a minute or two as a diver swam in towards them.

“We didn’t think that stingrays had the anatomy to make sounds,” says Fetterplace. “It’s kind of amazing because it shows that there are so many things in the ocean we don’t actually know.”

Stingrays have recently been shown to make but Fetterplace says the noises that his team have recorded are unlikely to be related to eating. “We didn’t see any evidence that they were chewing food,” he says. “Also, there’s a pattern in the sound with a constant beat going through it – which you don’t really expect in chewing sounds.”

It is unclear why the stingrays make the sounds. “My educated guess would be that they’re doing it as a warning,” says Fetterplace. “It could be used to physically startle something like a shark.”

“They might also be communicating to other rays that there’s danger,” he says.

“Although there has been some anecdotal evidence before this paper, it is the first one to actually present a recorded sound and some acoustic information,” says at the University of Exeter, UK. “I hope it will encourage researchers to focus on the acoustic ecology of these animals.”

The phenomenon may not have been more widely observed because stingrays only make the clicking sound rarely or maybe only certain species of stingray can make them, says Fetterplace.

He says people have already reached out to him to say they have heard stingrays make similar sounds and some have video footage. He plans to collate and analyse these reports. “If you have an example of stingrays making sounds – please send it to us,” he says.

But divers shouldn’t seek out stingrays to hear these noises, he says. “Stingrays are not aggressive unless they’re threatened. But if they are threatened, they have the potential to hurt you.”

Sign up to Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth’s other weird and wonderful inhabitants