A Japanese researcher has filmed a wrinkled frog croaking underwater in the northern city of Yamagata.
Kano Yuichi, an associate professor at Kyushu University, took the rare footage of the frog while he was conducting research in a river in June.
The frog was calling by shaking its belly, without using its vocal sac. Analysis revealed that the croaks came at shorter intervals and were lower pitched than those made on land.
The wrinkled frog is found in many areas of Japan. The male frogs pop their heads out of shallow water during the rainy season to call out to females by inflating their vocal sacs.
Kano says wrinkled frogs may be making their calls underwater to avoid being spotted by predators. He says scientists have not paid much attention to them before and this may be the reason why they didn't know about the underwater croaking.
Kano says that many researchers are surprised when he shows them his video. He says it's interesting there are still many things people don't know about familiar creatures and he wants to continue his investigation.