Chinese frog that sings like a bird

Noisy waterfalls and claps of thunder can drown out even the most vocal frog. But some persistent croakers in China have a clever fix: They switch to ultrasound.

Photo: Chinese frog that sings like a bird

The feat, researchers say, makes the frogs the first amphibians to be placed alongside an exclusive group of mammals, such as whales and dolphins, that have ultrasonic ability.

"It shows a new example of independent evolutionary adaptation in the frogs for life in habitats filled with loud background noise," said Albert Feng, a professor of neuroscience at the University of Illinois, Urbana-Champaign. Researchers first heard of the unusual animals in 2000 from Kraig Adler, a biologist at Cornell University.

He tipped the scientists off to Huangshan Hot Springs, a popular tourist destination near Shanghai, where he had found frogs with recessed ears.

"I noticed the frogs' sunken ears and thought they must have an odd system of communication. We had no idea they used ultrasonic sounds," Adler said, reports National Geographic.

A frog that sings like a bird has been found to have another unusual trait - it can communicate in high-pitched squeaks that are inaudible to the human ear. The frog lives in the fast-moving streams and waterfalls of east-central China and uses ultrasonic calls to make itself heard above the noise of running water.

The human ear cannot hear sounds with frequencies higher than 20 kilohertz but the frog has been recorded emitting sounds higher than 128kH which can carry above the noise of splashing water. "Nature has a way of evolving mechanisms to facilitate communication in very adverse situations," said Professor Albert Feng of the University of Illinois at Urbana-Champaign.

"One of the ways is to shift the frequencies beyond the spectrum of background noise. Mammals such as bats, whales and dolphins do this, and use ultrasound for their sonar system and communication," he said.

The frog - Amolops tormotus - has an unusually recessed ear canal which protects a thin and delicate eardrum that can detect high-frequency sounds, Professor Feng said. "Thin eardrums are needed for detection of ultrasound. Recessed ears shorten the path between eardrums and the ear, enabling the transmission of ultrasound to the ears," he said, informs Independent.

O.Ch.