March 17, 2006 — A rare frog uses ultrasonic sound to communicate with its brethren, a clever tool that helps it overcome the noise of the waterfalls it inhabits, researchers in the U.S. and China have found.

The concave-eared torrent frog (Amolops tormotus) joins bats, dolphins and whales and a small number of rodents in the elite club of creatures that are able to communicate by ultrasound.

A team led by Albert Feng of the University of Illinois found that male frogs of this species make high-pitched melodic bird-like calls that sometimes exceeded their recorder's maximum range of 128 kilohertz — more than six times the limit of human hearing.

The frogs inhabit Huangshan Hot Springs, a popular mountainous area west of Shanghai, where there are loud waterfalls and streams.

The high frequencies provide a channel of communication that cannot be disrupted by the lower-frequency rumble of the water, said Feng.

"Nature has a way of evolving mechanisms to facilitate communication in very adverse situations," he said.

"One of the ways is to shift the frequencies beyond the spectrum of the background noise. Mammals such as bats, whales and dolphins do this, and use ultrasound for their sonar system and communication. Frogs were never taken into consideration for being able to do this."

The discovery also answers a puzzle as to why the frogs do not have external eardrums.

"Thin eardrums are needed for detection of ultrasound," said Feng. "Recessed ears shorten the path between the eardrums and the ear, enabling the transmission of ultrasound to the ear."

The paper appears on Thursday in Nature.

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