Hypersonic Frog

A small frog species from China is the first amphibian shown to use ultrasonic calls. The male concave-eared torrent frog can hear extraordinarily high frequencies with its unusual, recessed ear (arrow and inset), an advantage for life in a noisy place. Equipment designed for studying bats picked up high-pitched chirrups in the calls of the concave-eared torrent frog Amolops tormotus, says Albert S. Feng of the University of Illinois at Urbana-Champaign. He and his colleagues also measured nerve activity in the hearing centers of the frog brains in response to ultrasonic tones.

The small brown frogs live beside water splashing over rocks on a mountainside in Huangshan Hot Springs, China. Ultrasonic perception may have developed as the frogs struggled to hear each other over the din, the researchers suggest in the March 16 Nature.

High-pitched signaling is "absolutely unexpected," says Michael Ryan of the University of Texas at Austin, who studies frogs and frog-eating bats.