Scientists have discovered how Amolops tormotus, AKA the concave-eared torrent frog, makes itself heard above the gushing waterfalls of its habitat in east-central China: bat-style ultrasound.

The discovery, detailed in today's issue of journal Nature, makes this particular crazy frog the first non-mammal known to use ultrasonic communication. Researchers have known for several years that the males produce high-pitched, birdlike calls that extend into the ultrasonic range. Whatremained to be tested was whether the sounds were a byproduct of the frog's sound production, or were actually listened to and responded to.

The University of Illinois-UCLA team first wanted to know if the frog can hear very high frequencies. They recorded a male's call, split it into the audible components and ultrasonic components, and observed the responses of eight other males. The behavioural results showed they heard and responded.

The finding was then confirmed by measuring electrical activity in the frog's mid-brain - where sound is processed.

Since most frogs lack the concave-eared torrent frog's ear canal, the researchers say their findings bolster the idea that the canal evolved to detect high frequencies.

The work was part-funded by the US National Institute on Deafness and Other Communication Disorders. Director James F. Battey explained the apparently tenuous link: "The more we can learn about the extraordinary mechanisms that Amolops and other animals have developed to hear and communicate with one another, the more fully we can understand the hearing process in humans, and the more inspired we can be in developing new treatments for hearing loss." ®