Frog's Ears Can Switch Frequencies Like Radios

July 22, 2008 -- Just as humans tune into individual radio stations, an unusual Chinese frog can shift its hearing from one frequency to another in order to selectively choose what it hears, according to a paper published in this week's Proceedings of the National Academy of Sciences.

The frog, Odorrana tormota, is the only known animal in the world that can manipulate its hearing system to select particular frequencies. Humans appear to possess a modicum of control, but our system is slow compared to that of the frog and we cannot, with precision, tune our ears to match sounds.

The rare amphibian likely evolved its hearing talent out of necessity, since its environment is so noisy.

"Their calling sites are on the steep banks of a fast-flowing body of water -- the Tao Hua Creek (at Huangshan Hot Springs in central China)," co-author Albert Feng told Discovery News.

Feng, a professor of molecular and integrative physiology at the University of Illinois at Urbana-Champaign, added that the site is especially noisy after spring showers. He pointed out that humans often cannot hear well over heavy rains either.

"We pretty much have to shout at one another," he said.

The frog doesn't shout, but it instead sings like a bird either in audible chirp-like frequencies or by emitting very high-pitched ultrasonic sounds.

Curious as to how the amphibian could hear these different vocalizations, Feng and his team analyzed the frog's hearing system, which wasn't too challenging since the frog's eardrum is completely transparent.

The scientists used a laser to measure the eardrum's vibration, and noticed that while it could respond to both audible and ultrasonic sounds, sometimes the eardrum's sensitivity to ultrasonic noise mysteriously disappeared.