Ultrasonic Frogs Raise the Pitch

Some frogs that live in noisy streams communicate by using ultrasonic calls.

Cartoon superheroes have included bats, spiders, and turtles. It may be time to add frogs to the list of animals that have special powers.

Scientists have found signs of ultrasonic communication in a frog species that lives in China. Ultrasonic signals have such a high pitch that people can’t hear them. This type of frog is the first amphibian ever discovered to have such sensitive ears.

A concave-eared torrent frog.

Courtesy of Albert Feng.

Concave-eared torrent frogs are small and brown. They make a variety of noises, including some that people can hear. Their calls sound like bird whistles and chirps.

Using equipment designed to study the very high-pitched bleeps that bats make, scientists have found that the frog calls also include very high-pitched chirps that topped 20 kilohertz (20,000 cycles per second)—sound frequencies that people can’t hear.

Concave-eared torrent frogs are found on a mountainside next to a rock-filled stream at China’s Huangshan Hot Springs. When scientists visited the site, they discovered that the noise from water rushing over the rocks was so loud that they had to shout all the time to hear each other.

The researchers suspected that ultrasonic signaling would allow these frogs to hear each other over the babbling racket. To test this idea, they played recordings of different parts of a frog’s calls. When they played just ultrasonic parts, a male frog responded immediately by calling back. A few other males called, too, though not as soon afterward.

An illustration of a concave-eared torrent frog.

Margaret Kowalczyk

Next, the scientists tested the brains of some of these frogs. Their results showed that frog nerve cells are sensitive to frequencies as high as 34 kilohertz.

This finding suggests that torrent frogs can actually hear ultrasonic sounds and probably use them to communicate. Other frogs normally hear only much lower pitches.—E. Sohn

Going Deeper:

Milius, Susan. 2006. Can you hear me now? Frogs in roaring streams use ultrasonic calls. Science News 169(March 18):165-166. Available at http://www.sciencenews.org/articles/20060318/fob6.asp .

For additional information about ultrasonic frogs, go to www.news.uiuc.edu/news/06/0315frogs.html (University of Illinois).

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