for National Geographic News
Tree-dwelling frogs that live near the noisy Huangshan Hot Springs of China stage intricate courtship musicals at frequencies far beyond the range of human hearing, according to a new study.
A team of Chinese and American scientists found that the frogs communicate their symphony of mating calls ultrasonically.
The researchers, led by Shen Junxian of the Chinese Academy of Science, used microphones to record the mating calls emitted by female torrent frogs on rainy nights just before ovulation.
When the ultrasonic recordings were played back to a group of male torrent frogs, they responded by singing in synchrony with the female lead and then leaping toward the source of the call with pinpoint accuracy.
The scientists say that using ultrasonic calls allows the frogs to communicate clearly despite the background of crashing mountain waterways. (Related: "Ultrasonic Frogs Discovered in China Make 'Silent' Calls [March 16, 2008].)
The frog, Odorrana tormota, joins select species of birds, along with dolphins and whales, that are known to communicate ultrasonically to circumvent background noise, said study co-author Albert Feng, a physiologist at the University of Illinois at Urbana-Champaign.
The findings appear online this week in the journal Nature.
According to the authors, female frogs make the first overture with a courtship call featuring multiple harmonics that extend into the ultrasonic range—frequencies greater than 20 kilohertz, the upper limit of human hearing.
Like a soprano in a human opera, the female torrent frog's call "has a much higher fundamental frequency than her male counterpart's," said study co-author Peter Narins, a professor of physiological science at the University of California, Los Angeles.
This opening solo often triggers a quick "antiphonal response" by a nearby male, which issues a series of lower-pitched ultrasonic calls in return.
This musical dialogue resembles melodic exchanges between birds or human singers.
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