Frogs on call

Nocturnal tree frogs living in China have been found to possess extraordinary vocal and localization skills, comparable to dolphins, elephants and humans. A paper online in Nature this week analyses the ultrasonic mating calls of the female torrent frog Odorrana tormota to reveal a surprisingly well-developed acoustic communication system, which is an adaptation to the noisy environment of rushing streams.

Vocalized mating calls play a key role in frog reproduction ? male frogs are typically dominant, advertising their virility, with the females tending to be more passive, occasionally producing a weak reciprocal call or rapping sounds during courtship. Although the females have an unusually well-developed vocal production system, whether or not they produce calls in a communication system dominated by males has so far been unclear.

Jun-Xian Shen and colleagues recorded the vocalizations of female frogs in a quiet, darkened room using an ultrasonic microphone linked up to a computer. They found that, just before ovulating, female frogs emit short, high-frequency ultrasonic signals distinct from the males’ advertisement calls. They then played back the female calls to examine the response of the male frogs, and found that they both increased their calling activity and approached the source of the noise. On hearing the female call, a male usually oriented his body and made a long-distance hop towards the loudspeaker with remarkable precision.

The authors suggest that the torrent frogs may have developed this high-frequency ultrasonic system as a method of unambiguous communication in the presence of their noisy habitat.