Ultrasonic frogs found in China
A small Chinese frog species has been found to use ultrasound to communicate. Bats and dolphins and a few other species emit and hear ultrasonic noises but these are the first amphibians to have been found to have the capacity to do so. The research team was led by Albert S. Feng & M. Kowalczyk, University of Illinois at Urbana-Champaign.
The frog species is the Amolops tomotus, the "concave eared torrent frog." As its name suggests, it has an unusual ear which is recessed rather than protruding. (The ear shape may be related to the frog's hearing capacity, according to Feng). The "torrent" refers to its usual environment.
The frogs live on a mountainside by a rock-filled stream, at Huangshan Hot Springs. These surroundings tend to be very noisyThe research team found that they had to shout to communicate beacuse the noise of the water rushing over the rocks was so loud.
The researchers suggested that the high level of environmental noise is what prompted the frogs to develop ultrasound sending and receiving capacities, as a means of communication with each other. (Nature, March 16 2006)
The frog emits a wide range of audible sounds. It sounds like a bird to the human ear. However, sonograms showed that the frog also emits sounds above 20 khz, at a higher frequency than the noise produced by the waterfall as well as beyond the range of human hearing. Frogs responded to recordings of the high pitched sounds by emitting calls, demonstrating that the frogs could indeed hear sounds at these frequencies. Experiments with electrodes in the frogs' brains showed that they could respond to sounds of up to 34 khz.