US researcher Albert Feng and his colleagues have found that a species of Chinese frog that lives in a noisy environment has evolved a clever way to prevent its croaks being drowned out by the sound of nearby running water - it croaks in ultrasound. The researchers discovered the strange vocal habits of the concave-eared torrent frog, which lives in a mountainous region of China, by accident when they used sensitive recording equipment to monitor the frogs activity. As well as croaking the conventional way, these frogs were also producing very high pitched noises, inaudible to humans. When the researchers recorded the sounds and played them back to captive frogs they found that their study subjects croaked in unison with the recording. To find out how the frogs were responding to the ultrasound the researchers then temporarily blocked up their ears, instantly stopping the karaoke. Feng and his team believe that the sounds are a mating call designed to cut through the loud noises of running water which are prevalent in the frogs aquatic environment. They are now eager to track down some females to see how they respond to an ultrasonic "ribbet".


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