EVERY child learns that frogs go 鈥渞ibbit鈥�, but no one suspected that they do it at ultrasonic frequencies. The concave-eared torrent frog (Amolops tormotus) now joins the select band of mammals 鈥� bats, dolphins and a few rodents 鈥� that communicate using ultrasound.
Albert Feng of the University of Illinois at Urbana-Champaign and colleagues found that the frog, which lives by a fast-flowing stream near Huangshan Hot Springs in eastern China, makes and responds both to sounds detectable by humans and those at ultrasonic frequencies 鈥� above 20 kilohertz, the maximum for human hearing (Nature, vol 440, p 333).
The researchers think the frog uses ultrasound to communicate in the dark through the din of its stream habitat. Background noise covers most of the audible frequency range. The finding could also explain the unique, recessed eardrum that gives the frog its common name, Feng says.
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To enable ultrasound to be transmitted into the ear, the frog鈥檚 eardrum is very thin, and the bones of the middle ear extremely small. The recessed position of the eardrum makes this possible by minimising the size of the middle ear.
Females鈥� ears are not recessed, suggesting that they don鈥檛 hear ultrasound and that the calls are used in interactions between males.
