Ultrasonic frogs show hyperacute phonotaxis to female courtship calls

Ultrasonic communication: Female frogs on a high note The Chinese torrent frog, Odorrana tormota , a nocturnal tree-dweller in the noisy environment of rushing streams, has developed ultrasonic communication. New work reveals just how sophisticated the system has become. In most frog species, vocal advertisement is the domain of males. But in O. tormota the females emit ultrasonic signals when they are ovulating, and the males can locate their signals with an acuity of one or two degrees. That rivals the performance of vertebrates with the highest localization acuity — owls, dolphins, elephants and humans. The localization accuracy of O. tormota is all the more remarkable in light their small head size, and suggests an additional selection advantage of high frequency hearing beyond the ability to avoid masking by ambient noise. Sound communication plays a vital role in frog reproduction 1 , 2 , in which vocal advertisement is generally the domain of males. Females are typically silent, but in a few anuran species they can produce a feeble reciprocal call 3 or rapping sounds 4 during courtship. Males of concave-eared torrent frogs ( Odorrana tormota ) have demonstrated ultrasonic communication capacity 5 . Although females of O . tormota have an unusually well-developed vocal production system 6 , it is unclear whether or not they produce calls or are only passive partners in a communication system dominated by males. Here we show that before ovulation, gravid females of O. tormota emit calls that are distinct from males’ advertisement calls, having higher fundamental frequencies and harmonics and shorter call duration. In the field and in a quiet, darkened indoor arena, these female calls evoke vocalizations and extraordinarily precise positive phonotaxis (a localization error of