While male Odorrana tormota frogs are known to communicate in the ultrasonic range, the females do not respond to these frequencies, reports a study in Nature Communications this week. This shows that ultrasonic hearing has evolved as a form of communication only in the male frogs.Jun-Xian Shen and colleagues performed acoustic experiments by playing back male mating calls to female O. tormota frogs. They recorded a reaction from the females to calls in the normal range, but not in the ultrasonic range of above 20 kHz. This finding was confirmed by further electrophysiological studies of the female’s auditory midbrain with no response seen in the ultrasonic range.