Primate communication in the pure ultrasound

This study published last month sheds new light on ultrasonic communication. Frequencies above 20 kHz, the human boundary for hearing, are classified as ultrasonic. While some primates have been known to emit partially ultrasonic vocalizations, there has been little evidence of purely ultrasonic primate communication. In the study, the auditory brainstem response (ABR) method was used to estimate auditory sensitivity in six Philippine tarsiers (T. syrichta). Additionally, the calls of 35 wild tarsiers were recorded with an ultrasound recording unit. The tarsiers' high frequency auditory limit was estimated to be 91 kHz, shattering the primate record of 65 kHz in the bush baby. Moreover, eight individuals' vocalizations were determined to be purely ultrasound. These results suggest that T. syrichta can communicate purely in the ultrasound, which may allow for private communication undetectable to predators, prey, or competitors.