Auditory Thresholds of a Fresh Water Dolphin, Inia geoffrensis Blainville

A fresh water Amazon River dolphin, Inia geoffrensis, was conditioned to respond to pure tones by pushing a response lever. By using this method an audiogram was obtained for frequencies between 1.0 and 105 kHz. The animal was most sensitive to tones between 75 and 90 kHz. The sensitivity threshold in this area was −50 dB re 1 dyn/cm². The effective upper limit of hearing was 105 kHz. No reliable response was elicited above 105 kHz using a random presentation and undistorted signal.