Sound localization by the bottlenose porpoise Tursiops truncatus

Abstract

1. Sound localization was measured behaviourally for the Atlantic bottlenose porpoise (Tursiops truncatus) using a wide range of pure tone pulses as well as clicks simulating the species echolocation click. 2. Measurements of the minimum audible angle (MAA) on the horizontal plane give localization discrimination thresholds of between 2 and 3 degrees for sounds from 20 to 90 kHz and thresholds from 2–8 to 4 degrees at 6, 10 and 100 kHz. With the azimuth of the animal changed relative to the speakers the MAAs were 1-3-1-5 degrees at an azimuth of 15 degrees and about 5 degrees for an azimuth of 30 degrees. 3. MAAs to clicks were 0-7-0-8 degrees. 4. The animal was able to do almost as well in determining the position of vertical sound sources as it could for horizontal localization. 5. The data indicate that at low frequencies the animal may have been localizing by using the region around the external auditory meatus as a detector, but at frequencies about 20 kHz it is likely that the animal was detecting sounds through the lateral sides of the lower jaw. 6. Above 20 kHz, it is likely that the animal was localizing using binaural intensity cues. 7. Our data support evidence that the lower jaw is an important channel for sound detection in Tursiops.