Dolphins’ echolocation based on reverberations through skull?

Abstract

The sensitivity of odontocetes to changes in sound source azimuth and, in particular, elevation (minimum audible angles) has been reported to be superior to those of humans and bats. It has been suggested that binaural/spectral cues might be insufficient to account for this skill. We investigate bone-conducted sound in a short-beaked common dolphin’s mandible and attempt to determine whether and to what extent it could contribute to the task of localizing a sound source. Experiments are conducted in a water tank by deploying, on the horizontal and median planes of the skull, sound sources that emit synthetic clicks between 45 and 55 kHz. Elastic waves propagating through the mandible are measured at the pan bones and used to localize source positions via binaural cues, as well as a correlation-based full-waveform algorithm. We find that by making use of the full waveforms, and, most importantly, of their reverberated coda, the accuracy of source localization in the vertical plane can be enhanced. While further experimental work is needed to substantiate this speculation, our results suggest that the auditory system of dolphins might be able to localize sound sources by analyzing the coda of biosonar echoes.