Acoustic Localization Method Applied to the Analysis of Dolphin Calf Acoustical Exploratory Behavior Within its Social Group

Abstract

Exploratory behaviour includes all the actions that an animal performs to obtain information about a new object, environment or individual through using its different senses of perception. Here, we studied the development of the exploratory behaviour of a bottlenose dolphin (Tursiops truncatus) calf aged from 39 to 169 days, by investigating its acoustic productions in relation to an immerged object handled by a familiar human without isolation from its original social group. The study was conducted between July 2015 and January 2016 at Parc Asterix dolphinarium (Plailly, France). Simultaneous audio and video recordings were collected using a waterproof 360° audio-video system named BaBeL which allows localization of the dolphin that is producing sounds. During 32 recordings sessions, for a total duration of 6 hours 55 minutes of audio-video recordings, 46 click trains were attached to individual dolphins: 18 times to the calf, 11 times to its mother and 17 times to another dolphin in the pool. When comparing the calf’s acoustical production to its mother’s, no significant differences were found in their click rate, mean click duration, or mean interclick interval (ICI). However, linear regression showed that calf’s click rate increased with age and mean ICI decreased with age, probably due to an increase in its arousal. This non-intrusive methodology allows the description and analysis of acoustic signal parameters and acoustic exploratory behaviour of a dolphin calf within its social group.