Vocalizations Produced by Bottlenose Dolphins (Tursiops truncatus) during Mouth Actions in Aggressive and Non-aggressive Contexts

Abstract

Dolphins exchange information with conspecifics using different types of vocalizations that are often associated with specific behaviors. The present study used simultaneous acoustic and video recordings of captive bottlenose dolphins (Tursiops truncatus) in Honduras to describe potential correlations between the type of mouthing behavior (open mouth, mouthing, bite) and associated vocalizations (whistle, whistle-squawk, chirp, moan, burst-pulse ‘A’, burst-pulse ‘B’, clicks). Literature on sound-behavior relationships among odontocetes with the noted infrequent systematic analyses of mouth actions highlights the need for this investigation. The influence of aggression on vocalization use was also addressed. From this observational study a series of general expectations on the interaction of sound, mouth action, and aggressive context are presented. Mouth actions are associated with vocalizations more often than not, and results suggest an overall flexible association of vocalizations during mouth actions, with the production of various sounds altered during aggressive contexts. There is an apparent distinction of frequency-modulated sounds with mouthing, suggesting that frequency parameters are an important characteristic of information exchange during mouth actions, and further that mouth actions are individually distinct behaviors. A dichotomy of burst pulse sounds in association with aggressive and non-aggressive contexts also introduces the need to analyze pulsed sounds according to inter-pulse interval. This paper proposes that there may be an interactive function to the use of vocalizations during mouth actions that is not yet understood.