Effect of behaviour on free wild Bottlenose dolphins’ whistles in the Arousa Ria, Galicia

Abstract

Underwater sounds are very important for Bottlenose dolphins (Tursiops truncatus) in order to find food, navigate and mainly to communicate and have been the species of interest for many vocal acoustic studies. From all bottlenose dolphins sound repertoire the most studied communication signals are whistles which have been commonly categorized by their shape. Dolphin communication through sound has a variety of functions in their behaviours. Bottlenose dolphins have been observed producing whistles in many different behavioural situations that allows them to communicate. Although it seems that this whistles can transmit information, it is still unclear which exactly role they have in communication, therefore this study tries to give further information about how dolphins use sound production in different behavioural states. In the present study we analysed if behaviour was influencing whistle production and whistle variability in wild populations of bottlenose dolphins from the Arousa Ria (Galicia). The data used was collected from April to October of 2015. Survey for dolphins were conducted from a research vessel and behavioural information was collected following the predominant activity sample (PAS). Dolphins’ behaviour were categorized in feeding, socializing or travelling states and acoustical recordings were collected with an omni-directional hydrophone (frequency response of 0.02-100 kHz). Whistles were later selected, analysed and categorized by their contour or shape. Our findings showed that group size was not causing any effect on whistle production (Pearson p-value = 0.4942 and r = 0.25) and neither a specific behavioural state was influencing on whistle rates (Anova p-value=0.42). In contrast, whistle variability was found to be associated to a given behaviour (Chi2 p-value 2.84e-26). Our results differ from what found in other areas of the world regarding whistle production and behaviour but are similar regarding whistle variability. However, further long-term research is needed to study bottlenose dolphins in the Arousa Ria.