Drivers of vocal production in wild bottlenose dolphins (Tursiops truncatus): functional differences between whistle types.
Supervisor: Bruno Díaz López (Bottlenose Dolphin Res Institute)
Acoustic communication plays a fundamental role in the animal world, facilitating contexts such as courtship, mating, feeding and parenting. While vocal communication is fairly widespread in animals, only few socially structured groups exhibit high cognitive skills and complex communication elements, and in the relatively novel field of bioacoustics there is still a paucity of information in a number of species and environments, such as the ocean. The bottlenose dolphin is a highly social cetacean that has developed an advanced acoustic communication system which includes echolocation and social sounds, such as whistles, making it a great model organism to study vocal sound production. The aim of this study is to elucidate some of the factors that influence the production of whistles (signature and variant) in different resident population of bottlenose dolphins (Tursiops truncatus) using data collected over the course of two long-term studies. More than 189 hours of acoustic recordings were collected between 2005 and 2020, along with data about group behaviour and social structure, providing an amount of natural variability that is rarely available. From this dataset, 1119 1-minute samples of 373 distinct groups of dolphins were randomly selected in order to reduce temporal correlation and recording duration bias. The presence and number of whistles in each minute were recorded by visually and aurally inspecting each sample using spectrograms. Four response variables (overall presence of whistles, rate of whistles per minute, presence of signature whistles and presence of variant whistles) were then modelled using Generalized Linear Mixed Models (GLMMs). The main drivers of whistle production overall were found to be behaviour and group size. Results also show, possibly for the first time, that different whistle types may have functional differences. This study not only fills a knowledge gap in the field of dolphin communication but also provides information that is applicable to other highly social species with complex acoustic communication systems.

Key Words: Animal communication, bottlenose dolphin, sound production, whistles, signature whistles, variant whistles.