Whistle emissions of Indo-Pacific bottlenose dolphins (Tursiops aduncus) differ with group composition and surface behaviors

The intricate and highly developed acoustic communication system of bottlenose dolphins reflects the complexities of their social organization. Indo-Pacific bottlenose dolphins (Tursiops aduncus) produce numerous types of acoustic emissions, including a diverse repertoire of whistles used for communicative purposes. The influence of group composition on whistle production and the function of different whistles produced by dolphins in wild contexts are relatively unknown. Recordings of acoustic emissions and behavior of dolphins were made concurrently during vessel-based surveys along the coast of northern New South Wales, Australia. Whistles were divided into five tonal classes (sine, rise, down-sweep, flat, and concave) and categorized into distinct whistle types. It is shown that while whistle repetition rate and whistle diversity was influenced by group composition, it is not influenced by behavior. Noncalf groups produced a significantly higher whistle repetition rate and whistle diversity than calf groups. In contrast, the types of whistles produced were related to the behavior in which the dolphins were engaged in: some tonal classes and distinct whistle types were related to different behavior states. Findings suggested that some whistle types may be used to communicate specific information on the behavioral context of the individuals involved.