Patterns of whistles emitted by wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) during a provisioning program

To facilitate and coordinate the complexities of fission-fusion societies, Indo-Pacific bottlenose dolphins (Tursiops aduncus) have developed a multilayered acoustic communication system to effectively transmit signals in the marine environment. Among the many acoustic emissions produced by dolphins, whistles are thought to play a major communicative role. Little is understood about the functions of the diverse whistle repertoire of wild bottlenose dolphins and the influence human activities can have on these sounds. This study provides a detailed investigation into the use and diversity of whistles by a group of eight wild bottlenose dolphins that participate in a provisioning program at Tangalooma, Moreton Island, Australia. Acoustic recordings and concurrent behavioural observations were made during evening feeding sessions. Behaviours were divided into three activities: (1) milling, (2) scanning/foraging (excluding human provisioning), and (3) socialising. Pod separation occasions were also examined. Whistles were classified as either stereotyped or nonstereotyped and divided into five tonal classes based on the shape of the fundamental frequency: (1) sine, (2) up-sweep, (3) down-sweep, (4) flat, and (5) concave. Whistles were then catalogued into distinct whistles types. From 943 min of recordings, 5,682 whistles were analyzed that then were catalogued into 68 distinct whistle types of which 18 were stereotyped and 50 were nonstereotyped. The repetition rate (x = 1.12 whistles per min per dolphin [w/m/d]; SD = 0.61) and diversity of whistles varied between feeding sessions but were not related to the number of dolphins. Distinct whistle types were divided into common or uncommon categories to facilitate correspondence analysis to examine associations between whistles and behaviour activities. Results showed that around 38% of common whistles and 84% of uncommon whistles were closely associated with behaviour activities, particularly socialising and scanning/foraging. Sine whistles were the only tonal class associated with pod separation. This study provides further evidence of the communicative functions of whistles across the repertoire of wild bottlenose dolphins.