Macrogeographic variations in the structure and repertoire of whistles from four geographically separated bottlenose dolphin (Tursiops aduncus) populations from the east and west coasts of Australia were investigated. Microgeographic variations were examined from two adjacent social groups from the same east coast population. Whistles were divided into five different tonal classes; sine, rise, down-sweep, flat and concave. The acoustic parameters of whistles; start, end, low, high and carrier frequencies and the number of inflection points and harmonics were measured and compared. These features were used to identify and define distinct whistle types. Differences in acoustic parameters of whistles between populations varied with the tonal class and the acoustic parameter being tested and were likely to be driven by localized environmental conditions. There were few differences in the acoustic parameters of whistles between social groups which was likely a result of vocal learning and mimicry from intermixing of individuals. There were small percentages of distinct whistle types that were shared between the both intermixing social groups and geographically separated populations, however, the majority of the whistle repertoires were unique. The development of the unique whistle repertoires may be primarily driven by the complex social organization of the bottlenose dolphin.

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo-Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free-ranging populations was extracted and sorted into whistle types of similar shape using automated categorization. A signature whistle identification method based on the temporal patterns in signature whistle sequences of T. truncatus was used to identify signature whistle types (SWTs). We then compared the degree of variability in SWTs for several whistle parameters to determine which parameters are likely to encode identity information. Additional recordings from two temporarily isolated T. aduncus made during natural entrapment events in 2008 and 2009 were analyzed for the occurrence of SWTs. All populations were found to produce SWTs; 34 SWTs were identified from recordings of free-ranging T. aduncus and one SWT was prevalent in each recording of the two temporarily isolated individuals. Of the parameters considered, mean frequency and maximum frequency were the least variable and therefore most likely to reflect identity information encoded in frequency modulation patterns. Our results suggest that signature whistles are commonly used by T. aduncus.

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.

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