Whistle vocalizations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) inhabiting the south-west Indian Ocean

Populations of Indo-Pacific bottlenose dolphin (Tursiops aduncus) are distributed along coastal regions of the south-west Indian Ocean (SWIO), from South Africa to Kenya. An account of whistles from wild T. aduncus inhabiting the SWIO is provided here. Recordings were made at Plettenberg Bay (South Africa) and Zanzibar Island (Tanzania) and the frequency trace of whistle contours (n = 1677) was extracted. Multiple parameters were measured from each whistle and compared between regions and encounters. Regional variation was significant in all parameters assessed except for start and middle frequency (frequency at half the duration). Whistles from Zanzibar Island ended on average 4 kHz higher than those from Plettenberg Bay, and had a steeper frequency gradient. However, mean frequencies differed by <1 kHz and population averages for the adopted frequency distribution showed similar patterns, with a peak between 5 and 7 kHz. Whistle parameters were strongly influenced by recording encounter, likely reflecting the presence of different individuals, group compositions and behavioral contexts during recording occasions. Comparisons within the genus showed that T. aduncus from the SWIO have amongst the lowest start and minimum frequency of whistles within Tursiops.