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Alliance formation by male Indo-Pacific humpback dolphins of north-western Australia

Allen, S., Cagnazzi, D., Krützen, M., Bejder, L. and Parra, G. (2011) Alliance formation by male Indo-Pacific humpback dolphins of north-western Australia. In: 48th Annual Conference of the Australian Marine Science Association, 3 - 7 July, Fremantle, Western Australia.


Indo-Pacific humpback dolphins (Sousa chinensis – ‘Sousa’ hereafter) are found in shallow, near-shore waters of the northern Australian coastline, reefs and islands. Their social structure has been described only superficially, but appears characterized by a fission-fusion grouping pattern, similar to that of several other coastal delphinids. Sexual segregation has not been reported. We conducted boat-based photo-identification, biopsy sampling and behavioural surveys of tropical delphinids between Coral Bay and Broome from April to July, 2010. Here, we provide preliminary evidence that male Sousa in north-western Australia form allied pairs. Firstly, there was a high proportion of large, scarred pairs found in close proximity and engaged in coordinated behaviours that we tentatively assigned as males based on physical appearance. These preliminary classifications were later proven to be correct by genetic sexing. Secondly, we documented both aggressive and affiliative display behaviours by individuals within putatively allied pairs toward other conspecifics. Thirdly, we recorded instances of object-carrying (a possible socio-sexual display) by individuals within pairs of adult male Sousa around adult female Sousa, as well synchronous behaviour between suspected male allies in social settings. These findings suggest an as yet unrecognized level of social complexity in this species. They also highlight what little is known of the social ecology of two tropical delphinid species (Indo-Pacific humpback and Australian snubfin dolphins, Orcaella heinsohni) that inhabit the rapidly developing coastline of north-western Australia.

Item Type: Conference Item
Murdoch Affiliation: Centre for Fish and Fisheries Research
School of Biological Sciences and Biotechnology
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