Rich Connor: University of Massachusetts Dartmouth

For over 25 years we have documented a multi-level alliance structure among male bottlenose dolphins in Shark Bay, Western Australia. Males cooperate in pairs and trios, ‘1st-order alliances,’ to form temporary consortships with individual females. First-order alliance partners are drawn from a male’s second-order alliance. Second-order alliances have 4-14 males and may be stable for over two decades, but occasionally lose or take in new members. First-order alliances vary in stability but this variation is not strongly related to 2nd order alliance size. Members of 2nd order alliances engage with conflicts with other groups over females, sometimes in the company of other 2nd order alliances they associate with, suggesting a 3rd alliance level. The male alliances and individual females live in an open social network where both sexes maintain their mother’s natal range as part of their adult home range. The study area can be divided into a subdivided area characterized by shallow offshore flats bisected by deeper channels and an open habitat. Trios predominate in the open habitat while pairs are common in the subdivided habitat. Further, the largest 2nd order alliances (>9) use the open habitat at least part of the year. The combination of 120 males with known alliance affiliations combined with recent technological advances presents an exciting future for studies on the development, communication, genetics and ecology of alliance formation.