Open social network of dolphins is linked to their relatively low costs of locomotion, not to control either territory or sexual partners
Richard Connor of the University of Massachusetts Dartmouth tracked 120 males in the Shark Bay, Western Australia and found no evidence that dolphins form the groups to control either territory or sexual partners, suggesting their society is unusually open.
The researchers found no evidence that the large and complex social network in Shark Bay, comprising hundreds of bottlenose dolphins, is a closed group defended by males.
They also found no evidence that males defend smaller ranges or groups of females within this network.
Instead, there is extensive overlap in the ranges of alliances and in the females, they consort with.
Combined with earlier work on females, these results lead to the conclusion that Shark Bay bottlenose dolphins live in an open social network with a mosaic of overlapping female and male ranges.
It is unlikely that kinship can offer a complete explanation for the male dolphin network in Shark Bay. Male dolphins do not maintain strong bonds with their mothers and while they form male-male bonds from an early age, the second-order alliances ‘crystallize’ when males are in their teens, after a long juvenile period.
Humans and bottlenose dolphins are the only two species that exhibit nested male alliances within a social network. Some of the profound differences between human and dolphin social organization (e.g. dolphins do not exhibit pair bonds or male parental investment) may relate to the fact that humans are tied to a home base or hearth.