  Techniques recently developed for the analysis of human social networks are
applied to the social network of bottlenose dolphins living in Doubtful Sound,
New Zealand. We identify communities and subcommunities within the dolphin
population and present evidence that sex- and age-related homophily play a role
in the formation of clusters of preferred companionship. We also identify
brokers who act as links between subcommunities and who appear to be crucial to
the social cohesion of the population as a whole. The network is found to be
similar to human social networks in some respects but different in some others
such as the level of assortative mixing by degree within the population. This
difference elucidates some of the means by which the network formed and
evolves.
