Social affiliations within sperm whale (Physeter macrocephalus) groups

We examined patterns of affiliation within groups of sperm whales (Physeter macrocephalus), particularly concentrating on how short-term spatio-tempor al associations reflect long-term relationships. Female and immature sperm whales live in stable, and partially matrilineal, social units. Two or more social units may move together for periods of several days, forming a cohe sive group of about 20 animals. We observed that sperm whales in the easter n tropical Pacific quite consistently associated with members of their own social unit more than they did with other animals in their group with whom they did not share a longterm relationship. There was little evidence for p referred, or avoided, affiliations within social units, except in two large and relatively unstable units. In two well-studied groups, individuals did not show consistently favoured positions in the foraging rank relative to other members of their social unit. These results indicate the importance o f long-term relationships to female and immature sperm whales, but suggest that relationships are quite homogeneous within social units.