Association patterns and pod cohesion in northern resident killer whales (Orcinus orca)

Understanding the social structure of a killer whale community may give insight into the short-term factors that determine pod-cohesion and pod-splitting. Social patterns within British Columbia's northern resident killer whale community were analyzed using a 20-year long photographic database. Females were found to associate primarily with their mothers when young, and with their own offspring later in life. They showed a surprising lack of contact with other females in their pod, and were photographed more often with females of other pods. Males seemed to be the preferred associates of all pod members, especially other males. Upon reaching age 21, males showed an explosion in social contacts of all sorts, especially with their extended kin. The results suggest that it is male social bonds that give cohesion to killer whale pods, binding two or more related female-offspring units. Female associations are mainly between mothers and their offspring, and their associations with females of other pods may give some cohesion to the community as a whole. These patterns lead to the prediction that without an adult male and the possibility of male-male bonds between mother-offspring units, a pod is likely to split after the death of the common mother. This prediction is consistent with observed cases of pod-splitting.Science, Faculty ofZoology, Department ofGraduat