Studies of the social ecology of Norwegian killer whales (Orcinus orca)

Abstract

Killer whales along the Norwegian coast have been studied since 1990 with methods based on photo-identification. Preliminary insights of the social characteristics of Norwegian killer whales are presented generally. About 400 killer whales are identified, and 65% of the whales have been resighted. The whales occur in groups of moderate sizes, all containing adult males and breeding females. The groups seem to be social units based at least partly on stable membership. Acoustic analyses revealed both uniqueness and a variable degree of similarity in the vocalization of different groups of whales. The social integrity of groups is further indicated by cooperative feeding on herring, communal care of young, competitive interactions between groups and specialized feeding on marine mammals by one small group of whales. Some adult males have a nomadic occurrence, and, might eventually represent a mating strategy. Ritualized interactions between males appear to be affiliation acts. Large males and female-sized whales do not seem to differentiate in diving behaviour during cooperative feeding due to synchrony in respiration patterns. Norwegian killer whales eresemble the well-studied Canadian killer whales, but there are also indications of some intraspecific variability.