FORAGING BEHAVIOR AND SOCIAL GROUP-DYNAMICS IN PUGET-SOUND KILLER WHALES

Social and foraging behaviour was investigated in a population of 82 killer whales, Orcinus orca, seasonally resident in the straits of Washington State and British Columbia. Killer whales in this population travel in stable pods and temporarily dissociate into subgroups. Associations in subgroups were determined by photographing individual whales. The relative geographical positions of subgroups were determined by compass triangulation on landmarks. These data were used to determine correlations between individual associations, habitat use and behaviour. Behaviour indicative of pursuing fish prey at the surface (termed fast non-directional) correlated with the whales slowing down, travelling in smaller subgroups, and decreasing the distance between subgroups. This behaviour was not correlated with bottom topography, specific quadrats within the study areas, or the convergence or subgroups (which could be interpreted as group herding of prey). These data suggest that these killer whales way benefit from cooperative food searching, but not necessarily from cooperative food capture. Adult males, which are thought to remain within their natal pods, were most likely to travel alone and to exhibit fast non-directional behaviour when alone. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.