Killer Whales: Behavior, Social Organization, and Ecology of the Oceans’ Apex Predators

Abstract

The killer whale—the largest of the dolphins and the top marine predator––has a cosmopolitan distribution throughout the world’s oceans. Although globally it could be considered a generalist predator with a diverse diet, it is deeply divided into ecotypes, many of which have distinct foraging strategies involving only a narrow range of prey species. These ecotypes, which often exist in sympatry, are believed to arise from culturally driven dietary specializations that develop within matrilineal social groups and are transmitted among matriline members and across generations by social learning. Specializations are maintained by behavioral conformity and social insularity of lineages, which result in reproductive isolation and, ultimately, genetic divergence of ecotypes. Ecotypes have distinct patterns of seasonal distribution, group size, social organization, foraging behavior, and acoustic activity that are related to the type of prey being sought. Sophisticated cooperative foraging tactics have evolved in some ecotypes, and prey sharing within matrilineal social groups is common. Remarkable behavioral and demographic attributes have been documented in one well-studied ecotype, including lifelong natal philopatry without dispersal of either sex from the social group, vocal dialects that encode genealogical relatedness within lineages, and multi-decade long post-reproductive periods of females. Cultural traditions of killer whales, including foraging specializations, can be deeply rooted and resistant to change, which may limit the ability of ecotypes to adapt to sudden environmental variability.