Social Strategies of a Consummate Marine Predator: Mammal-Hunting Killer Whales

Abstract

Wolves of the Sea is a commonly used moniker for mammal-hunting killer whales, but they are more than that with unique and blended characteristics of mammalian social carnivores. These marine mammal hunters are not archetypical predators. On current evidence, mammal-hunting killer whales do not show territoriality or defense of kills but may exhibit dominance hierarchy to reduce mating competition. But like most social mammalian carnivores, the social unit is fluid and female dominated. Mammal-hunting killer whales also show parental care, social bonding, culture, and social learning. The exceptionality of mammal-hunting killer whales is their embrace of a community of related and unrelated killer whales that share kill and do not compete for the same resources. Although the evolution of mammal-hunting killer whale societies is an area requiring research, there are ecological factors that may explain the social tolerance. For instance, adult killer whales have no natural predators and dominate the world’s oceans feasting on diverse and abundant prey. Their hunting effectiveness, marine mammal diet, and high prey accessibility may be enough to meet energy needs and prevent the need for resource defense. Further, the ability of mammal-hunting killer whales to traverse huge distances and maintain extensive home ranges allows them to be flexible in their dietary patterns—going where the food is plentiful. Killer whales in shared habitats have developed remarkably different hunting behaviors that are adapted to prey type and ecological factors. Hunting group sizes are variable and consistent for pinniped prey, especially pups and juveniles. However, with exceptions, there is insufficient evidence available to correlate group sizes by prey type or hunting success. Despite a wealth of data from certain regions, we remain unaware of the strength of social associations and competition within an apparent expansive social network. We also lack knowledge about their hunting success, group size variation throughout the hunt, and costs/benefits of participating group and non-group killer whale individuals. Mammal-hunting killer whales seem engineered to hunt. They rarely switch off from foraging mode and seek to intimidate, harass, and hunt a variety of prey wherever they occur. Killer whale prey are not naïve and unresponsive. Most killer whale prey follow antipredator strategies and tactics that help to evade killer whale attacks or make it challenging for the predators to succeed. In this predator-prey behavioral game, killer whale hunting strategies are still far from understood. And while there is increasing evidence of sublethal effects from killer whales on prey behavior, our knowledge is limited to a few systems with no substantive analyses of killer whale ecosystem roles in human-dominated seascapes. Finally, there is a growing realization that killer whale communities, beyond the immediate social group, may be conduits for information transfer and that within social units, vertical and horizontal transmission of various hunting behaviors is important for succession and survival. Conservation approaches must consider the preservation of killer whale social units as human perturbations and climate change alter the marine ecosystems in unprecedented ways.