Killer Whale (Orcinus orca)
Food and Foraging Strategies
Image courtesy of SeaWorld
Predators:
Killer
whales are top predators. They are the kings of the sea, with no
natural enemies other than humans (Hammers, 2003).
Image courtesy of Webshots
Food:
Known as the “Wolves of the sea”, orcas are fearsome predators. They have the most varied diet of all cetaceans and can tackle prey of all shapes and sizes. Killer whales have coordinated hunting strategies. They work as a team and not as individual units within the pod. This shows their intelligence and cunning (Cetacea, 2004). They are highly adaptable and cooperative predators (Guinet, 1991) with powerful jaws that are equipped with 10 to 14 pairs of large, rather blunt conical teeth which interlock when the animal closes its jaw (Norris, K., 1958).
Orcas feed on a variety of prey including several kinds of fish, cephalopods, pinnipeds, cetaceans, and birds (Similä, 1996). Because of their wide range of prey items, killer whales have been considered by some to be generalized, opportunistic feeders; however, individual populations of killer whales may actually specialize on preferred prey for their given area (Heimlich-Boran, 1988).
In a study of diet preferences of killer whales, Similä (1996) found that there may be variation within the same geographical area. In the northeast Atlantic waters, the occurrence of killer whales is associated with the presence of herring, salmon and mackerel. Other types of prey are cod, squid, seals, and bottlenose whales. Marine birds, however, are not an important part of the diet of killer whales.
Resident and transient pods differ in their diets (Animal Planet 2002). All of the prey seen taken by transients were marine mammals, including harbor seals, Dall’s porpoises, Stellar sea lions, harbor porpoises, humpback, minke, and gray whales, and river and sea otters. (Ford, 1998; Saulitis, 2000). Resident killer whales, however, appeared to prey principally on salmon for at least half the year (Saulitis, 2000). Residents were seen frequently to interact in non-predatory ways with Stellar sea lions and Dall’s porpoises, while transients were not (Saulitis, 2000).
Foraging Strategies:
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The specialist foraging of killer whales is an extreme example, where some killer whales consume marine mammals nearly exclusively, and others concentrate on fish prey (Hoelzel, 1994). Local populations, living sometimes in sympatry, appear to specialize in hunting certain types of fish or marine mammals (Guinet, 1991) and following seasonal movements of their preferred prey (Similä, 1996).
The cooperative social organization and system of communal rearing that characterizes many of the larger carnivores, such as the killer whale, is in part based on cooperative group endeavors that increase foraging efficiency. This involves highly coordinated strategies of pack hunting or group foraging, which may include cooperative defense of carrion caches or unpredictable food supplies. (Riedman, 1982)
Groups of killer whales hunt in a coordinated fashion (Heimlich-Boran, 1988) which normally occurs during dives of less than 100m. The members of the pod cooperate to keep the prey at or near the surface (Cetacea, 2004). This behavior is dependent on a high degree of communication and coordination within the group and is an important means to increase feeding efficiency on either individual large marine mammals or large schools of small fish (Heimlich-Boran, 1988). The whales appear to search for food cooperatively by foraging in spread out subgroups in line-abreast formations. This serves to increase their search area (Heimlich-Boran, 1988). Killer whales are also highly vocal while foraging, emitting both social signals and echolocation trains (Ford, 1998)
Both transient and resident groups exhibit regular patterns of movement that are undoubtedly mediated by memories of locations that have provided previous feeding success (Heimlich-Boran, 1988). Many of the distinctions between residents and transients may be based on learned differences. Because foraging strategies are learned traditions that have developed over many generations by imitation (Ford, 1998), it appears to be an important part of the development of feeding strategies of adult killer whales, apparently training young in the capture of pinniped prey (Heimlich-Boran, 1988). Killing a large whale is too dangerous for the calf, but as a spectator, it picks up lethal techniques like ramming, drowning, and biting the prey (Hammers, 2003).
In open water foraging, when prey is detected, often a coordinated chase involving all the whales in the group ensues, and prey is shared among group members (Saulitis, 2000). All porpoise kills that are observed occur during open-water foraging (Saulitis, 2000). When foraging nearshore, individuals typically separate from one another, traveling along different parts of the shoreline (Saulitis, 2000). When foraging in narrow channels and straits, females and young usually swim 50-100m of the shoreline giving them the ability to corral and capture prey while males forage farther from shore (Ford, 1998).
Because transients are specialized hunters of marine mammals and seabirds, they depend on a foraging tactic involving stealth (Ford, 1998), which is attained because of the greater fluidity of the social structure (Ford, 1998). Transients spend more time foraging and less time resting than residents. Both spend majority of time traveling and foraging (Saulitis, 2000).
Image courtesy of America Zoo