Bioacoustics of Orcinus orca

Activity patterns. Foraging and traveling are the most common behaviorsin all studied populations of Killer Whales. Resident Killer Whales spend a much higher proportion of their time foraging and traveling (90-95%) than do transient Killer Whales (60-70%) that spend more time socializing and resting. Herring-specialist populations of Killer Whales off northern Norway have an activity budget very similar to that of resident Killer Whales in the north-eastern Pacific Ocean, suggesting that the proportion of time spent traveling and foraging depends heavily on preferred prey type. Resident Killer Whales have seasonal inshore—offshore movements associated with migrating salmon and forage in bouts of 2-3 hours. Pods move in a consistent direction at a mean swimming speed of ¢.6 km/h, with individuals widely spread out. Caught prey may be shared among small subgroups or among mothers and offspring. Resident Killer Whales tend to be vocally quiet while foraging, repeating discrete calls drawn from an average repertoire of twelve call types per pod. Diving patterns of transient Killer Whales vary throughout the day. Generally, deep dives are more frequent during the day and shallow dives are of longer duration during the night. When traveling, Killer Whales will orient themselves in a line abreast and move in a single direction at a fast pace of up to 20 km/h. Dives may be synchronized. When resting, Killer Whales will also swim in a line abreast but at slower speeds and spaced more tightly together. Vocalization is minimal, and dives will be synchronized and regular, with long dives of 2-5 minutes separated by a series of 3—4 short dives. Resting groups may also be stationary. The Killer Whale is known to be aerially active; breaching, spy hopping, and fluke and flipper slapping are common. Resident Killer Whales in the north-eastern Pacific Ocean regularly visit kelp beds and shallow pebble beaches, where individuals will intentionally rub their bodies through kelp fronds or along smooth pebbles on the sea floor. This behavior seems to be social and apparently pleasurable.

Food and Feeding. The Killer Whale is an apex predator. Globally, it is a generalist with a diverse diet. There are over 140 species of documented prey including a wide variety of small and large fish, cephalopods, marine mammals, seabirds, and marine turtles. The Killer Whale is the only cetacean species known to have populations that specialize on mammal prey. Over 50 different species of mammals have been documented as prey including cetaceans, pinnipeds, sirenians, mustelids, and occasionally even ungulates and ursids. On a local scale, populations of Killer Whales are often distinguished by dietary specializations. For example, resident Killer Whales in the north-western coast of North America feed almost exclusively on salmon (Oncorhynchus spp.) and are not known to feed on endothermic animals. They appearto prefer the largest and most fat-rich species (Chinook salmon, O. tshawytscha, and Cohosalmon, O. kisutch), despite smaller species such as sockeye salmon (0. nerka) occurring in greater abundance. Transient Killer Whales in the same area, by contrast, hunt marine mammals and do not consume fish. Preferred prey include Harbor Seals (Phoca vitulina), Harbor Porpoises ( Phocoena phocoena ), and Dall’s Porpoises ( Phocoenoides dalli), and they will also eat Steller Sea Lions (Eumetopiasjubatus), California Sea Lions (Zalophus californianus), Northern Elephant Seals (Mirounga angustirostris), Pacific White-sided Dolphins ( Lagenorhynchus obliquidens ), and Common Minke Whales (Balaenoptera acutorostrata). Transient Killer Whales off the coast of California specialize on Gray Whales (Eschrichtius robustus) and will attack young that are accompanying their mothers northward on their first migration. Dietary preference of offshore Killer Whales is currently poorly known but appears to include more offshore fish species such as Pacific halibut (Hippoglossus stenolepis) and various carcharinid sharks. Resident, transient, and offshore killer whales, although partially sympatric in their distributions, do not appearto associate with each other and are unambiguously distinct in mtDNA and nDNA composition. Given their dietary specializations, this genetic divergenceis likely the result of foraging strategies being socially passed across generations. This would have eventually given rise to divergent enough skill-sets so as to underlie mutually exclusive lifestyles, making for an intriguing and rare case where ecological divergence is likely driving incipient sympatric speciation. Populations of Killer Whales that inhabit Norwegian fjords specialize on herring ( Clupea spp. ) and behaviorally resemble resident Killer Whales in the north-eastern Pacific Ocean. The Antarctic type A Killer Whale specializes on the Antarctic Minke Whale (B. bonaerensis), and type B populations in the vicinity of New Zealand may specialize on sharks and other elasmobranchs. The type C Killer Whale feeds primarily on Antarctic fish species, and some populations of type D Killer Whale are thought to prefer Patagonian toothfish (Dissostichus eleginoides). In the Canadian Arctic, Killer Whales most commonly prey on the Beluga (Delphinapterusleucas) , the Narwhal ( Monodon monoceros), and the Bowhead Whale (Balaena mysticetus). In multiple populations, dietary specialization has led to development of unique foraging strategies. For example, Norwegian populations of Killer Whales use a strategy called “carousel feeding,” during which a school ofherring is herded into a tight ball near the water’s surface. Individual whales then stun and pick at prey around edges of the ball. Killer Whales in the Strait of Gibraltar feed on Atlantic bluefin tuna ( Thunnus thynnus) by chasing schools for ¢.30 minutes at high speed until tuna are exhausted. Transient Killer Whales usually hunt in small groups and are more acoustically quiet than resident Killer Whales, likely to keep from alerting their mammalian prey. Killing seals and sea lions usually involves repeated ramming, slapping them with flukes, or even leaping on them. After prey is stunned,it is dragged underwater and drowned. The killed animal is then shared among the group. Killer Whales may herd large groups of dolphins or porpoises into confined bays where they can be easily killed after being trapped (a strategy that is disturbingly reminiscent of human dolphin drives). Larger groups of transient Killer Whales are required to successfully attack mysticetes and the Sperm Whale (Physeter macrocephalus). The group will coordinate itself so that some individuals grasp flippers and tail flukes of prey to impede movement while others gash at the blowhole area to impair breathing. Blubber,lips, and tongue are usually the only parts of the killed whale that are consumed. Groups of type B Killer Whale in Antarctica have learned how to coordinate forceful water waves to wash over and tilt ice floes to dislodge Weddell Seals (Leptonychotes weddelliz) resting on them. When this wave-washing technique fails, one or two Killer Whales may even lift the ice floe with their heads to flip it over or break it. Killer Whales off Patagonia, Argentina, have developed a strategy for hunting young Southern Elephant Seals (Mirounga leonina) and South American Sea Lions (Otaria byronia) that involves intentionally stranding themselves temporarily on the sloping beaches. Killer Whales around the Crozet Islands use a similar method, and in this region, there is compelling evidence to suggest that adults actively teach this strategy to their offspring.