Introduction to Killer Whale Facts
Among the members of the dolphin family, the killer whale (Orcinus orca) is the largest of all. The killer whale is easily distinguished by its large size and remarkable coloration: jet black on top and pure white below, with a white patch above each eye, another going along each flank, and a varied “saddle patch” directly behind the dorsal fin. Even though this cetacean is a strong carnivore, there is no evidence of it killing humans in the wild. Dozens of killer whales have been held in captivity and trained as entertainers, a practice that has become more unacceptable in the twenty-first century.
Physical Characteristics of Killer Whales
Males can grow to be over 10 meters (32.8 feet) long and weigh around 9,800 kg (approximately 10 metric tons or 11 short [U.S.] tons), while females grow to be about 8.5 meters (27.8 feet) long and weigh much less than males. Males also have proportionally longer appendages, with flippers up to 2 meters (6.6 feet) long—about 20% of the body length—and over 1 meter (3.3 feet) wide. Female flipper length ranges from 11 to 13 percent of body length.
The dorsal fin of older males is very tall (up to 1.8 meters [5.9 feet]) and straight; females and young males have a dorsal fin that is about half that height and sickle-shaped (falcate). The skull is at least a meter long and has the largest brain of any dolphin, weighing an average of 5.6 kg (12.3 pounds). The muscles that close the mouth are massive, and the jaws include a set of almost 40 interlocking curved teeth. The majority of the teeth are huge, measuring approximately 10 cm (4 inches) long and 4 cm (1.6 inches) wide.
Geographical Distribution and Habitat
The killer whale has an uneven distribution throughout the oceans, from the northern ice caps to the Equator, where huge prey like tuna, salmon, and seals are plentiful. Other food sources include squids, sea lions, penguins, whales, and porpoises. In the North Pacific, varied populations exist along the Alaskan coast, in British Columbia and Washington’s Intracoastal waterways, and off the coast of Baja California.
In the North Atlantic, they can be found from Newfoundland and Labrador to Iceland, Norway, and the British Isles. In the Southern Hemisphere, they can be seen off the shores of Argentina, South Africa, New Zealand, and the Galapagos Islands.
Social Structure and Communication
They live in small groups, known as pods, with less than 40 animals each. Resident pods and transient pods have been analyzed in the populations of British Columbia and Washington. Sound production and nutrition vary amongst them, with resident pods (those that live in Puget Sound and neighboring coastal waters) eating fish (mainly salmon) and transients (those that roam greater areas of coastal waters) eating other cetaceans, gulls, and seals. Killer whales use echolocation to feed and communicate.
Reproductive Traits and Menopause
Killer whales, known for their intelligence, are one of the few nonhuman animals that can recognize themselves in a mirror. They, along with humans (Homo sapiens), short-finned pilot whales (Globicephala macrorhynchus), false killer whales (Pseudorca crassidens), belugas (Delphinapterus leucas), and narwhals (Monodon monoceros), are among the few species that go through menopause.
The conditions under which menopause evolved in killer whales are unknown, however, it may have occurred in reaction to increases in the mortality of children from earlier generations during periods when mothers and daughters mated simultaneously.
Some experts believe that younger females in the pod are more concerned with the success of their children and may be more competitive for food supplies than older females (see competition). Killer whale pods are extended families with matriarchal hierarchies (see also dominant hierarchy). The older females, who are more concerned with the success of the pod as a whole, may be more ready to share food with the rest of the pod, limiting the amount of food available for their children.
The evolutionary history of the genus Orcinus is limited. The earliest known killer whale fossil is O. citonensis from Italy’s Pliocene Epoch (5.3 million to 2.6 million years ago). This little mammal was around 4 meters (13.1 feet) long and had 14 teeth, similar to a common dolphin. This means that the progenitors of the modern killer whale separated from other cetaceans during the Miocene Epoch (23 million to 5.3 million years ago); the majority of dolphin evolution occurred near the beginning of this epoch.
Taxonomy and Classification
Although the killer whale’s taxonomy is unambiguous at the genus and family levels (Delphinidae), its affiliations with other toothed whales (suborder Odontoceti) remain uncertain. The false killer whale (Pseudorca crassidens), pygmy killer whale (Feresa attenuata), Risso’s dolphin (Grampus griseus), and pilot whales (Globicephala species) are regarded to be relatives of the killer whale.
Killer whales are often classified into one of two Delphinidae subfamilies: Orcininae (killer whales and kin) and Globicephalinae (pilot whales and kin). The killer whale has been given over 20 different species names, but only O. orca is now widely accepted. Killer whales were once known as grampuses, but the term is now a synonym for Risso’s dolphin.
Evidence of Speciation in Killer Whale
Evidence suggests that O. orca is in the process of splitting into two species in the North Atlantic. Based on genetic research and examinations of body size and tooth wear, scientists believe that two distinct populations with distinct feeding habits and morphological traits have evolved. One population, distinguished by relatively small individuals with a maximum length of 6.6 meters (21.7 feet) and substantial tooth wear, preys on fish, seals, and other mammals.
In contrast, the other group, which is distinguished by larger individuals that can grow to 8.5 meters (27.9 feet) in length and have relatively minimal tooth wear, is considered to prey mainly on whales and other dolphins.
There is evidence that killer whale diversification is also taking place in the North Pacific, where there could be up to three genetically distinct groups with radically different dispersal patterns, calls, social structures, and diets. These groups are called “residents” (fish-eating populations mainly based in the Sea of Okhotsk and the western part of the Bering Sea), “transients” (mammal-eating populations inhabiting the Gulf of Alaska, the eastern Aleutian Islands, and the eastern Bering Sea), and “offshores” (killer whales found along the west coast of North America between the Queen Charlotte Islands and California).