Orcas, also called killer whales, are the largest members of the dolphin family. Adult males reach 8-9 meters (26-30 feet) and can weigh 6,000 kg (13,000 lbs), while females are smaller at around 6-7 meters (20-23 feet) and 3,000-4,000 kg (6,600-8,800 lbs). A male's dorsal fin can stand 1.8 meters (6 feet) tall, the tallest of any marine mammal.
Their striking black-and-white pattern is a form of camouflage called countershading. The white eye patch, white chin and belly, and the grey saddle patch behind the dorsal fin are unique enough that researchers use them to identify individuals.
Orcas have 40-56 large, cone-shaped teeth, up to 10 cm (4 inches) long, built for gripping rather than chewing. Females can live 50-90 years and males around 30-60 years. Calves are born after a pregnancy of about 17 months and nurse for a year or more.
Orcas are found in every ocean on Earth, from the tropics to the pack ice at both poles, which makes them the most widely distributed mammal after humans. They are most common in cold, productive coastal waters such as the Pacific Northwest, Norway, Iceland, Antarctica and the sub-Antarctic islands.
Different populations, known as ecotypes, keep to their own ranges and ways of life, and rarely mix even where their territories overlap.
Orcas are apex predators with no natural enemies. What they eat depends on their ecotype: resident populations in the North Pacific feed almost entirely on fish such as salmon, while transient (Bigg's) orcas hunt seals, sea lions, porpoises and even large whales. Other populations specialise in herring, sharks, rays, penguins or squid.
An adult eats roughly 50-150 kg (110-330 lbs) of food a day.
Orcas live in tight family groups called pods, led by the oldest female. Sons and daughters often stay with their mother for life. Each pod has its own set of calls, a dialect passed from generation to generation.
They are famous for cooperative hunting: working together to wash seals off ice floes, herding herring into tight balls, or beaching themselves on purpose to grab sea lions in the surf. Hunting skills are taught to the young over many years.
The orca, Orcinus orca, is the only living species in its genus and belongs to the oceanic dolphin family Delphinidae. Scientists recognise several distinct ecotypes, differing in size, markings, diet and calls, and some of these may eventually be classified as separate species.
The International Union for Conservation of Nature (IUCN) lists the orca as Data Deficient, because the global population is not well counted and some local populations are doing far worse than others. The Southern Resident orcas of Washington and British Columbia number fewer than 80 animals and are listed as endangered in the United States and Canada.
The main threats are a shortage of prey such as Chinook salmon, chemical pollution that builds up in their blubber, underwater noise from ships, and the lasting effects of past captures for marine parks.
