Resident orcas are the most commonly sighted of the populations, often observed in coastal waters. Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner. While nomadic, their range is much smaller, and they are known to visit certain areas consistently.

The resident orcas' diet consists primarily of fish, including salmon and herring, and they frequent areas where preferred fish are abundant. They are continually on the move, sometimes traveling as much as 100 miles (160 km) in a day, but may be seen in a general area for a month or more. Range for resident orca pods may be as much as 800 miles (1300 km) or as little as 200 miles (320 km).

Resident orcas live in complex and cohesive family groups known as pods. Resident pods are generally larger than the transient and offshore pods, having up to 50 or more members. Several pods occasionally join to form what are referred to as superpods, sometimes numbering in excess of 150 animals. They can also be seen swimming with porpoises, other dolphins and sea lions, which are common prey for transient orcas.

On November 15, 2005, the United States government listed the Southern Resident population of orcas an endangered species under the Endangered Species Act (ESA) due to deterioration of the three pods which spend most of the year in Georgia and Haro Straits, as well as Puget Sound in British Columbia and Washington state.

Fish-eating orcas in the North Pacific have a complex system of social grouping. The basic unit is the matriline, which consists of a single female (the matriarch) and her descendants. The sons and daughters of the matriarch form part of the line, as do the sons and daughters of those daughters (the sons and daughters of the sons join the matriline of their mates) and so on down the family tree. Because females can live for up to ninety years, it is not uncommon for four or even five generations to travel together. These matrilineal groups are highly stable over many years. Individuals will only split off from their matrilineal group for up to a few hours at a time in order to mate or forage. No permanent casting out of an individual from a matriline has ever been recorded. The average matriline size as recorded in northeast Pacific waters is nine animals.

Matrilines form loose aggregations called pods, consisting on average of about 18 animals. Members of a pod all have the same dialect (see the section on vocal behaviour below) and consist of closely related matriline fragments. Unlike matrilines, pods will split apart for days or weeks at a time in order to carry out foraging before joining back together. The largest recorded pod is 49 animals.

The next level of grouping is the clan. A clan consists of those pods which have a similar dialect. Again the relationship between pods appears to be genealogical, consisting of fragments of families with a common heritage on the maternal side. Different clans can occupy the same geographical area; pods from different clans are often recorded traveling together. When resident pods come together to travel as a clan, they greet each other by forming two parallel lines akin to a face-off before mingling with each other.

The final layer of association, perhaps more arbitrary and devised by humans rather than the other very natural divisions, is called the community and is loosely defined as the set of clans that are regularly seen mixing with each other. Communities do not follow discernible familial or vocal patterns.

In the northeast Pacific, three communities of fish-eating orcas have been identified:

The southern community (1 clan, 3 pods, 90 orcas as of 2006)

The northern community (3 clans, 16 pods, 214 orcas as of 2000)

The south Alaskan community (2 clans, 11 pods, 211 orcas as of 2000)

The orca is an apex predator, and the array of species on which orcas prey is extremely diverse. Specific populations show a high degree of specialization on particular prey species. For example, some populations in the Norwegian and Greenland sea specialise in herring and follow that fish's migratory path to the Norwegian coast each autumn. Other populations in the area prey on seals.

The orca is the only cetacean species to regularly prey on other cetaceans. Twenty-two species have been recorded as preyed on, either through an examination of stomach contents, examining scarring on the prey's body, or from observing the orcas' feeding activity. Groups of orcas will even prey on larger cetaceans such as minke whales, gray whales, female and juvenile sperm whales or young blue whales. A group of orcas take a young whale by chasing it and its mother through the sea, wearing them out. Eventually the orcas manage to separate the pair and surround the young whale, preventing it from returning to the sea's surface to breathe. Large whales are typically drowned in this manner. Pods of female sperm whales can sometimes protect themselves against a group of orcas by forming a protective circle around their calves with their flukes facing outwards. This formation allows them to use their powerful flukes to repel the orcas.

There has also been one recorded case of probable orca cannibalism. A study carried out by V. I. Shevchenko in the temperate areas of the South Pacific in 1975 recorded two male orcas whose stomachs contained the remains of other orcas. Of the 30 orcas captured and examined in this survey, 11 had empty stomachs — an unusually high percentage which indicates the orcas were forced to cannibalism through a lack of food.

The diet of orcas shows substantial variation among different populations. Fish-eating populations prey on 30 species of fish, particularly salmon (including Chinook and Coho), herring, and tuna. Basking sharks, oceanic whitetip sharks, and very occasionally even great white sharks are taken for their nutrient-rich livers. Other marine mammals, including most species of seal and sea lion, are taken by mammal-eating populations. Walrus and sea otters are taken less frequently. Several species of bird are also taken, including penguins, cormorants and sea gulls. Cephalopods, such as octopuses and a wide range of squids, are also targets.

Possessing great physical prowess, orcas use complex hunting strategies to find and subdue their prey. They will occasionally throw seals through the air in order to stun and kill them. While salmon are usually hunted by a single orca or a small group of individuals, herring are often caught using carousel feeding: the orcas force the herring into a tight ball by releasing bursts of bubbles or flashing their white undersides. The orcas then slap the ball with their tail flukes, either stunning or killing up to 10-15 herring with a successful slap. The herring are then eaten one at a time. Carousel feeding has only been documented in the Norwegian orca population and with some oceanic dolphin species. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke.

A captive orca in Friendship Cove discovered that it could regurgitate fish onto the surface, attract sea gulls, and eat them. Other orcas then learned the behavior by example.• Orcas at Sea World California have also been observed hunting birds.•

More specialized feeding techniques are used by various populations around the world. In Patagonia, orcas feed on South American sea lion and elephant seal pups in shallow water, even to the extent of temporarily stranding themselves. Orcas will spy-hop to locate seals resting on ice floes, and then create a wave to wash over the floe, causing the seal to be thrown into the water where a second orca waits to kill it. This behavior has only been recorded a few times and it is not known how often it occurs. The most recent recorded instance in April 2006 ended with the group of orcas returning the seal to the ice floe once they had shown the younger animals how to properly perform the technique.

On average, an orca eats 500 lbs. (227 kg) of food each day.• With this huge variety of prey, and no predators other than man, the orca is very much at the top of the food chain.

As with other dolphins, orcas are very vocal animals. They produce a variety of clicks and whistles that are used for communication and echolocation. The vocalization types vary with activity. While resting they are much quieter, merely emitting an occasional call that is distinct from those heard when engaging in more active behaviour.

Fish-eating resident groups of orcas in the Northeast Pacific tend to be much more vocal than transient groups living in the same waters. Scientists surmise that the main reason for this lies in the different hearing abilities of their prey. Resident orcas feed on fish, particularly Pacific salmon, a prey with poor underwater hearing that cannot detect orca calls at any significant distance. Transient orcas on the other hand feed mainly on marine mammals (primarily seals, sea lions, porpoises and dolphins) and occasionally on seabirds. Because all marine mammals have excellent underwater hearing, transients probably remain silent for much of the time to avoid detection by their acoustically-sensitive prey. For the same reason, mammal-hunting orcas tend to restrict their echolocation, occasionally using just a single click (called a cryptic click) rather than the long train of clicks observed in other populations.

Resident pods have group-specific dialects. Each pod has its own vocal repertoire or set of particular stereotyped underwater calls (call types). Every member of the pod seems to know all the call types of the pod, so it is not possible to identify a single animal using voice alone; only identification of a dialectal group is possible. A particular call type might be used by only one group or shared among several. The number of call types shared by two groups appears to be a function of their genealogical relatedness rather than their geographical distance. Two groups that share a common set of ancestors but have grown apart in distance are likely to have a similar set of call types. Calls are learned behaviour traits that are copied between related individals through vocal mimicry.

See also: Whale song

Although only scientifically identified as a species in 1758, the orca has been known to humans since prehistoric times. The desert culture of the Nazca created a Nazca line presumably representing an orca * (although it could be any whale) sometime between 200 BC and AD 600.

Indigenous tribes in the Pacific Northwest of North America such as the Tlingit, Haida, and Tsimshian featured the orca prominently in their religion and artwork.

The first description of an orca is given in Pliny the Elder's Natural History (written circa 70 AD). The aura of invincibility around the all-consuming orca was well-established by this time. Having observed the public slaughter of a whale stranded at a harbor near Rome, Pliny writes, "Orcas, (the appearance of which no image can express, other than an enormous mass of savage flesh with teeth), are the enemy of other whales... they charge and pierce them like warships ramming." (''Historia Naturalis'' 9.5.12)

Probably inspired by Pliny's description, creatures by the name of orca or "orc" have appeared throughout the history of Western literature. In Ludovico Ariosto's epic poem Orlando Furioso, the orca (sometimes translated "orc") was a sea-monster from whom the damsel Angelica was rescued by Orlando (Cantos 8 and 11), in an episode modelled on the story of Perseus and Andromeda. This Orca-like sea monster first appears in English in Michael Drayton's Polyolbion, an epic poem about Brutus the Trojan, the mythical founder of Great Britain. It later appears in John Milton's epic poem Paradise Lost; book 10 speaks of "The haunt of Seales and Orcs, and Sea-mews clang."

The orca's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquariums and various aquatic theme parks. The first orca capture and display occurred in Vancouver in 1964. Over the next 15 years around 60 or 70 orcas were taken from Pacific waters for this purpose. In the late 1970s and the first half of the 1980s, orcas were generally taken from Icelandic waters (50 in the five years to 1985). Since that time, orcas have been successfully bred in captivity and wild specimens are considerably rarer. Orcas in captivity may develop pathologies such as dorsal fin collapse, seen in 60-90% of captive males.

Several theories exists as to why the dorsal fin collapse occurs, namely that the cartilage that holds the fin erect is not yet strong enough to support the fin when the orca is placed in captivity. The hardening of the cartilage occurs in late adolescence, in which the orca spends much time in deep ocean waters, and it is theorized that the pressure the water exerts on the fin allows it to remain supported while the cartilage hardens. In captivity, however, the tank the whales reside in lack sufficient water pressure to produce this effect, and the fin collapses before the cartilage that would support it in nature solidifies. Another theory exists that states that the whale is almost always in a state of turning in a tank, since it is not large enough to allow swimming in one direction for any normal duration. The constant turning exerts pressure on the dorsal fin, which in turn causes it to collapse.

There have been incidents with orcas in captivity attacking humans. In 1991, a group of 3 orcas (Haida, Nootka, and Tillikum) killed a trainer named Keltie Byrne at Sealand in Victoria, British Columbia (where employees were not allowed in the water with orcas), the orcas apparently not knowing Byrne could not survive underwater. In 1999, at the SeaWorld park in Orlando, Florida, one of the same orcas allegedly killed a tourist who had sneaked into the orca's pool at night*. (The dead tourist, who was otherwise physically unharmed, was also thought to be a victim of hypothermia.) In late July 2004, during a show at the SeaWorld park in San Antonio, Texas, an orca pushed its trainer of ten years underwater and barred the way to the rim of the pool; the trainer could only be rescued from the animal after several minutes.

One of the more infamous incidents involving orca aggression took place in August 1989, when a dominant female orca, Kandu V, struck a newcomer orca, Corky II, with her mouth during a live show. Corky II had been imported from Marineland California just months prior to the incident. According to reports, a loud smack was heard across the stadium. Although trainers tried to keep the show rolling, the blow severed an artery near Kandu V's jaw, and she began spouting blood. The crowd was quickly ushered out, and after a 45-minute hemorrhage, Kandu V died. Opponents of these shows see these incidents as supporting their criticism.

SeaWorld continued to be under criticism from the Born Free Foundation over its continued captivity of the orca Corky II, who they want returned to her family, the A5 Pod, a large pod of orcas in British Columbia, Canada *.

Orcas in captivity have vastly reduced life expectancies, on average only living into their 20s. In the wild, females may live into their 80s. The captive environment also bears no resemblance to their wild habitat, and the social groups that the orcas are put into are completely foreign to those found in the wild *. Critics claim that captive life is stressful due to small tanks, false social groupings and chemically-altered water. Organisations such as the WSPA and the Whale and Dolphin Conservation Society campaign against the captivity of orcas. It should be noted that the technology to track orcas in the wild has only recently been developed. In the past, scientists have used visual identification of the whales and estimated their ages. While this does provide ideas of ages, it is not 100% accurate, which means the ages of most whales are merely estimated. The only whales whose ages are known for certain are those whose births have been recorded and those born in captivity.