The orca (Orcinus orca) is the largest member of the oceanic dolphin family. It is the second-most widely distributed mammal on Earth (after humans) and is found in all the world's oceans. It is a versatile predator, eating fish, turtles, birds, seals, sharks and even other juvenile and small cetaceans. This puts the orca at the pinnacle of the marine food chain. The orca also attacks whales, in particular gray whales.

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The name "killer whale" is widely used in common English. However, since the 1960s, "orca" has steadily grown in popularity as the common name to identify the species, and both names are now used - leading to confusion. Furthermore, the 'killer' in "killer whale" is often wrongly assumed to imply that the creature is a killer of humans. It is this group’s ruthless hunting and eating habit that gained orca the nick name "killer whales." Today it is recognized that the orca is a dolphin rather than a whale and that it is not a danger to humans. Aside from a boy who was charged (but not grabbed) while swimming in a bay in Alaska, there have been no confirmed attacks on humans. Killer whales

The name "orca" was originally given to these animals by the ancient Romans, possibly referring to a species of whale. A pod of orcas is capable of taking down a large whale.

There are three distinct groups of orcas.
Transient orcas generally travel in small groups, usually up to 7 or 8 animals. These are referred to as groups rather than pods because they do not have as strong a social bond, and do not necessarily remain as a family unit, probably due to their diet. They are generally seen cruising along the shorelines hunting for prey. Often, to avoid injury, they will disable their prey before killing and eating it. This may involve throwing it in the air, slapping it with their tails, ramming it, or breaching and landing on it. The whole process can be quite lengthy at times, seeming to be like torture for the prey, but is primarily for safety and training for the young killer whales. orca whaleFemale transients are characterized by pointed dorsal fin tips. The range for transient killer whales is unknown, but may be as much as 1500 miles or more.

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 orca’s diet consists primarily of fish, including salmon and herring and they frequent areas where their preferred fish are abundant. They are continually on the move, sometimes traveling as much as 100 miles in a day.

Offshore orca were given this name for what the name implies. They remain offshore cruising the open oceans feeding primarily on fish. They have been seen traveling in groups of up to 60 animals. Currently there is little known about the habits of this population, but they can be distinguished genetically from the residents and transients. Female offshores are characterized by dorsal fin tips that are continuously rounded.

Physical characteristics
The animals are distinctively marked, with a black back, white chest and sides and a white patch above and behind the eye. They have a heavy and stocky body and a large dorsal fin with a dark gray "saddle patch" behind it. Males can be up to 9.5 m long (31 ft) and weigh in excess of 6 tons; females are smaller, reaching up to 8.5 m (28 ft) and a weight of about 5 tons. Calves at birth weigh about 180 kg and are about 2.4 m long (8 ft). Unlike most dolphins, the pectoral fin of an orca is large and rounded — more of a paddle than other dolphin species. Pectoral fins of males are significantly larger than those of females. At about 1.8 m (6 ft), the dorsal fin of the male is more than twice the size of the female's, and is more of a triangle shape — a tall, elongated isosceles triangle, whereas the dorsal fin of the female is shorter and generally more curved. Nicks, cuts and scrapes on these fins, as well as distinctive features of each fin, help scientists identify individuals. There are also minor variations in physical characteristics between resident and transient Killer Whales.killer whales

Large male orcas are very distinctive and are unlikely to be confused with any other sea creature. When seen from a distance in temperate waters, females and juveniles can be confused with various other species, such as the false killer whale or Risso's dolphin.
orca whale

Females become mature at around 15 years of age. From then they have periods of polyestrous cycling with non-cycling periods of between three and sixteen months. The gestation period varies from fifteen to eighteen months. Mothers calve, with a single offspring, about once every five years. In analysed resident pods, birth occurs at any time of year, with the most popular months being those in winter. New-born mortality is very high — one survey suggested that nearly half of all calves fail to reach the age of six months. Calves nurse for up to two years, but will start to take solid food at about twelve months. Cows breed until the age of 40, meaning that on average they raise five offspring. Typically females live to the age of fifty, but may survive well into their eighties or nineties in exceptional cases. Males become sexually mature at the age of 15, but do not typically reproduce until age 21. Males live to about 30 on average, and to 50 in exceptional cases.

Social interaction
Orcas often raise their body out of the water in a behaviour called spyhopping. Scientists debate its purpose.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 traveling 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.

Killer whale Matrilines form loose aggregations called pods, consisting on average of about 18 animals. Members of a pod all have the same dialect 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 orca is an apex predator and the array of species on which orcas prey is extremely diverse. 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 other cetacean's body, or by simply observing the 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 killer whales 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 killed by drowning.
killer whale

Possessing great physical prowess as well as intelligence, Orcas use complex hunting strategies to find and subdue their prey. They sometimes will throw seals to one another through the air in order to stun and kill the animal. 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 underside. 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. 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.

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.

Vocal Behaviour

Orcas, commonly breach, often lifting their entire body out of the water.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, perhaps unsurprisingly, they are much quieter, merely emitting an occasional call that is distinct from those heard when engaging in more active behaviour.Orca whale tail

Fish-eating resident groups of killer whales 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 killer whales feed on fish, particularly Pacific salmon, a prey with poor underwater hearing that cannot detect killer whale calls at any significant distance. Transient killer whales 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 killer whales 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.

Pod of orca whales

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 a dialectal group. A particular call type might be used by only one group or shared among several.

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