Tuesday, July 7, 2009

Orca Whales (Killer Whales)

The killer whale or orca is the largest species of the Dolphin family. It is found in all the world's oceans, from the Arctic and Antarctic regions to warm, tropical seas. Killer whales are versatile and opportunistic marine apex predators. Some populations feed mostly on bony fish while others hunt sharks and marine mammals, including sea lions, seals, walruses and even large whales. There are up to five distinct killer whale types distinguished by geographical range, preferred prey items and physical appearance. Some of these may be separate races, subspecies or even species. Killer whales are social, some populations are composed of matrilineal family groups.

The diet of these killer whales consists almost exclusively of marine mammals; they do not eat fish. Transients in southern Alaska generally travel in small groups, usually of two to six animals. Unlike residents, transients may not always stay together as a family unit. Pods consist of smaller groups with less persistent family bonds and vocalizing in less variable and less complex dialects. Female transients are characterized by dorsal fins that are more triangular and pointed than those of residents. The gray or white area around the dorsal fin, known as the "saddle patch", often contains some black coloring in residents. However, the saddle patches of transients are solid and uniformly gray. Transients roam widely along the coast, some individuals have been sighted in Southern Alaska and later in California.

Some killer whales cruise the open oceans and are believed to feed primarily on schooling fish. However, because of the large presence of scarred and nicked dorsal fins resembling that of the mammal-hunting transients, the possibility that they eat mammals and sharks cannot be ruled out. They have mostly been encountered off the west coast of Vancouver Island and near the Queen Charlotte Islands. 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. Offshores appear to be shorter than the residents and the transients and females are characterized by dorsal fin tips that are continuously rounded.

Whales make a wide variety of communicative sounds, and each pod has distinctive noises that its members will recognize even at a distance. They use echolocation to communicate and hunt, making sounds that travel underwater until they encounter objects, then bounce back, revealing their location, size, and shape.

Killer whales are protective of their young, and other adolescent females often assist the mother in caring for them. Mothers give birth every three to ten years, after a 17-month pregnancy. Orcas are immediately recognizable by their distinctive black-and-white coloring and are very intelligent.