Killer Whale - biology.

Killer Whale - biology. I INTRODUCTION Killer Whale or Orca, aquatic mammal that is the largest member of the dolphin family. The killer whale is so named because of its voracious appetite for fish, seabirds, sea turtles, and aquatic mammals. But this name can cause confusion. The killer whale is a member of the dolphin family Delphinidae. This family belongs to the mammalian order Cetacea, which also includes a number of whale families, as well as the porpoise family Phocoenidae. Killer whales occur in more parts of the world than any other aquatic mammal. They inhabit all the oceans, both in the open ocean and close to shore. They are more commonly found in colder waters, but they also occur in the warmer waters of the Bahamas, the Caribbean, and Hawaii. Killer whales have even been seen in some rivers, including the Loire and Seine rivers in France, the Elbe River in the Czech Republic, and the Columbia River in the western part of the United States. The killer whale's ferocious eating habits have long aroused both fear and respect for the animal in many indigenous peoples, especially the Native Americans of the Pacific Northwest. The Tlingit, Kwakiutl, and Haida tribes incorporate images of the animal into their totem art, and illustrations of the animal appear on masks, dishes, helmets, and blankets. Despite its fierce reputation, some cultures, such as the Tlingit, believe that the killer whale is a kindly guardian of ocean food. They believe the presence of killer whales helps humans harvest large amounts of fish. II PHYSICAL CHARACTERISTICS The killer whale's scientific name Orcinus orca is derived from the Latin word orcas, meaning "cask" or "barrel," referring to the animal's broad, rounded shape. Unlike most dolphins, male and female killer whales exhibit considerable differences in size and appearance. Adult males, known as bulls, can reach up to 9.8 m (32 ft) in length and weigh over 5,500 kg (12,100 lb). Adult females, known as cows, are smaller, growing to 8.5 m (28 ft) in length and weighing as much as 3,800 kg (8,400 lb). Both male and female killer whales have bold black-and-white coloring. The animals are glossy black over most of the body, with a white belly and striking white patches above the eye. The shape of a fainter grayish-white patch just behind the dorsal fin is unique to each killer whale and scientists use this marking as one way to identify individual animals. The killer whale has a round, blunt head. Large powerful jaws are lined with 46 to 50 spikelike teeth adapted for ripping and tearing prey but not for chewing. A prominent triangular dorsal fin extends from the middle of the back. This fin is particularly large in adult males, growing to 1.8 m (5.9 ft) tall. The dorsal fins vary in appearance among individual killer whales--they may be curvy, twisted, flopped over, or even scarred from run-ins with boat propellers. Scientists use dorsal fins to help identify individual animals. The flippers of killer whales are broad and paddle-shaped, and the flukes (horizontal lobes on the tail) sometimes curl downward, especially in adults. Both the flippers and tail flukes of adult males are considerably larger than those of adult females. Killer whales have a thick layer of blubber (body fat) that lies just beneath the skin. This layer of fat insulates the animal, enabling it to maintain a body temperature that ranges from 36.4° to 38°C (97.5° to 100.4°F), even in the most frigid waters. Like all mammals, killer whales breathe with lungs. Air enters the lungs through a single blowhole located on the top of the head. At the water's surface, the killer whale inhales and closes a muscular flap covering the blowhole before diving underwater. The animal opens its blowhole and exhales just before reaching the surface of the water. Killer whales are among the fastest animals in the sea, reaching swimming speeds of up to 50 km/h (30 mph) for short periods of time. While underwater, killer whales can dive to depths of around 61 m (200 ft). During a dive, the animal's heart rate slows from 60 beats per minute to 30 beats per minute. Oxygen-carrying blood is shunted away from the extremities and channeled toward the heart, lungs, and brain, where more oxygen is needed. These adaptations enable the animal to conserve oxygen while underwater. III SOCIAL BEHAVIOR Killer whales live in family groups called matrilines. Each matriline is composed of an adult female and her offspring. Male parents of the offspring do not live with the matrilineal group. Some male and female offspring stay with their matrilineal group for life. Other matrilineal groups are less stable, with members that come and go. Two or more matrilines may form a larger social group called a pod, consisting of 40 or more members. In the Pacific Northwest, scientists have identified two types of killer whale pods. Resident pods permanently inhabit a particular area that may cover over 800 sq km (308 sq mi). Transient pods do not have a permanent territory and sometimes swim more than 1,000 km (600 mi) in two or three days. Killer whales communicate with each other primarily by sound, emitting clicks, squeaks, and whistles. Each pod uses a unique group of calls, called a dialect. The animals also communicate with each other by slapping their flippers and flukes on the water. They use touch to communicate as well. Sometimes after aggressive play or fighting among a group of killer whales, one killer whale will pat another killer whale with its fin. Scientists believe this action expresses reconciliation. Killer whales regularly exhibit such behaviors as spy-hopping (hanging vertically in the water with the head partially above water) and breaching (jumping clear of the water and landing on the back or side). Scientists theorize that these behaviors may be displays of dominance used in courtship or they may enable the killer whales to view their surrounding area. IV DIET Killer whales are ravenous feeders, eating up to 136 kg (300 lbs) of food a day. They feed on fish (including sharks and rays), squid, and marine birds, as well as more than 35 different species of marine mammals, including sea otters, seals, sperm whales, minke whales, humpback whales, gray whales, and blue whales. A killer whale's diet varies depending on its location. In the Antarctic, for instance, the animal's diet consists of about 67 percent fish, 27 percent marine mammals, and 6 percent squid. In the Bering Sea near Alaska, the diet is about 65 percent fish, 20 percent squid, and 15 percent marine mammals. Scientists have observed that resident and transient killer whales in the same area have a different diet. In the Pacific Northwest of the United States and the Pacific Provinces of Canada, for example, resident populations feed mainly on salmon and other near-shore fishes, while transient populations feed primarily on harbor seals and porpoises. Killer whales often hunt in packs, working together to encircle and herd prey into a small area before attacking. While hunting, killer whales rely on echolocation to gather information about their surroundings. A killer whale emits high-frequency clicks that bounce off objects. The animal analyzes the reflected sound waves to locate prey and avoid obstacles. V REPRODUCTION Mating occurs more often among killer whales of different pods to avoid inbreeding within pods. About 16 to 18 months after mating, females give birth to a single calf. Newborn calves weigh about 200 kg (440 lb) and are about 2.5 m (8 ft) long. Mothers nurse their calf for 14 to 18 months, although mothers continue to be protective of their young long after the offspring have been weaned. Scientists do not know how long killer whales live in the wild. Scientists estimate that male killer whales in the Pacific Northwest have an average life span of about 30 years, while females can live up to 60 years. VI KILLER WHALES AND HUMANS In captivity killer whales are very responsive to humans. They are easily trained to dive, leap, and fetch objects on cue, making them popular attractions at aquatic zoos. Scientists also use captive killer whales as research animals to study behaviors--such as echolocation, reproduction, growth, and development--that are difficult to study in the wild. In the wild, killer whales are protected by both U.S. and international law. The Marine Mammal Protection Act, passed by the United States Congress in 1972, makes it a federal offense to harm or harass any marine mammal. Since 1982 the International Whaling Commission has banned the commercial hunting of all whales, dolphins, and porpoises. The killer whale is considered at low risk for extinction by the World Conservation Union (IUCN), a nongovernmental organization that compiles global information on endangered species. Even with legal protection, however, scientists fear that a number of human-created problems threaten killer whales. Some killer whales have been captured from the waters around Japan and Russia for public display. Scientists suspect that widespread pollution, including chemicals in the oceans from agricultural runoff and oil spills, has damaged the ocean habitats in much of the killer whale's range. Fish and other prey absorb chemical contaminants into their bodies, and killer whales feed on these contaminated animals. As a result, the number of killer whales debilitated by disease has increased. In the Pacific Northwest, pollution and overfishing have reduced salmon populations, limiting the availability of a favorite killer whale prey. Direct interactions with humans have also affected killer whale populations. Whale-watching expeditions are a popular boating activity. Boaters have cruised too close to killer whale pods, preventing the animals from hunting for food or inadvertently separating mothers from their calves. Easily disturbed by boaters, killer whales may move quickly to evade a boat or they may exhibit aggressive defensive behaviors. These actions sometimes cause boats to accidentally collide with the animals and injure them. In addition, fishing crews occasionally entangle killer whales in their large nets by accident. Scientists fear that these human interactions may be the reason that the killer whale population in the Pacific Northwest has plummeted by 20 percent since 1996. Scientific classification: The killer whale belongs to the family Delphinidae of the suborder Odontoceti, order Cetacea. It is classified as Orcinus orca. Reviewed By: Daniel K. Odell Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.