Wednesday, August 31, 2011

killer whale

The killer whale is the largest member of the dolphin family.Wild killer whales are not considered a threat to humans, although there have been cases of captives killing or injuring their handlers at marine theme parks. Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers.

Killer whales distinctively bear a black back, white chest and sides, and a white patch above and behind the eye. Calves are born with a yellowish or orange tint, which fades to white. Killer whales have a heavy and robust body (more so than other dolphins) and a large dorsal fin up to 2 metres (6.6 ft) tall. Behind the fin, they have a dark grey "saddle patch" across the back. Antarctic killer whales may have pale grey to nearly white backs. Adult killer whales are very distinctive and are not usually confused with any other sea creature.Males typically range from 6 to 8 meters (20–26 ft) long and weigh in excess of 6 tonnes (5.9 long tons; 6.6 short tons).Females are smaller, generally ranging from 5 to 7 meters (16–23 ft) and weighing about 3 to 4 tonnes (3.0 to 3.9 long tons; 3.3 to 4.4 short tons). The largest male killer whale on record was 9.8 meters (32 ft), weighing over 10 tonnes (9.8 long tons; 11 short tons), while the largest female was 8.5 meters (28 ft), weighing 7.5 tonnes (7.4 long tons; 8.3 short tons). Calves at birth weigh about 180 kilograms (400 lb) and are about 2.4 meters (7.9 ft) long. The killer whale's large size and strength make it among the fastest marine mammals, able to reach speeds in excess of 30 knots (56 km/h).Killer whale pectoral fin are large and rounded, resembling paddles. Males have significantly larger pectoral fins than females. At about 1.8 meters (5.9 ft) the male's dorsal fin is more than twice the size of the female's and is more of a triangular shape—a tall, elongated isosceles triangle—whereas hers is shorter and more curved.Males and females also have different patterns of black and white skin in the genital area.
Individual killer whales can often be identified from the dorsal fin and saddle patch. Variations such as nicks, scratches, and tears on the dorsal fin and the pattern of white or grey in the saddle patch are unique. Published directories contain identifying photographs and names for hundreds of North Pacific animals. Photo identification has enabled the local population of killer whales to be counted each year rather than estimated and has enabled great insight into lifecycles and social structures.
Female killer whales mature at around age 15. They then have periods of poly estrus cycling with non-cycling periods of between 3 and 16 months. gestation varies from 15 to 18 months. Mothers calve, with usually a single offspring, about once every 5 years. In resident pods, birth occurs at any time of year, although winter is the most popular. Mortality is extremely high during the first six to seven months of life, when 37–50% of all calves die.weaning begins at about 12 months and completes by the age of two. According to observations in several regions, all male and female killer whale pod members participate in the care of the young. Killer Whales and Pilot whales are the only species in which the females go through menopause and live for decades after they have finished breeding.
Females breed until age 40, meaning that on average they raise five offspring. The lifespan of wild females averages 50 years, with a maximum of 80–90 years. Males sexually mature at the age of 15 but do not typically reproduce until age 21. Wild males live around 29 years on average, with a maximum of 50–60 years. One male, known as old Tom, was reportedly spotted every winter between the 1840s and 1930 off New South Wales Australia. This would have made him up to 90 years old. Examination of his teeth indicated he died around age 35, but this method of age determination is now believed to be inaccurate for older animals. One male well known to researchers in the Pacific Northwest called Ruffles (J1) is estimated to have been born in 1951, making him 58 years old in 2009.Captive killer whale lifespans are typically significantly shorter, usually less than 25 years; however, numerous individuals are alive in their thirties, and a few have reached their 40s. In many instances, the lifespans of killer whales depend on the will of the animal

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