Saturday, September 10, 2011

Bottle Nose Dolphin

Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins.Recent molecular studies show the genus contains two species, the common bottlenose dolphin (Tursiops truncatus) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus), instead of one. They inhabit warm and temperate seas worldwide.
Bottlenose dolphins live in groups typically of 10–30 members, called pods, but group size varies from single individuals up to more than 1,000. Their diet consists mainly of forage fish. Dolphins often work as a team to harvest fish schools, but they also hunt individually. Dolphins search for prey primarily using echolocation, which is similar to sonar. They emit clicking sounds and listen for the return echo to determine the location and shape of nearby items, including potential prey. Bottlenose dolphins also use sound for communication, including squeaks and whistles emitted from the blowhole and sounds emitted through body language, such as leaping from the water and slapping their tails on the water surface.
They are grey, varying from dark grey at the top near the dorsal fin to very light grey and almost white at the underside. This counter shading makes it hard to see, both from above and below, when swimming. Adults range in length between 2 and 4 meters (6.6 and 13 ft), and in weight between 150 and 650 kilograms (330 and 1,400 lb).Males are on average slightly longer and considerably heavier than females. In most parts of the world, the adult's length is about 2.5 m (8.2 ft), with weight ranges between 200 and 300 kilograms (440 and 660 lb). Their size varies considerably with habitat. Except in the eastern Pacific, dolphins in warmer, shallower waters tend to be smaller than those in cooler pelagic waters. A survey in the Moray Firth in Scotland, the world's second northernmost dolphin population, recorded an average adult length of just under 4 m (13 ft) compared with a 2.5 m (8.2 ft) average in a population off the coast of Florida.
There have been numerous investigations of bottlenose dolphin intelligence. Research on bottlenose dolphins has examined mimicry, use ofartificial language, object categorization and self-recognition. Their considerable intelligence has driven interaction with humans. Bottlenose dolphins are popular from aquarium shows and television programs such as Flipper. They have also been trained by militaries to locate sea mines or detect and mark enemy divers. In some areas, they cooperate with local fishermen by driving fish into their nets and eating the fish that escape. Some encounters with humans are harmful to the dolphins: people hunt them for food, and dolphins are killed inadvertently as abycatch of tuna fishing.
Their elongated upper and lower jaws form what is called a rostrum, or snout, which gives the animal its common name. The real, functional nose is the blowhole on top of its head; the nasal septum is visible when the blowhole is open.
Bottlenose dolphins can live for more than 40 years. However, one study of a population off Sarasota, Florida indicated an average lifespan of 20 years or less.

The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and do not contain bone or muscle. The animal propels itself by moving the flukes up and down. The pectoral flippers (at the sides of the body) are for steering; they contain bones homologous to the forelimbs of land mammals. A bottle nose dolphin was discovered in Japan that has two additional pectoral fins, or "hind legs", at the tail, about the size of a human's pair of hands. Scientists believe a mutation caused the ancient trait to reassert itself as a form of atavism
Both genders have genital slits on the underside of their bodies. The male can retract and conceal its penis through its slit. The female's slit houses its vagina and anus. Females have two mammary slits, each housing one nipple, one on each side of the genital slit. Stewart, R. (2002). "Female Reproductive Systems". In Perrin, W.; Wursig, B. and Thewissen, J.. Encyclopedia of Marine Mammals. Academic Press. pp. 422–428. ISBN 0-12-551340-2.</ref> The ability to stow their reproductive organs (especially in males) allows for maximum hydrodynamics. The breeding season produces significant physiological changes in males. At that time, testes enlarge, enabling it to hold more sperm. Large amounts of sperm allow a male to wash away the previous suitor's sperm, while leaving some of his own for fertilization. Also, sperm concentration markedly increases. Having less sperm for out-of-season social mating means it wastes less. This suggests sperm production is energetically expensive. Males have large testes in relation to their body size.
Bottlenose dolphins have 18 to 28 conical teeth on each side of each jaw.
During the breeding season, males compete for access to females. Such competition can take the form of fighting other males or of herding females to prevent access by other males. In Shark Bay, male bottlenose dolphins have been observed working in pairs or larger groups to follow and/or restrict the movement of a female for weeks at a time, waiting for her to become sexually receptive. These coalitions will fight with other coalitions for control of females.
Mating occurs belly to belly.Dolphins have been observed engaging in intercourse when the females are not in their estrus cycles and cannot produce young, as well as when they can. The gestation period averages 12 months Births can occur at any time of year, although peaks occur in warmer months.The young are born in shallow water, sometimes assisted by a (possibly male) "midwife", and usually only a single calf is born.Twins are possible but rare. Newborn bottlenose dolphins are between 0.8–1.4 m (2.6–4.6 ft) 9–30 kg (20–66 lb) kilograms, with Indo-Pacific bottlenose dolphin infants generally smaller than common bottlenose dolphin infants. To accelerate nursing, the mother can eject milk from her mammary glands. The calf suckles for 18 to 20 months, and continues to closely associate with its mother for several years after weaning. Females sexually mature at ages 5–13, males at ages 9–14. Females reproduce every two to six years. Georgetown University professor Janet Mann argues the strong personal behavior among male calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing these dolphins as adults are inseparable, and that early bonds aid protection as well as in locating .

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