s (1,800 lb). It is approximately 4.3 metres (14 ft) to 5.2 metres (017 ft) tall, although the tallest male recorded stood almost 6 metres (20 ft).The giraffe is related to other even-toed ungulates, such as deer and cattle, but is placed in a separate family, the Giraffidae, consisting of only the giraffe and its closest relative, the okapi. Its range extends from Chad in Central Africa to South Africa. Giraffes usually inhabit savannas, grasslands, or open woodlands. However, when food is scarce they will venture into areas with denser vegetation. They prefer areas with plenty of acacia growth. They will drink large quantities of water when available, which enables them to live for extended periods in dry, arid
Etymology
The species name camelopardalis (camelopard) is derived from its early Roman name, where it was described as having characteristics of both a camel and a leopard. The English word camelopard first appeared in the 14th century and survived in common usage well into the 19th century. The Afrikaans language retained it. The Arabic word ziraafa or zurapha, meaning "assemblage" (of animals), or just "tall", was used in English from the sixteenth century on, often in the Italianate form giraffa.
Taxonomy and evolution
The giraffe is one of only two living species of the family Giraffidae, along with the okapi. The family was once much more extensive, with numerous other species. The giraffids evolved from a 3 metres (9.8 ft) tall antelope-like mammal that roamed Europe and Asia some 30–50 million years ago.
The earliest known giraffid was Climacoceras, which still resembled deer, having large antler-like ossicones. It first appeared in the early Miocene epoch. Later examples include the genera Palaeotragus and Samotherium, which appeared in the early to mid-Miocene. They were both tall at the shoulder, and had developed the simple, unbranched ossicones of modern giraffids, but still had relatively short necks.
From the late Pliocene onwards, the variety of giraffids drastically declined, until only the two surviving species remained. The modern genus Giraffa evolved during the Pliocene epoch, and included a number of other long-necked species, such as Giraffa jumae, that do not survive today. Alan Turner proposes, in the 2004 book Evolving Eden, that giraffe ancestors initially had a dark coat with pale spots, and that the spots gradually became star-shaped, before eventually forming the reticulated pattern found today. The modern species, Giraffa camelopardalis, appeared during the Pleistocene 1 million years ago.[citation needed]
The evolution of the long necks of giraffes has been the subject of much debate. The standard story is that they were evolved to allow the giraffes to browse vegetation that was out of the reach of other herbivores in the vicinity, giving them a competitive advantage. However, an alternative theory proposes that the long necks evolved as a secondary sexual characteristic, giving males an advantage in "necking" contests (see below) to establish dominance and obtain access to sexually receptive females. This theory notes that giraffes frequently feed from relatively low-lying shrubs, and that the necks of males are significantly longer than those of females. However, this theory is not universally accepted, and some of the data supporting it has recently been challenged, lending support to the original proposal that neck length is related to browsing habits.
Subspecies
Different authorities recognize different numbers of subspecies, differentiated by colour and pattern variations and range. Some of these subspecies may prove to in fact be separate species. The subspecies recognized by various authorities include:
Reticulated Giraffe or Somali Giraffe (G. c. reticulata) – large, polygonal liver-coloured spots outlined by a network of bright white lines. The blocks may sometimes appear deep red and may also cover the legs. Range: northeastern Kenya, Ethiopia, Somalia.
Angolan Giraffe or Smoky Giraffe (G. c. angolensis) – large spots and some notches around the edges, extending down the entire lower leg. Range: Angola, Zambia.
Kordofan Giraffe (G. c. antiquorum) – smaller, more irregular spots that cover the inner legs. Range: western and southwestern Sudan, Cameroon.
Maasai Giraffe or Kilimanjaro Giraffe (G. c. tippelskirchi) – jagged-edged, vine-leaf shaped spots of dark chocolate on a yellowish background. Range: central and southern Kenya, Tanzania.
Nubian Giraffe (G. c. camelopardalis) – large, four-sided spots of chestnut brown on an off-white background and no spots on inner sides of the legs or below the hocks. Range: eastern Sudan, northeast Congo.
Rothschild Giraffe or Baringo Giraffe or Ugandan Giraffe (G. c. rothschildi) – deep brown, blotched or rectangular spots with poorly defined cream lines. Hocks may be spotted. Range: Uganda, north-central Kenya.
South African Giraffe (G. c. giraffa) – rounded or blotched spots, some with star-like extensions on a light tan background, running down to the hooves. Range: South Africa, Namibia, Botswana, Zimbabwe, Mozambique.
Thornicroft Giraffe or Rhodesian Giraffe (G. c. thornicrofti) – star-shaped or leafy spots extend to the lower leg. Range: eastern Zambia.
West African Giraffe or Nigerian Giraffe (G. c. peralta) – numerous pale, yellowish red spots. Range: Niger.
Some scientists regard Kordofan and West African Giraffes as a single subspecies; similarly with Nubian and Rothschild's Giraffes, and with Angolan and South African Giraffes. Further, some scientists regard all populations except the Masai Giraffes as a single subspecies. By contrast, scientists have proposed four other subspecies — Cape Giraffe (G. c. capensis), Lado Giraffe (G. c. cottoni), Congo Giraffe (G. c. congoensis), and Transvaal Giraffe (G. c. wardi) — but none of these is widely accepted.
Though giraffes of these populations interbreed freely under conditions of captivity, suggesting that they are subspecific populations, genetic testing published in 2007 has been interpreted to show that there may be at least six species of giraffe that are reproductively isolated and not interbreeding, even though no natural obstacles, like mountain ranges or impassable rivers block their mutual access. In fact, the study found that the two giraffe populations that live closest to each other— the reticulated giraffe (G. camelopardalis reticulata) of north Kenya, and the Masai giraffe (G. c. tippelskirchi) in south Kenya— separated genetically between 0.13 and 1.62 million years BP, judging from genetic drift in nuclear and mitochondrial DNA.
The implications for conservation of as many as eleven such cryptic species and sub-species were summarised by David Brown for BBC News: "Lumping all giraffes into one species obscures the reality that some kinds of giraffe are on the brink. Some of these populations number only a few hundred individuals and need immediate protection."
Anatomy and morphology
Male giraffes are up to 5.5 metres (18 ft) tall at the horn tips, and weigh between 800 and 1,930 kilograms (1,800 and 4,300 lb). Females are between 4 and 4.5 metres (13 and 14.8 ft) tall and weigh between 550 and 1,180 kilograms (1,200 and 2,600 lb). The coat is made up of brown blotches or patches separated by lighter hair. Each giraffe has a unique coat pattern. Wild giraffes have a lifespan close to 13 years while those in captivity live up to 25 years.
Horns
Both sexes have horns, although the horns of a female are smaller. The prominent horns are formed from ossified cartilage, and are called ossicones. The appearance of horns is a reliable method of identifying the sex of giraffes, with the females displaying tufts of hair on the top of the horns, whereas males' horns tend to be bald on top — an effect of necking in combat. Males sometimes develop calcium deposits which form bumps on their skull as they age, which can give the appearance of up to three additional horns.
Legs and pacing
Giraffes also have slightly elongated forelegs, about 10% longer than their hind legs, and can reach a sprint speed of up to 60 km/h (37nbspm/h). It cannot sustain a lengthy chase. Its leg length compels an unusual gait with the left legs moving together followed by right (similar to pacing) at low speed, and the back legs crossing outside the front at high speed. When hunting adult giraffes, lions try to knock the lanky animal off its feet and pull it down. Giraffes are difficult and dangerous prey. The giraffe defends itself with a powerful kick. A single well-placed kick from an adult giraffe can shatter a lion's skull or break its spine. Lions are the only predators which pose a serious threat to an adult giraffe.
Neck
Giraffes have long necks which they use to browse tree leaves. The neck has seven highly lengthened vertebrae, otherwise the usual number of vertebrae for a mammal. However, some zoologists claim there are eight. Moreover, the vertebrae are separated by very flexible joints, the base of the neck has spines which project upward to form a hump over the shoulders and anchor muscles hold the neck upright.
Circulatory system
Modifications to the giraffe's structure have evolved, particularly to the circulatory system. A giraffe's heart, which can weigh up to 10 kg (22 lb) and measure about 60 cm (2 ft) long, must generate approximately double the normal blood pressure for an average large mammal to maintain blood flow to the brain. In the upper neck, a complex pressure-regulation system called the rete mirabile prevents excess blood flow to the brain when the giraffe lowers its head to drink. Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). In other animals such pressure would force the blood out through the capillary walls; giraffes, however, have a very tight sheath of thick skin over their lower limbs which maintains high extravascular pressure in the same way as a pilot's g-suit.
Behaviour
Social structure and breeding habits
Female giraffes associate in groups of a dozen or so members, occasionally including a few younger males. Younger males tend to live in "bachelor" herds, with older males often leading solitary lives. While research from the 1970s concluded that giraffes did not socialize, later research found that giraffes did form attachments to other giraffes, with giraffes spending 15% of their time grazing with the giraffes they are close to and only 5% of their time grazing with giraffes who are strangers.
Reproduction is polygamous, with a few older males impregnating all the fertile females in a herd. Male giraffes determine female fertility by tasting the female's urine in order to detect estrus, in a multi-step process known as the Flehmen response.
Giraffes will mingle with the other herbivores in the African bush. Their company is beneficial, since they are tall enough to have a much wider scope of an area and will watch for predators.Female giraffes associate in groups of a dozen or so members, occasionally including a few younger males. Younger males tend to live in "bachelor" herds, with older males often leading solitary lives. While research from the 1970s concluded that giraffes did not socialize, later research found that giraffes did form attachments to other giraffes, with giraffes spending 15% of their time grazing with the giraffes they are close to and only 5% of their time grazing with giraffes who are strangers.
Reproduction is polygamous, with a few older males impregnating all the fertile females in a herd. Male giraffes determine female fertility by tasting the female's urine in order to detect estrus, in a multi-step process known as the Flehmen response.
Giraffes will mingle with the other herbivores in the African bush. Their company is beneficial, since they are tall enough to have a much wider scope of an area and will watch for predators.
Reproduction
Giraffe gestation lasts between 400 and 460 days, after which a single calf is normally born, although twins occasionally occur. The mother gives birth standing up and the embryonic sack usually bursts when the baby falls to the ground. Newborn giraffes are about 1.8 m (6 ft) tall.
Within a few hours of being born, calves can run around and are indistinguishable from a week-old calf; however, for the first two weeks, they spend most of their time lying down, guarded by the mother. The young can fall prey to lions, leopards, spotted hyenas, and wild dogs. It has been speculated that their characteristic spotted pattern provides a certain degree of camouflage. Only 25 to 50% of giraffe calves reach adulthood; the life expectancy is between 20 and 25 years in the wild and 28 years in captivity.
Necking
Male giraffes often engage in necking, which has been described as having various functions. One of these is combat. Battles can be fatal, but are more often less severe, generally ending when one giraffe surrenders to the other. The longer the neck, and the heavier the head at the end of the neck, the greater the force a giraffe is able to deliver in a blow. It has also been observed that males that are successful in necking have greater access to estrous females, so the length of the neck may be a product of sexual selection.
After a necking duel, a giraffe can land a powerful blow with his head — occasionally knocking a male opponent to the ground. These fights rarely last more than a few minutes or end in physical harm.
Another function of necking is sexual, in which two males caress and court each other, leading up to mounting and climax. Such interactions between males are more frequent than heterosexual coupling. In one study, up to 94% of observed mounting incidents took place between two males. The proportion of same sex activities varied between 30 and 75%, and at any given time one in twenty males were engaged in non-combative necking behaviour with another male. Only 1% of same-sex mounting incidents occurred between females.
Diet
The giraffe browses on the twigs of trees, preferring trees of the genera Acacia, Commiphora and Terminalia, and also eats grass and fruit. The tongue is tough due to the giraffe's diet, which can include tree thorns. In Southern Africa, giraffes feed on all acacias, especially Acacia erioloba, and possess a specially adapted tongue and lips that are tough enough to withstand the vicious thorns of this plant. A giraffe can eat 65 pounds (29 kg) of leaves and twigs daily, but can survive on just 15 pounds (6.8 kg). The giraffe requires less food than typical grazing animals because the foliage it eats has more concentrated nutrition and it has a more efficient digestive system. During the wet season, food is abundant and giraffes disperse widely, but during the dry season they need to congragate around evergreen trees and bushes.[ As a ruminant, it first chews its food, then swallows for processing and then visibly regurgitates the semi-digested cud up their necks and back into the mouth, in order to chew again. This process is usually repeated several times for each mouthful. The giraffe can surivive without water for extended periods. A giraffe will clean off any bugs that appear on its face with its extremely long tongue (about 45 centimetres (18 in)).
Sleeping
The giraffe has one of the shortest sleep requirements of any mammal, which is between ten minutes and two hours in a 24-hour period, averaging 1.9 hours per day.
Communication
Although generally quiet and non-vocal, giraffes have been heard to make various sounds. Courting males will emit loud coughs. Females will call their young by whistling or bellowing. Calves will bleat, moo, or make mewing sounds. In addition, giraffes will grunt, snort, hiss, or make strange flute-like sounds. Recent research has shown evidence that the animal communicates at an infrasound level.
Stereotypic behavior
Many animals when kept in captivity, such as in zoos, display abnormal behaviours. Such unnatural behaviours are known as stereotypic behaviours. In particular, giraffes show distinct patterns of stereotypic behaviours when removed from their natural environment. Due to a subconscious response to suckle milk from their mother, something which many human-reared giraffes and other captive animals do not experience, giraffes resort instead to excessive tongue use on inanimate objects.
Human interactions
ConservationOverall, the giraffe is regarded as "Least Concern" from a conservation perspective by the International Union for Conservation of Nature (IUCN). However, at least one subspecies, the West African or Nigerian Giraffe (G. c. peralta), has been classified as endangered.
Giraffes are hunted for their tails, hides and meat. The tails are used as good luck charms, thread and flyswatters. In addition, habitat destruction also hurts the giraffe. In the Sahel trees are cut down for firewood and to make way for livestock. Normally, giraffes are able to cope with livestock since they feed in the trees above their heads. The giraffe population is shrinking in West Africa. However, the populations in eastern and southern Africa are stable and, due to the popularity of privately owned game ranches and sanctuaries (i.e. Bour-Algi Giraffe Sanctuary), are expanding. The giraffe is a protected species in most of its range. The total African giraffe population has been estimated to range from 110,000 to 150,000. Kenya (45,000), Tanzania (30,000), and Botswana (12,000), have the largest national populations.
Scientific inspiration
Giraffes have been used as examples for introducing ideas in evolution, especially to illustrate the ideas of Lamarck. Lamarck believed that the giraffe's long neck developed as a result of ancestral giraffe's reaching to browse on the leaves of tall trees.
The coat patterns of several species of giraffe have been modelled using reaction-diffusion mechanisms.
Source:http://en.wikipedia.org/wiki/Giraffe
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