Giraffe

From Wikipedia, the free encyclopedia

The Giraffe (Giraffa camelopardalis) is an African even-toed ungulate mammal, the tallest of all land-living animal species. Males can be 4.8 to 5.5 metres (16 to 18 feet) tall and weigh up to 1,360 kilograms (3,000 pounds). The record-sized bull was 5.87 m (19.2 feet) tall and weighed approximately 2,000 kg (4,400 lbs.). ^[2] Females are generally slightly shorter and weigh less.

The giraffe is related to deer and cattle, but is placed in a separate family, the Giraffidae, consisting only of the giraffe and its closest relative, the okapi. Its range extends from Chad to South Africa.

Etymology and history

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 .^[3] The English word camelopard first appeared in the 14th century, and survived in common usage well into the 19th century. A number of European languages retain it. The Arabic word الزرافة 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.

Physical characteristics

Male giraffes are around 15–17 feet tall at the horn tips, and weigh 1700–4200 lb. Females are one to two feet shorter and weigh several hundred pounds less than males. Both sexes have horns, although the horns of a female are smaller. The prominent horns are formed from ossified cartilage and are called ossicones. Males sometimes develop calcium deposits which form bumps on their skull as they age, which can give the appearance of up to three further horns.^[4]

Giraffes have spots covering their entire bodies, except their underbellies, with each giraffe having a unique pattern of spots. They have long, prehensile tongues that are distinctly blue-black to protect from sunburn. Giraffes have long necks, which they use to browse the leaves of trees. They possess seven vertebrae in the neck (the usual number for a mammal). They also have slightly elongated forelegs, about 10% longer than their hind legs.

Modifications to the giraffe's structure have evolved, particularly to the circulatory system. A giraffe's heart, which can weigh up to 10 kg (24 lb), has to generate around double the normal blood pressure for a large mammal in order to maintain blood flow to the brain against gravity. 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 exactly the same way as a pilot's g-suit.^{[citation needed]}

Social structure, reproduction and sexuality

Female giraffes associate in groups of a dozen or so members, occasionally including a few younger males. Males tend to live in "bachelor" herds, with older males often leading solitary lives. 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 to detect estrus in a multi-step process known as the flehmen response.

Giraffe gestation lasts between 14 and 15 months, after which a single calf is born. The mother gives birth standing up and the embryonic sack actually bursts when the baby falls to the ground. Newborn giraffes are about 1.8 metres 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. While adult giraffes are too large to be attacked by most predators, the young can fall prey to lions, leopards, hyenas, and African 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 (Encyclopedia of Animals).

The males often engage in necking, which has been described as having various functions. One of these is combat. These battles can be fatal, but are more often less severe. The longer a neck is, and the heavier the head at the end of the neck, the greater force a giraffe will be 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 that the length of the neck may be a product of sexual selection.^[5]

Another function of necking is affectionate and sexual, in which two males will caress and court each other, leading up to mounting and climax. Same sex relations are more frequent than heterosexual behavior. In one area 94% of mounting incidents were of a homosexual nature. The proportion of same sex courtships varies between 30 and 75%, and at any given time one in twenty males will be engaged in affectionate necking behavior with another male. Females, on the other hand, only appear to have same sex relations in 1% of mounting incidents.^[6]

Other behavior

The giraffe browses on the twigs of trees, preferring plants of the Mimosa genus; but it appears that it can live without inconvenience on other vegetable food. A giraffe can eat 63 kg (140 lb) of leaves and twigs daily.

The pace of the giraffe is an amble, though when pursued it can run extremely fast. It can not sustain a lengthened 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.

The giraffe defends itself against threats by kicking with great force. A single well-placed kick of an adult giraffe can shatter a lion's skull or break its spine.

The giraffe has one of the shortest sleep requirement of any mammal, which is between 10 minutes and two hours in a 24-hour period. This has led to the myth that giraffes cannot lie down and that if they do so, they will die.

A giraffe will clean off any bugs that appear on its face with its extremely long tongue (about 18 inches/45 centimeter). The tongue is tough on account of the giraffe's diet, which includes thorns from the tree it is making a meal of. In Southern Africa, giraffes are partial to all acacias — especially Acacia erioloba — and possess a specially-adapted tongue and lips that appear to be immune to the vicious thorns.

Giraffes are thought to be mute; however, although generally quiet, they have been heard to grunt, snort and bleat and also recent research has shown evidence that the animal communicates at an infrasound level^[7].

The instinct of some other African animals is to stay close to the giraffe, for the giraffe's high vantage point can see predators from far away.^[8]

Evolutionary perspectives

The long neck allows a giraffe to eat from the tops of trees. However, since female giraffes are not as tall as male giraffes and tend to feed from much lower heights than their male counterparts, it is hard to say that they need the long necks purely for metabolic reasons. Furthermore, the additional length that helps a giraffe reach the top food sources makes it difficult for the same creature to drink. The ecological niche which at least male giraffes utilize is only used by a single other species, the African Elephant. It may be that the long neck originally evolved when the benefit of filling the ecological niche was more pronounced due to the presence of other, now extinct, giant ungulates in Africa. ^{[citation needed]}

It has been observed that males use their long necks not only for feeding, but also for combat and competition. Indeed, sexual dimorphism is strongly represented among giraffes, with females having shorter, lighter necks than males. A female's neck and head mass will level off after about ten years of age, while a male's will continue to increase throughout its twenty-plus years of life.

Giraffe subspecies

There are nine generally accepted subspecies, differentiated by color and pattern variations and range:

• Reticulated or Somali Giraffe (G.c. reticulata) — large, polygonal liver-colored 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 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 do cover the inner legs. Range: western and southwestern Sudan.
• Masai 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's or Baringo 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 or Rhodesian Giraffe (G.c. thornicrofti) — star-shaped or leafy spots extend to the lower leg. Range: eastern Zambia.
• West African or Nigerian Giraffe (G.c. peralta) — numerous pale, yellowish red spots. Range: Chad.

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.

Gallery

References

External links

• Giraffes: Wildlife summary from the African Wildlife Foundation
• ARKive - images and movies of the giraffe (Giraffa camelopardalis).
• Introduction to the history of the Giraffe in Middle Ages (French)
• Animal Diversity Web - Giraffa camelopardalis
• Giraffe Central web directory
• IUCN Red List of Threatened Species
• PBS Nature: Tall Blondes (Giraffes)
• Giraffe Pictures and Observations
• Nature-Wildlife
• Matt's World of Wicked Giraffes
• Over 80 Giraffe Cartoons
• Rare White Giraffe spotted in Africa
• Giraffe facts and photos - Wild Animals Online encyclopedia
• Mating System
• Giraffe Info Sheet
• Giraffe photos and information
• Long-term suppression of fertility in female giraffe using the GnRH agonist deslorelin as a long-acting implant