Giraffe
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? Giraffe Conservation status: Lower
risk
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| Giraffa
camelopardalis Linnaeus, 1758 |
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The Giraffe (Giraffa camelopardalis) is an 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 900 kilograms (2000 pounds). Females are generally slightly shorter and weigh less.
Native to Africa, 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.
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 (and perhaps being a hybrid of the two) [1].
Giraffe Subspecies
There are nine generally accepted subspecies, differentiated by colour 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 sources combine Kordofan and West African, Nubian and Rothschild's, and Angolan and Southern African giraffes, respectively, into single subspecies. Four other subspecies have been described, but are not widely agreed upon: Cape Giraffe (G.c. capensis), Lado Giraffe (G.c. cottoni), Congo Giraffe (G.c. congoensis), and Transvaal Giraffe (G.c. wardi). Some scientists go so far as to group all populations except the Masai into a single subspecies.
Characteristics
Giraffes are famous for their long necks which allow them to browse on the leaves of trees, and elongated forelegs (which appear much longer than the hind legs, but in reality, are only 1/10th longer). The bony structure of the neck is essentially unchanged from that of other mammals: there are no extra vertebrae, but each of the seven bones is greatly enlarged. Bone constitutes the bud-like horns called ossicorns, which are covered with the Giraffe's skin like the rest of the skull.
Modifications to the Giraffe's structure have evolved, particularly to the circulatory system. A giraffe's heart, which can weigh up to 24 lb (10 kg), 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.
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 calf that may be a week old already; 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 Hunting Dogs. It has been speculated that their characteristic spotted pattern provides a certain degree of camouflage. Only 25 to 50 percent of Giraffe calves reach adulthood; those that do have a life expectancy of between 20 and 25 years in the wild and 28 years in captivity (Encyclopedia of Animals).
In its native country the Giraffe browses on the twigs of trees, preferring plants of the Mimosa genus; but it appears that it can without inconvenience live on other vegetable food. A Giraffe can eat 63 kilograms (140 pounds) of leaves and twigs daily.
The pace of the Giraffe is an amble, though when pursued it can run extremely fast. However, the small size of its lungs prevents it from supporting a lengthened chase.
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 reckoned to be between 20 minutes and two hours in a 24 hour period.
A Giraffe will clean off any bugs that appear on its face (usually while eating) with its extremely long tongue (about 18 inches). The tongue is unusually tough on account of the giraffe's diet, which often consists of thorns from the tree it is making a meal of.
Giraffes are thought to be
mute. However, recent research has shown evidence that the animal communicates at an
infrasound level with a surprising level of
complexity.
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, including
Spanish retain it. The Arabic word الزرافة
ziraafa or
zurapha (undoubtedly of African origin), was used in English from the sixteenth century on, often in an Italianate form
Giraffa.
Evolutionary perspectives
There can be no doubt that the neck and forelegs of the giraffe are long relative to the proportions found in almost all other ungulates. What cannot be said with any good certainty however, is exactly why this is the case. We can, however, observe the behaviour of modern giraffes and infer why they may have such long necks.
The long necks do allow a giraffe to eat from the tops of trees. However, since female giraffes are not as high 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 for metabolic reasons. Furthermore, the additional length that helps a giraffe reach the top food sources makes it incredibly difficult for the same creature to drink. While the ecological niche which at least male giraffes utilize is only used by a single other species, the African Elephant, there has been no selective forces to maintain the length of the giraffe's neck for a long time. 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 giant ungulates in Africa, which are now extinct. Today, the maintenance of the giraffe's neck length is more an example of neutralist selection than of "survival of the fittest".
In addition to the remarkably long neck, giraffes have enlarged forelegs. These legs make it possible for giraffes to move swiftly and defend themselves against predators. It is unknown whether or not the size of the giraffe's neck, working in combination with the leg length, may provide a biomechanical advantage in defending against lion attacks.
Finally, it has been observed that males use their long necks, not just for feeding, but for combat and competition. Indeed, sexual dimorphism is strongly represented among giraffes with females having shorter, lighter necks than males. Among females, the neck and head mass levels off after about ten years of age, while the same organs in males will continue to grow throughout the twenty-plus year lifetime. The males engage in necking 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. In following the logic of sexual selection, it is thus very possible that the giraffe's long neck may be a result of competition among males and female preferences.