Monday, June 27, 2011

Zebra2


Classification

Zebras in Botswana
There are three extant species. Collectively, two of the species have eight subspecies (seven extant). Zebra populations are diverse, and the relationships between and the taxonomic status of several of the subspecies are not well known.
An albino zebra in captivity
The plains zebra (Equus quagga, formerly Equus burchelli) is the most common, and has or had about twelve subspecies distributed across much of southern and eastern Africa. It, or particular subspecies of it, have also been known as the common zebra, the dauw, Burchell's Zebra(actually the subspecies Equus quagga burchellii), Chapman's zebra, Wahlberg's zebra, Selous' zebra, Grant's zebra, Boehm's zebra and the quagga (another extinct subspecies, Equus quagga quagga).
The mountain zebra (Equus zebra) of southwest Africa tends to have a sleek coat with a white belly and narrower stripes than the plains Zebra. It has two subspecies and is classified as vulnerable.
Grévy's Zebra (Equus grevyi) is the largest type, with a long, narrow head, making it appear rathermule-like. It is an inhabitant of the semiarid grasslands of Ethiopia and northern Kenya. Grévy's zebra is the rarest species, and is classified as endangered.
Although zebra species may have overlapping ranges, they do not interbreed. This held true even when the quagga and Burchell's race of plains zebra shared the same area. In captivity, plains zebras have been crossed with mountain zebras. The hybrid foals lacked a dewlap and resembled the plains zebra apart from their larger ears and their hindquarters pattern. Attempts to breed a Grévy's zebra stallion to mountain zebra mares resulted in a high rate of miscarriage. In captivity, crosses between zebras and other (non-zebra) equines have produced several distinct hybrids, including the zebroid, zeedonk, zony, and zorse. In certain regions of Kenya, plains zebras and Grévy's Zebra coexist, and fertile hybrids occur.[6]

Physical attributes

Size and weight

The common plains zebra is about 50-52 inches (1.3 m) at the shoulder with a body ranging from 6-8.5 feet (2-2.6 m) long with an 18-inch (0.5 m) tail. It can weigh up to 770 pounds (350 kg), males being slightly bigger than females. Grévy's Zebra is considerably larger, while themountain zebra is somewhat smaller. [7]

Stripes

It was previously believed that zebras were white animals with black stripes, since some zebras have white underbellies. Embryological evidence, however, shows that the animal's background color is black and the white stripes and bellies are additions.[3]
A mother nursing her young blends into a stand of deadwood.
The stripes are typically vertical on the head, neck, forequarters, and main body, with horizontal stripes at the rear and on the legs of the animal. The "zebra crossing" is named after the zebra's black and white stripes.
A wide variety of hypotheses have been proposed to account for the evolution of the striking stripes of zebras. The more traditional of these (1 & 2, below) relate to camouflage.
1. The vertical striping may help the zebra hide in grass. While seeming absurd at first glance, considering that grass is neither white nor black, it is supposed to be effective against the zebra's main predator, the lion, which is color blind[dubious – discuss]. In addition, even at moderate distances, the striking striping merges to an apparent grey.
2. Another hypothesis is that since zebras are herd animals, the stripes may help to confuse predators - a number of zebras standing or moving close together may appear as one large animal, making it more difficult for the lion to pick out any single zebra to attack.[8][unreliable source?]
3. It has been suggested that the stripes serve as visual cues and identification.[3] Although each striping pattern is unique to each individual, it is not known whether zebras can recognize one another by their stripes.
4. One theory suggested by an innovative experiment posits that the disruptive colouration is an effective means of confusing the visual system of the blood-sucking tsetse fly.[9]
5. Alternative theories include that the stripes coincide with fat patterning beneath the skin, serving as a thermo-regulatory mechanism for the zebra, or that wounds sustained disrupt the striping pattern to clearly indicate the fitness of the animal to potential mates.
A zebra walking

Gaits

Like horses, zebras walk, trot, canter and gallop. They are generally slower than horses, but their great stamina helps them outpace predators. When chased, a zebra will zig-zag from side to side, making it more difficult for the predator. When cornered, the zebra will rear up and kick or bite its attacker.
Closeup of a zebra

Senses

Zebras have excellent eyesight. It is believed that they can see in color. Like most ungulates, the zebra has its eyes on the sides of its head, giving it a wide field of view. Zebras also have night vision, although not as advanced as that of most of their predators.
Zebras have excellent hearing, and tend to have larger, rounder ears than horses. Like horses and other ungulates, zebra can turn their ears in almost any direction. In addition to eyesight and hearing, zebras have an acute sense of smell and taste.

Ecology and behavior

Harems

Zebras in Tanzania
Like most members of the horse family, zebras are highly social. Their social structure, however, depends on the species. Mountain zebras and plains zebras live in groups, known as 'harems', consisting of one stallion with up to six mares and their foals. Bachelor males either live alone or with groups of other bachelors until they are old enough to challenge a breeding stallion. When attacked by packs of hyenas or wild dogs a zebra group will huddle together with the foals in the middle while the stallion tries to ward them off.
Unlike the other zebra species, Grevy's zebras do not have permanent social bonds. A group of these zebras rarely stays together for more than a few months. The foals stay with their mothers, while adult males live alone. Like the other two zebra species, bachelor male zebras will organize in groups.
Like horses, zebras sleep standing up, and only sleep when neighbors are around to warn them of predators.

Communication

A zebra feeding on grass
Zebras communicate with each other with high pitched barks and whinnying. Grevy's zebras make mule-like brays. A zebra’s ears signify its mood. When a zebra is in a calm, tense or friendly mood, its ears stand erect. When it is frightened, its ears are pushed forward. When angry, the ears are pulled backward. When surveying an area for predators, zebras will stand in an alert posture; with ears erect, head held high, and staring. When tense they will also snort. When a predator is spotted or sensed, a zebra will bark (or bray) loudly.
Mountain zebra -uenozoo2010.ogv
Hartmann's Mountain Zebra with aBarbary sheep behind it, in captivity at Ueno Zoo, in Japan. (video)

Food and foraging

Zebras feed almost entirely on grasses, but may occasionally eat shrubs, herbs, twigs, leaves and bark. Their digestive systems allow them to subsist on diets of lower nutritional quality than that necessary for other herbivores.

Reproduction

Female zebras mature earlier than the males, and a mare may have her first foal by the age of three. Males are not able to breed until the age of five or six. Mares may give birth to one foal every twelve months. She nurses the foal for up to a year. Like horses, zebras are able to stand, walk and suckle shortly after they are born. A zebra foal is brown and white instead of black and white at birth.
Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grevy’s zebra foals have only their mother as a regular protector, since, as noted above, Grevy's zebra groups often disband after a few months.

Human interactions

Lord Rothschild with his famed zebra carriage (sp. Equus quagga burchellii), which he frequently drove through London

Domestication

Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. Most of these attempts failed, though, due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between any species of zebra and a horse, pony, donkey or ass) are preferred over purebred zebras.
In England, the zoological collector Lord Rothschild frequently used zebras to draw a carriage. In 1907, Rosendo Ribeiro, the first doctor in Nairobi, Kenya, used a riding zebra for house calls. In the mid-19th century, Governor George Grey imported zebras to New Zealand from his previous posting in South Africa, and used them to pull his carriage on his privately owned Kawau Island.
A tamed zebra being ridden in East Africa
Captain Horace Hayes, in "Points of the Horse" (circa 1893), compared the usefulness of different zebra species. In 1891, Hayes broke a mature, intact mountain zebra stallion to ride in two days time, and the animal was quiet enough for his wife to ride and be photographed upon. He found the Burchell's zebra easy to break, and considered it ideal for domestication, as it was immune to the bite of the tsetse fly. He considered the quagga (now extinct) well-suited to domestication due to being easy to train to saddle and harness.[10]

Conservation

Modern man has had great impact on the zebra population. Zebras were, and still are, hunted for their skins, and for meat. They also compete with livestock for forage,[11] and sometimes culled.
The Cape mountain zebra was hunted to near extinction, with less than 100 individuals by the 1930s. The population has increased to about 700 due to conservation efforts, though. Both mountain zebra subspecies are currently protected in national parks, but are still endangered.
Zebras on the Botswana coat of arms.
The Grevy's zebra is also endangered. Hunting and competition from livestock have greatly decreased their population. Because of the population's small size, environmental hazards, such as drought, are capable of affecting the entire species. Plains zebras are much more numerous and have a healthy population. Nevertheless, they too have been reduced by hunting and loss of habitat to farming. One subspecies, the quagga, is now extinct.

Cultural depictions

Zebras have been the subject of African folk tales which tell how they got their stripes. According to a Bushmen folk tale of Namibia, the zebra was once all white, but acquired its black stripes after a fight with a baboon over a waterhole. After kicking the baboon so hard, the zebra lost his balance and tripped over a fire, and the fire sticks left scorch marks all over his white coat.[12] In the film Fantasia, two centaurs are depicted being half human and half zebra, instead of the typical half human and half horse.[13]
Illustration of a zebra by Ludolphus
Zebra are a popular subject in art.[14] The fourth Mughal emperor Jahangir (r.1605-24), commissioned a painting of the zebra, which was completed by Ustad Mansur.[15] Zebra stripes are also a popular style for furniture, carpets and fashion.
When depicted in movies and cartoons, zebras are most often miscellaneous characters, but have had some starring roles, notably in Madagascar and Racing Stripes. Zebras also serve as mascots and symbols for products and corporations, notably Zebra Technologies and Fruit Stripegum. Zebras are featured on the coat of arms of Botswana.

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