Zebra
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| Zebra | ||||||||||||||
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Equus quagga boehmi | ||||||||||||||
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| Equus zebra |
The Zebra is a part of the horse family, Equidae, native to central, eastern and southern Africa. They are most well known for their distinctive black and white stripes. The pronunciation is (IPA): /ˈziːbrə/ (ZEE-bra) in North America or (IPA): /ˈzɛbrə/ (ZEB-ra) in the United Kingdom.
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[edit] Evolution
Zebras were the second species to diverge from the earliest proto-horses, after the asses, around 4 million years ago. The Grevy's zebra is believed to have been the first zebra species to emerge. Zebras might have lived in North America in prehistoric times. Fossils of an ancient horselike animal were discovered in the Hagerman Fossil Beds National Monument in Hagerman, Idaho. It was named the Hagerman Horse with a scientific name of Equus simplicidens. There is some debate among paleontologists on whether the animal was a horse or a bona-fide zebra. While the animal's overall anatomy seems to be more horselike, its skull and teeth indicate that it was more closely related to the Grevy's Zebra. Thus it is also called the American zebra or Hagerman Zebra.[1]
[edit] Physical attributes
[edit] Stripes
Zebras are black with white stripes and their bellies have a large white blotch for camouflage purposes.[2] The reasons is it believed that that zebras are black with white stripes are: (1) white horses would not survive well in the African plains or forests; (2) The quagga, a extinct zebra species, had the zebra striping pattern in the front of the animal, but had a dark rump; (3) when the region between the pigmented bands becomes too wide, secondary stripes emerge, as if suppression was weakening. The fact that zebras have white bellies is not very strong evidence for a white background, since many animals of different colors have white or light colored bellies.
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 white and black stripes.
Zoologists believe that the stripes act as a camouflage mechanism. This is accomplished in several ways. First, the vertical striping helps 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. Theoretically a zebra standing still in tall grass may not be noticed at all by a lion. Additionally, 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.[3] A herd of zebras scattering to avoid a predator will also represent to that predator a confused mass of vertical stripes travelling in multiple directions making it difficult for the predator to track an individual visually as it separates from its herdmates, although biologists have never observed lions appearing confused by zebra stripes.
Stripes are also believed to play a role in social interactions, with slight variations of the pattern allowing the animals to distinguish between individuals.
A more recent theory, supported by experiment, posits that the disruptive coloration is also an effective means of confusing the visual system of the blood-sucking tsetse fly.[4] Alternative theories include that the stripes coincide with fat patterning beneath the skin, serving as a thermoregulatory mechanism for the zebra, and that wounds sustained disrupt the striping pattern to clearly indicate the fitness of the animal to potential mates.
[edit] Gaits
Like horses, zebras walk, trot, canter and gallop. They are generally slower than horses but their great stamina helps them outpace predators; especially lions who get tired rather quickly. 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 its attacker. A kick from a zebra can be fatal. Zebras will bite their attackers as well.
[edit] Eyesight
Zebras have excellent eyesight with binocular-like vision. 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 it's not as advanced as that of most of their predators.
[edit] Ears and hearing
Zebras have great hearing, and tend to have larger and rounder ears than horses. Like horses and other ungulates, zebra can turn their ears in almost any direction toward and listen for sounds. Zebra ear movement can also signify the zebra's mood. When a zebra is in a calm or friendly mood, its ears stand erect. When it is frightened, its ears are pulled forward. When angry, the ears are pulled backward.
[edit] Other senses
In addition to eyesight and hearing, zebra have an acute sense of smell and taste.
[edit] Ecology
[edit] Social behavior
Like most horses, zebras are highly sociable. Their social structure, however, depends on the species. Mountain zebras and Plains zebras live in groups consisting of one stallion with up to six mares and their foals. The stallion defends his group from bachelor males. When challenged, the stallion would issue a warning to the invader by rubbing nose or shoulder with him. If the warning is not heeded, a fight breaks out. Zebra fights often become very violent, with the animals biting at each other's necks or legs and kicking. While stallions may come and go, the mares stay together for life. They exist in a hierarchy with the alpha female being the first to mate with the stallion and being the one to lead the group.
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 mother, while the adult male lives alone.
Like horses, zebras sleep standing up and only sleep when neighbors are around to warn them of predators. When attacked by packs of hyenas or wild dogs, a Plains zebra group will huddle together wih the foals in the middle while the stallion tries to ward them off. Zebra groups often come together in large herds and migrate together along with other species such as Blue wildebeests. Zebras communicate with each other with high-pitched barks and brays.
[edit] Food and foraging
Zebras are very adaptable grazers. They feed mainly on grasses but will also eat shrubs, herbs, twigs, leaves and bark. Plains zebras are pioneer grazers and are the first to eat at well-vegetated area. After the area is mowed down by the zebras, other grazers follow.
[edit] Reproduction
Like most animal species, 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, zebra are able to stand and walk shortly after they're born. A zebra foal is brown and white instead of black and white at birth. Plains and Mountain zebra foals are protected by their mother as well as the head stallion and the other mares in their group. Grevy’s zebra foals have only their mother. Even with parental protection up to 50% of zebra foals are taken by predation, disease and starvation each year.
[edit] Species
There are four extant species, as well as several subspecies. Zebra populations vary a great deal, and the relationships between and the taxonomic status of several of the subspecies are well known.
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 burchelli), 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 endangered.
Grevy's Zebra (Equus grevyi) is the largest type, with an erect mane, and a long, narrow head making it appear rather mule-like. It is an inhabitant of the semi-arid grasslands of Ethiopia and northern Kenya. The Grevy's Zebra is one of the rarest species of zebra around today, 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. According to Dorcas McClintock in "A Natural History Of Zebras," Grevy's zebra has 46 chromosomes; plains zebras have 44 chromosomes and mountain zebras have 32 chromosomes. 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 Grevy's zebra stallion to Mountain Zebra mares resulted in a high rate of miscarriage.
[edit] Zebra classification
- Plains Zebra, Equus quagga
- Quagga, Equus quagga quagga (extinct)
- Burchell's Zebra, Equus quagga burchellii (includes Damara Zebra)
- Grant's Zebra, Equus quagga boehmi
- Selous' zebra, Equus quagga borensis
- Chapman's Zebra, Equus quagga chapmani
- Crawshay's Zebra, Equus quagga crawshayi
- Cape Mountain Zebra, Equus zebra
- Hartmann's Mountain Zebra, Equus hartmannae
- Grevy's Zebra, Equus grevyi
For the remaining species of the genus and family see Equidae.
[edit] Domestication
Attempts have been made to train zebras for riding since they have better resistance than horses to African diseases. However most of these attempts failed, due to the zebra's 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 pure-bred 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.
Captain Horace Hayes, in "Points of the Horse" (circa 1899) compared the usefulness of different zebra species. Hayes saddled and bridled a Mountain Zebra in less than one hour, but was unable to give it a "mouth" during the two days it was in his possession. He noted that the zebra's neck was so stiff and strong that he was unable to bend it in any direction. Although he taught it to do what he wanted in a circus ring, when he took it outdoors he was unable to control it. He found the Burchell's Zebra easy to break in and considered it ideal for domestication, as it was also immune to the bite of the tsetse fly. He considered the quagga well-suited to domestication due to being stronger, more docile and more horse-like than other zebras.