Subspecies include the extinct quagga and six recognized extant subspecies, though there is great variation in coat patterns between individuals. The striping pattern is unique among ungulates in the region, and its functions are disputed. Suggested functions include crypsis, forms of motion camouflage, social signaling and recognition, and discouraging biting flies.
The plains zebra's range is fragmented, but spans much of southern and eastern Africa south of the Sahara. Its habitat is generally but not exclusively treeless grasslands and savanna woodlands, both tropical and temperate. They generally avoid desert, dense rainforest and permanent wetlands, and rarely stray more than 30 kilometers from a water source.
The plains zebra is a highly social species, forming harems with a single stallion, several mares and their recent offspring; there are also bachelor groups. Groups may come together to form herds. The animals keep watch for predators rather than attempting to hide; they bark or snort when they see a predator, and the harem stallion attacks predators such as dogs, hyenas and leopards to defend his harem. The species population is stable and not endangered, though some populations such as in Tanzania have declined sharply.
Taxonomy
There is a dispute among biologists as to how to properly classify the various species of zebra. It is thought that the plains zebra and mountain zebra belong to the subgenus Hippotigris and that Grévy's zebra is the sole species of subgenus Dolichohippus. This is on account of Grévy's zebra resembling an ass (subgenus Asinus), while the plains zebra and mountain zebra are more horse-like. All three animals belong to the genus Equus along with other living equids. However, recent phylogenetic evidence suggests that the mountain zebras and Grévy's zebras should be classified with asses and donkeys in a lineage separate from the plains zebra.[3] In areas where plains zebras are sympatric with Grévy's zebras, it is not unusual to find them in the same herds[4] and fertile hybrids occur.[5] 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.Subspecies
- Quagga, †Equus quagga quagga – Boddaert, 1785
- Burchell's zebra, Equus quagga burchellii – Gray, 1824
- Grant's zebra, Equus quagga boehmi – Matschie, 1892
- Maneless zebra Equus quagga borensis – Lönnberg, 1921
- Chapman's zebra, Equus quagga chapmani – Layard, 1865
- Crawshay's zebra, Equus quagga crawshayi – De Winton, 1896
- Selous' zebra, Equus quagga selousi - Pocock 1897
Burchell's zebra was thought to have been hunted to extinction. However, Groves and Bell concluded in their 2004 publication that "the extinct true Burchell's zebra" is a phantom. Careful study of the original zebra populations in Zululand and Swaziland, and of skins harvested on game farms in Zululand and Natal, has revealed that a certain small proportion shows similarity to what now is regarded as typical "burchellii". The type localities of the subspecies Equus quagga burchellii and Equus quagga antiquorum (the Damara zebra) are so close to each other that the two are in fact one, and that therefore the older of the two names should take precedence over the younger. They therefore say that the correct name for the southernmost subspecies must be burchellii not antiquorum. The subspecies Equus quagga burchellii still exists in KwaZulu-Natal and in Etosha.
Physical description
Like all zebras, they are boldly striped in black and white, and no two individuals look exactly alike. They also have black or dark muzzles. The natal coat of a foal is brown and white. All have vertical stripes on the forepart of the body, which tend towards the horizontal on the hindquarters. The northern populations have narrower and more defined striping;[8][9] southern populations have varied but lesser amounts of striping on the underparts, the legs and the hindquarters.[8] Southern populations also have brown "shadow" stripes between the black and white coloring.[8][9] These are absent or poorly expressed in northern zebras.[8][9]
Embryological evidence has shown that the zebra's background color is dark and the white is an addition.[10] The first subspecies to be described, the now-extinct quagga, had plain brown hindquarters. There have been various mutations of the zebra's pelage, from mostly white to mostly black.[11] Rare albino zebras have been recorded in the forests of Mount Kenya.[12]
Function of the stripes
Perhaps the best explanation for the stripes is that they serve a social function.[10] Individual zebras can apparently recognize each other by their striping patterns.[15] The stripes may also serve as visual cues for grooming.[10] In addition, they could serve to help zebra groups stay together when they are fleeing.[13] A 2012 study suggests that stripes may have developed to discourage biting flies. Experiments have demonstrated that the stripes polarize light in such a way that it discourages tabanids (biting flies) in a manner not shown with other coat patterns.[16] Another study from 2015 determined that environment temperature is a strong predictor for zebra striping patterns and proposed that the stripes may be related to thermoregulation.[17]
Ecology
Range and habitat
Plains zebras generally live in treeless grasslands and savanna woodlands[9] but can be found in a variety of habitats, both tropical and temperate. However they are generally absent from deserts, dense rainforests and permanent wetlands.[9] Zebras also live in elevations from sea level to 4,300 m on Mount Kenya. They rely on rainfall for food and water, and go on great migrations to follow the rains. The zebras will migrate up to 700 miles (1,100 km) for food. Other grazers also migrate. Plains zebras are highly water-dependent[4] and are usually found within 25–30 kilometers of a water source.
Diet and predation
The plains zebra's major predators are lions and spotted hyenas.[8] Nile crocodiles are also great threats during migratory river crossings. Wild dogs, cheetahs, and leopards also prey on zebras, although the threats they pose are generally minor and they mostly attack the foals. Olive Baboons may prey on foals, but pose no threat to adults. The zebra can be a formidable adversary, since they have a strong bite and a kick powerful enough to kill land predators. They often try to outrun larger predators such as lions and spotted hyenas, whereas they often stand their ground with the smaller predators.
Interactions with other grazers
Plains zebra herds will mix and migrate together along with other species such as wildebeests. Wildebeests and zebras generally coexist peacefully and will alert each other to predators. However, aggressive interactions occasionally occur.[21][22]Behavior
Social structure
Stallions form and expand their harems by abducting young mares from their natal harems.[4][24] When a mare reaches sexual maturity, she will exhibit the estrous posture, which attracts nearby stallions,[24] both bachelors and harem leaders. Her family stallion (likely her father) will chase off or fight stallions attempting to abduct her. Even after a young mare is isolated from her natal harem, the fight over her continues until her estrous cycle is over, and it starts again with the next estrous cycle.[25] It is rare that the mare's original abductor keeps her for long.[25] When the mare finally ovulates, the male that impregnates her keeps her for good. Thus, the mare becomes a permanent member of a new harem.[25][26] The estrous posture of a female becomes less noticeable to outside males as she gets older, hence competition for older females is virtually non-existent.[15]
A stallion will defend his group from other males. When challenged, the stallion issues 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, heads or legs, wrestling to the ground, and occasional kicking. Sometimes a stallion will lie still on the ground as if surrendering, but once the other male lets up, will strike and continue the fight.[4] Most fighting occurs over young mares in estrus, and as long as a harem stallion is healthy, he will usually not be challenged. Only unhealthy stallions have their harems taken over, and even then the new stallion gradually takes over pushing the old one out without a fight.[4]
Communication
At least six different calls have been documented for the plains zebra. One of which is its distinctive high-pitched contact call heard as "a-ha, a-ha, a-ha" or "kwa-ha, kaw-ha, ha, ha".[15] When a predator is sighted, a zebra will make a two-syllable alarm call. A loud snort is made when moving in cover of potential danger. When in contentment, a zebra will make a more drawn-out snort. Males will make a short high-pitched squeal when hurt and foals will emit a drawn out wail when in distress.[15] There are two main facial expressions made by zebras. One is for greeting and involves the ears sticking up and directed forward; the other is threatening and involves the ears down.[15]
Reproduction
Young male zebras eventually leave their family groups. This is not because of sexual maturity or being kicked out by their fathers, but because their relationship with their mothers have faded after the birth of a sibling.[8][24] The young stallion then seeks out other young stallions for company.[24] Young females may stay in the harem until they are abducted by another stallion.[8]
Anti-predator behavior
For protection from land predators, the plains zebra retreats into open areas with good visibility at night. When the groups forage or sleep, one zebra will keep watch, and if a predator is spotted, it will bark or snort loudly.[8] When being hunted by hyenas or wild dogs, a zebra harem stays close together and cooperates to protect threatened members,[4] particularly the young. The harem stallion will go on the offensive and attack the dogs or hyenas.[4] Though hyenas may harass the stallion, they usually only concentrate on the herd, and attempt to dodge the stallion's assaults. Unlike stallions, mares typically only react aggressively to hyenas or dogs when their foals are threatened. Unlike wildebeest, zebras rarely take to water when escaping hyenas.[29] With lions, a zebra's best defense is to outpace them, as lions do not have as much endurance as hyenas or wild dogs. Cheetahs and leopards are mostly threats to foals, as an adult zebra is fully capable of driving them away.
Human interactions
Conservation
Overall, the plains zebra population remains stable, and the species faces no major threat that would cause range-wide decline.[1] The zebra can be found in numerous protected areas across its range, including the Serengeti National Park in Tanzania, Tsavo and Masai Mara in Kenya, Hwange National Park in Zimbabwe, Etosha National Park in Namibia, and Kruger National Park in South Africa. There are some stable populations in unprotected areas.[1]
Nevertheless, plains zebras are protected in most of their range. They are an important economic source in tourism.