Zebras (US: /ˈziːbrəz/, UK: /ˈzɛbrəz, ˈziː-/)[1] (subgenus Hippotigris) are African equines with distinctive black-and-white striped coats. There are three living species: the Grévy's zebra (Equus grevyi), plains zebra (E. quagga), and the mountain zebra (E. zebra). Zebras share the genus Equus with horses and asses, the three groups being the only living members of the family Equidae. Zebra stripes come in different patterns, unique to each individual. Several theories have been proposed for the function of these stripes, with most evidence supporting them as a deterrent for biting flies. Zebras inhabit eastern and southern Africa and can be found in a variety of habitats such as savannahs, grasslands, woodlands, shrublands, and mountainous areas.
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Zebras are primarily grazers and can subsist on lower-quality vegetation. They are preyed on mainly by lions, and typically flee when threatened but also bite and kick. Zebra species differ in social behaviour, with plains and mountain zebra living in stable harems consisting of an adult male or stallion, several adult females or mares, and their young or foals; while Grévy's zebra live alone or in loosely associated herds. In harem-holding species, adult females mate only with their harem stallion, while male Grévy's zebras establish territories which attract females and the species is promiscuous. Zebras communicate with various vocalisations, body postures and facial expressions. Social grooming strengthens social bonds in plains and mountain zebras.
Zebras' dazzling stripes make them among the most recognisable mammals. They have been featured in art and stories in Africa and beyond. Historically, they have been highly sought after by exotic animal collectors, but unlike horses and donkeys, zebras have never been truly domesticated. The International Union for Conservation of Nature (IUCN) lists the Grévy's zebra as endangered, the mountain zebra as vulnerable and the plains zebra as near-threatened. The quagga (E. quagga quagga), a type of plains zebra, was driven to extinction in the 19th century. Nevertheless, zebras can be found in numerous protected areas.
The English name "zebra" derives from Italian, Spanish or Portuguese.[2][3] Its origins may lie in the Latin equiferus, meaning "wild horse". Equiferus appears to have entered into Portuguese as ezebro or zebro, which was originally used for a legendary equine in the wilds of the Iberian Peninsula during the Middle Ages. In 1591, Italian explorer Filippo Pigafetta recorded "zebra" being used to refer to the African animals by Portuguese visitors to the continent.[4] In ancient times, the African zebra was called hippotigris ("horse tiger") by the Greeks and Romans.[4][5]
The word "zebra" was traditionally pronounced with a long initial vowel, but over the course of the 20th century the pronunciation with the short initial vowel became the norm in the UK and the Commonwealth.[6] The pronunciation with a long initial vowel remains standard in US English.[7]
Zebras are classified in the genus Equus (known as equines) along with horses and asses. These three groups are the only living members of the family Equidae.[8] The plains zebra and mountain zebra were traditionally placed in the subgenus Hippotigris (C. H. Smith, 1841) in contrast to the Grévy's zebra which was considered the sole species of subgenus Dolichohippus (Heller, 1912).[9][10][11] Groves and Bell (2004) placed all three species in the subgenus Hippotigris.[12] A 2013 phylogenetic study found that the plains zebra is more closely related to Grévy's zebras than mountain zebras.[13] The extinct quagga was originally classified as a distinct species.[14] Later genetic studies have placed it as the same species as the plains zebra, either a subspecies or just the southernmost population.[15][16] Molecular evidence supports zebras as a monophyletic lineage.[13][17][18]
In addition to the three living species, some fossil zebras and relatives have also been identified. Equus koobiforensis is an early equine basal to zebras found in the Shungura Formation, Ethiopia and the Olduvai Gorge, Tanzania, and dated to around 2.3 mya.[33] E. oldowayensis is identified from remains in Olduvai Gorge dating to 1.8 mya.[34] Fossil skulls of E. mauritanicus from Algeria which date to around 1 mya appears to show affinities with the plains zebra.[35][36] E. capensis, known as the Cape zebra, appeared around 2 mya and lived throughout southern and eastern Africa.[37][34]
Non-African equines that may have been basal to zebras include E. sansaniensis of Eurasia (circa 2.5 mya) and E. namadicus (circa 2.5 mya) and E. sivalensis (circa 2.0 mya) of the Indian subcontinent.[33] A 2017 mitochondrial DNA study placed the Eurasian E. ovodovi and the subgenus Sussemionus lineage as closer to zebras than to asses.[38]
Fertile hybrids have been reported in the wild between plains and Grévy's zebra.[39] Hybridisation has also been recorded between the plains and mountain zebra, though it is possible that these are infertile due to the difference in chromosome numbers between the two species.[40] Captive zebras have been bred with horses and donkeys; these are known as zebroids. A zorse is a cross between a zebra and a horse; a zonkey between a zebra and a donkey and a zoni between a zebra and a pony. Zebroids are often born sterile with dwarfism.[41]
As with all wild equines, zebra have barrel-chested bodies with tufted tails, elongated faces and long necks with long, erect manes. Their thin legs are each supported by a spade-shaped toe covered in a hard hoof. Their dentition is adapted for grazing; they have large incisors that clip grass blades and rough molars and premolars well suited for grinding. Males have spade-shaped canines, which can be used as weapons in fighting. The eyes of zebras are at the sides and far up the head, which allows them to look over the tall grass while feeding. Their moderately long, erect ears are movable and can locate the source of a sound.[8][26][32]
Unlike horses, zebras and asses have chestnut callosities present only on their front legs. In contrast to other living equines, zebra have longer front legs than back legs.[32] Diagnostic traits of the zebra skull include: its relatively small size with a straight profile, more projected eye sockets, narrower rostrum, reduced postorbital bar, separation of the metaconid and metastylid of the tooth by a V-shaped canal and rounded enamel wall.[42]
Striping patterns are unique to an individual and heritable.[46] During embryonic development, the stripes appear at eight months, but the patterns may be determined at three to five weeks. For each species there is a point in embryonic development where the stripes are perpendicular to the dorsal line and spaced 0.4 mm (0.016 in) apart. However, this happens at three weeks of development for the plains zebra, four weeks for the mountain zebra, and five for Grévy's zebra. The difference in timing is thought to be responsible for the differences in the striping patterns of the different species.[43]
Various abnormalities of the patterns have been documented in plains zebras. In melanistic zebras, dark stripes are highly concentrated on the torso but the legs are whiter. "Spotted" individuals have broken up black stripes around the dorsal area.[47] There have even been morphs with white spots on dark backgrounds.[48] Striping abnormalities have been linked to inbreeding.[47] Albino zebras have been recorded in the forests of Mount Kenya, with the dark stripes being blonde.[49] The quagga had brown and white stripes on the head and neck, brown upper parts and a white belly, tail and legs.[50]
Zebras are preyed on mainly by lions. Leopards, cheetahs, spotted hyenas, brown hyenas and wild dogs pose less of a threat to adults.[82] Nile crocodiles also prey on zebras when they near water.[83] Biting and kicking are a zebra's defense tactics. When threatened by lions, zebras flee, and when caught they are rarely effective in fighting off the big cats.[84] In one study, the maximum speed of a zebra was found to be 50 km/h (31 mph) while a lion was measured at 74 km/h (46 mph). Zebras do not escape lions by speed alone but by sideways turning, especially when the cat is close behind.[85] With smaller predators like hyenas and dogs, zebras may act more aggressively, especially in defense of their young.[86]
Zebra species have two basic social structures. Plains and mountain zebras live in stable, closed family groups or harems consisting of one stallion, several mares, and their offspring. These groups have their own home ranges, which overlap, and they tend to be nomadic. Stallions form and expand their harems by recruiting young mares from their natal (birth) harems. The stability of the group remains even when the family stallion is displaced. Plains zebras groups gather into large herds and may create temporarily stable subgroups within a herd, allowing individuals to interact with those outside their group. Females in harems can spend more time feeding, and gain protection both for them and their young. The females have a linear dominance hierarchy with the high-ranking females being the ones that have lived in the group longest. While traveling, the most dominant females and their offspring lead the group, followed by the next most dominant. The family stallion trails behind. Young of both sexes leave their natal groups as they mature; females are usually herded by outside males to become part of their harems.[8][26][87]
In the more arid-living Grévy's zebras, adults have more fluid associations and adult males establish large territories, marked by dung piles, and mate with the females that enter them.[26][8] Grazing and drinking areas tend to be separated in these environments and the most dominant males establish territories near watering holes, which attract females with dependent foals and those who simply want a drink, while less dominant males control territories away from water with more vegetation, and only attract mares without foals.[88] Mares may travel through several territories but remain in one when they have young. Staying in a territory offers a female protection from harassment by outside males, as well as access to resources.[87][89] 2ff7e9595c
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