Zebra

• 1. Introduction

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  Charles Darwin once wrote that "a female zebra would not admit the addresses of a male ass until he was painted so as to resemble a zebra." He wrote that in 1871, and it shows how much attention the animal's coat drew from naturalists.

  Zebras are striped equines of eastern and southern Africa. They live in savannahs, grasslands, woodlands, shrublands and mountainous country.

  Why would any animal wear such a bold pattern, and what is that pattern actually doing for it? How do zebras organise their days, their families and their fights? And what happened when people set out to capture, tame, hunt and celebrate them?

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• 2. Names and Ancestry

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  The Greeks and Romans called the animal hippotigris, which means "horse tiger." The modern word arrived by a stranger route. In 1591, the Italian explorer Filippo Pigafetta recorded Portuguese visitors to Africa using "zebra" for the striped animals they met there. Its roots may lie in the Latin equiferus, meaning "wild horse." That term appears to have become ezebro or zebro in Portuguese, where it named a mysterious equine reported in the wilds of medieval Iberia.

  The 20th century split English speakers over how to say the word. Americans keep the long first vowel, while British speakers gradually settled on the short one.

  Grévy's zebra, the plains zebra and the mountain zebra are the three living species. They share the genus Equus with horses and asses, and these three groups are the only living members of the family Equidae.

  Their shared history began in North America. A 700,000-year-old horse bone from Canada, sequenced directly, implies that all equines had a common ancestor about 4.07 million years ago. The plausible range runs from 4.0 to 4.5 million years. Horses split away around that time, and equines then spread into Eurasia and Africa roughly 2.1-3.4 million years ago. Zebras and asses parted ways close to 2 million years ago. The mountain zebra branched off about 1.6 million years ago, and the plains and Grévy's zebras separated 1.4 million years ago.

  A 2013 study found the plains zebra to be closer kin to Grévy's zebra than to the mountain zebra. The quagga, now extinct, was first classed as a species of its own. Later genetic studies fold it into the plains zebra, either as a subspecies or as that animal's southernmost population.

  Olduvai Gorge holds remains of a fossil relative called E. oldowayensis, dating to 1.8 million years ago. Fossil skulls of E. mauritanicus from Algeria, about 1 million years old, show affinities with the plains zebra. The Cape zebra, E. capensis, appeared around 2 million years ago and ranged across southern and eastern Africa.

  Grévy's zebras carry 46 chromosomes, plains zebras 44 and mountain zebras 32. Fertile hybrids between plains and Grévy's zebras have been reported in the wild. Plains and mountain zebras have also crossed, though the difference in chromosome number may leave those offspring infertile.

  Captive zebras bred with horses and donkeys produce animals called zebroids. A zorse has a horse for its other parent, a zonkey a donkey, and a zoni a pony. Zebroids are often born sterile and with dwarfism.

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• 3. Stripes Up Close

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  Beneath the stripes, a zebra's skin is black. The belly and legs, where stripes are absent, show that the hair itself is white. Foals are born brown and white, and the brown darkens with age.

  A dorsal stripe works as the backbone for vertical stripes that run along the sides from head to rump. On the snout, the stripes curve toward the nostrils. Above the front legs they split into two branches. The stripes on the legs, ears and tail are separate and horizontal, while the rump carries a pattern specific to each species.

  Grévy's zebra has narrow stripes with concentric rings on the rump, a white belly and a white line around its ashy muzzle. The plains zebra has broad stripes that run horizontally across the rump. Northern plains populations are more extensively striped, while southern ones have whiter legs and bellies. The mountain zebra has stripes of intermediate width, a gridiron pattern on the rump and a black muzzle lined with chestnut or orange.

  A Grévy's zebra stands 125-160 cm at the shoulder and weighs 352-450 kg. A plains zebra stands 110-145 cm and weighs 175-385 kg. A mountain zebra stands 116-146 cm and weighs 204-430 kg.

  The stripes become visible eight months into development, but the pattern may be settled at only three to five weeks. Each pattern is unique to the individual and heritable. At one stage, every species passes through a point where the stripes run perpendicular to the dorsal line and sit 0.4 mm apart. That point arrives at three weeks in the plains zebra, four weeks in the mountain zebra and five weeks in Grévy's zebra. The difference in timing is thought to explain why the species look different.

  Unlike other living equines, zebras have front legs that are longer than their back legs. Their eyes sit at the sides and high on the head, which lets them look over tall grass while feeding. Large incisors clip grass blades, and rough molars grind them. Males carry spade-shaped canines that serve as weapons in fights.

  In plains zebras, observers have documented "melanistic" animals whose dark stripes crowd the torso while the legs stay whiter. "Spotted" individuals have black stripes broken up around the back, and some morphs show white spots on a dark background. Inbreeding has been linked to these abnormalities. Albino zebras recorded in the forests of Mount Kenya had blonde stripes. The extinct quagga had brown and white stripes on the head and neck, a brown upper body and a white belly, tail and legs.

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• 4. The Stripe Debate

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  Biologists have argued about the purpose of the stripes since at least the 19th century, and six main explanations have emerged.

  Alfred Wallace wrote in 1896 that stripes make zebras less noticeable at night. His camouflage idea, called the crypsis hypothesis, is the earliest explanation. Its supporters thought the stripes suited tall grassland and woodland. Biologist Tim Caro answers that zebras graze in open habitat and are noisy, fast and social. They do not freeze when a predator is near. Woodland ungulates such as bongos and bushbucks have much fainter patterns. A 1987 Fourier analysis found that zebra stripes do not line up with their surroundings. A 2014 study of wild equines found no link between striping and woodland habitats.

  In 2016, Melin and colleagues found that lions and hyenas apparently cannot perceive the stripes from a distance, by day or by night. The pattern would matter only once a predator is close enough to smell or hear its target. They also found that zebras are no less noticeable than solid-coloured grazers on open plains. They suggested stripes might help in woodlands, where dark bands could line up with the outlines of branches.

  Since at least the 1970s, some biologists have argued that stripes confuse predators. The idea comes in several forms. Stripes might make it hard to pick out one animal in a group, to count the group or to trace an outline as the herd runs. They might also hinder a predator tracking a target during a chase, or judging size, speed and direction. A 2014 computer study found that stripes in motion may create a wagon-wheel effect or a barber pole illusion. Caro counters that stripes could make a group look smaller and so more likely to be attacked. Zebras tend to scatter when they flee, and lions catch them by ambush at close range. No correlation turned up between stripe numbers and the populations of mammal predators. In 2021, Hughes and colleagues disputed the idea of motion dazzle. They concluded that moving objects that are solid grey or low in contrast are more likely to escape.

  Wallace first suggested in 1867 that the stripes are a warning, and Edward Bagnall Poulton discussed the idea in more detail in 1890. Zebras fit the profile of known warning-coloured mammals. They are recognisable up close, live in open country, face a high risk of predation and do not hide. Caro objects that lions prey on zebras often, so a warning would fail against them. He adds that zebras lack the defences needed to back up such a signal.

  Wallace also wrote in 1871 that "The stripes therefore may be of use by enabling stragglers to distinguish their fellows at a distance." The social function idea covers recognition, bonding, grooming and signalling fitness. Caro notes that zebra species barely overlap in range. He found no correlation between striping and social behaviour or group size among equines, and no link between striping and fitness.

  In 1971, biologist H. A. Baldwin noted that black stripes absorb heat while white ones reflect it. In 1990, zoologist Desmond Morris suggested that the stripes create cooling convection currents. A 2019 study supported this, finding air swirls where the faster air over warm black stripes meets the air over white ones. Its researchers also concluded that zebras raise their black hairs in the hottest hours to release heat and flatten them as it cools. Larison and colleagues found in 2015 that environmental temperature strongly predicts striping patterns. Others found no sign of lower body temperatures than in neighbouring ungulates, or of striping that tracks temperature. A 2018 experiment dressed water-filled metal barrels in horse, zebra and cattle hides. It found that zebra stripes had no effect on thermoregulation.

  Horse flies spread diseases that can kill equines, including African horse sickness, equine influenza, equine infectious anemia and trypanosomiasis. Zebra hair is about as long as the mouthparts of these flies. Of the six ideas, the fly hypothesis has the strongest support. Biologist R. Harris found in 1930 that flies preferred to land on solid surfaces rather than striped ones. A 1981 study proposed that this explained the stripes. A 2014 study found that striping correlated with overlap with horse fly and tsetse fly populations and activity.

  Caro and colleagues studied captive zebras and horses in 2019. Neither animal deterred flies from a distance, but stripes kept flies from landing, even on horses dressed in zebra-print coats. Effectiveness did not differ between the zebra species, so the different patterns may have evolved for other reasons. White or light stripes painted on dark bodies also reduce fly irritation in cattle and humans.

  How stripes repel flies is less clear. A 2012 study concluded that they disrupt the polarised light that insects use to find water and habitat, but later studies refuted this. Checkered patterns also repel flies, which argues against a barber pole effect. Takács and colleagues suggested in 2022 that in sunlight, temperature gradients between warm dark stripes and cooler white ones stop horseflies from detecting the warm blood vessels beneath. Caro and colleagues concluded in 2023 that high colour contrast and thin bands make it hard for the insects to find a place to land.

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• 5. Grazers and Lions

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  Plains zebras have been recorded travelling 500 km between Namibia and Botswana, the longest land migration of any mammal in Africa. During such journeys they appear to rely on memories of where foraging was best. They may even predict conditions months after they arrive.

  Zebras sleep up to seven hours a day, standing during the day and lying down at night. They use various objects as rubbing posts and roll on the ground.

  Depending on the vegetation available, zebras may spend 60-80% of their time feeding. Grasses and sedges make up most of the diet, though they opportunistically eat bark, leaves, buds, fruits and roots. Their digestive system is simpler and less efficient than that of ruminants, yet they can live on lower-quality vegetation. The plains zebra is a pioneer grazer. It mows down the upper, less nutritious layer of grass and prepares the way for wildebeest, which depend on the shorter, richer grass below.

  Lions are the main predator of zebras. Leopards, cheetahs, spotted hyenas, brown hyenas and wild dogs pose less danger to adults. One study measured a zebra's top speed at 50 km/h and a lion's at 74 km/h. Zebras therefore do not escape by speed alone. They turn sideways, especially when a cat is close behind. Once caught, they are rarely effective at fighting off big cats, though biting and kicking are their defences.

  Against hyenas and wild dogs, zebras may act more aggressively, especially in defence of their young.

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• 6. Family Life

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  Among plains and mountain zebras, a stallion builds his harem by herding young mares away from the groups where they were born. A harem holds one stallion, several mares and their offspring. The groups have overlapping home ranges and tend to be nomadic. They stay stable even when the family stallion is displaced.

  Inside a harem, the females keep a linear dominance hierarchy, and the highest ranks go to those who have lived in the group longest. On the move, the most dominant females and their offspring lead, followed by the next in rank, while the stallion trails behind. Plains zebra groups gather into large herds and may form temporarily stable subgroups, which lets individuals meet animals from outside their own group. Young of both sexes leave the group where they were born as they mature.

  Grévy's zebras live in the arid country of Africa's east, and their adults associate more loosely. Adult males hold large territories marked by dung piles and mate with the females that wander in. The most dominant males claim territory near watering holes, which draws mares with dependent foals and others simply wanting a drink. Less dominant males hold ground away from water, where vegetation is richer, and they attract only mares without foals. A mare with young stays in one territory, which shields her from harassment by outside males and gives her access to resources. In plains and mountain zebras, females mate only with their harem stallion. Grévy's zebras are promiscuous, and the males have larger testes for sperm competition.

  In every species, surplus males gather in bachelor groups. These are mostly young males not yet ready to hold a harem or territory, and they spend most of their time on play fights and greeting or challenge rituals. In plains zebras, the oldest bachelors are the most dominant. Mountain zebra bachelor groups may also include young females that left home early, along with old former harem stallions.

  Fights between males usually concern mates and involve biting and kicking. Among plains zebras, stallions contest recently matured mares, and a mare's father fights off every suitor who tries to carry her away. A healthy harem stallion is rarely challenged. Even when an unhealthy one is replaced, the newcomer slowly and peacefully displaces him. Among Grévy's zebras, quarrels between males flare at territory borders.

  The plains zebra's barking contact call sounds like "a-ha, a-ha, a-ha" or "kwa-ha, kaw-ha, ha, ha." The call of Grévy's zebra has been described as "something like a hippo's grunt combined with a donkey's wheeze." Loud snorting and rough gasping signal alarm. Squealing usually means pain but can also be heard in friendly meetings. Flexible lips allow complex facial expressions. A zebra that drops its ears back and whips its tail is signalling an intention to kick, and stallions threaten with flattened ears, bared teeth and a waving head.

  Plains and mountain zebras strengthen bonds by grooming. Members of a harem nibble and rake along each other's neck, shoulder and back with teeth and lips. Grooming happens mostly between mothers and foals and between stallions and mares, and it sets rank and eases aggression. Grévy's zebras generally do not groom one another.

  Female zebras have oestrous cycles of five to ten days. At peak oestrus a mare spreads her legs, lifts her tail and opens her mouth in a male's presence, and she invites mating by backing in. The male checks her condition with a curled lip and bared teeth, known as the flehmen response. Gestation lasts around a year, and a mare can return to oestrus anywhere from a few days to a month after giving birth. In harem-holding species, a mare's oestrus becomes less noticeable to outside males as she ages, so competition for older females is virtually nonexistent.

  Usually a single foal is born, and it can run within an hour. A newborn will follow anything that moves, so new mothers keep other mares away until the foal learns the mother's striping pattern, smell and voice. Foals begin grazing at a few weeks old but may nurse for eight to thirteen months. Grévy's zebra foals, born into dry country, nurse at longer intervals and begin drinking water only three months after birth.

  When pack-hunting hyenas or dogs threaten a plains or mountain zebra group, the whole group protects the young. The adults form a front with the foals in the centre, and the stallion rushes at predators that come too close. Plains zebra stallions are generally intolerant of foals that are not theirs and may kill them through violence to a pregnant mare. Grévy's zebras do things differently. Their young wait in "kindergartens" while their mothers go to drink, tended by the territorial male. A stallion may even look after a foal in his territory to keep its mother there, though the foal may not be his.

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• 7. Gifts and Emblems

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  Rock art in Southern Africa, dating from 28,000 to 20,000 years ago, depicts zebras, though less often than antelope such as the eland. Folk tales about how the zebra got its stripes sometimes involve the animal being scorched by fire. The Maasai proverb "a man without culture is like a zebra without stripes" has become popular across Africa. The San people connected the stripes with water, rain and lightning, and imagined water spirits bearing the same markings.

  For the Shona people, the zebra is a totem animal, praised in a poem as an "iridescent and glittering creature." Its stripes have symbolised the union of male and female. At the ruined city of Great Zimbabwe, zebra stripes decorate what is believed to be a domba, a school meant to prepare girls for adulthood. In Shona, the name madhuve means "woman/women of the zebra totem" and is given to girls in Zimbabwe. The plains zebra is the national animal of Botswana, and stamps in colonial and post-colonial Africa carried its image. For people of the African diaspora, the zebra came to represent the politics of race and identity, being both black and white.

  Naturalist Thomas Pennant described zebras in 1781 as "the most elegant of quadrupeds." They have become staples of children's stories and wildlife art, including depictions of Noah's Ark, and alphabet books often use them for the letter Z. Outside its range, the zebra was treated as an exotic alternative to the horse. The comic book character Sheena, Queen of the Jungle, rides one, and explorer Osa Johnson was photographed on one. The film Racing Stripes follows a captive zebra shunned by horses, and zebras also appear in Khumba, The Lion King, the Madagascar films and the television series Zou.

  Abstract, modernist and surrealist artists have favoured the animal too. Examples include Christopher Wood's Zebra and Parachute, Lucian Freud's The Painter's Room and Quince on a Blue Table, and works by Mary Fedden and Sidney Nolan. Victor Vasarely drew zebras as black and white lines joined like a jigsaw. Carel Weight's Escape of the Zebra from the Zoo during an Air Raid grew from a real incident, a zebra escaping during the bombing of London Zoo, and tells it in four comic book-like panels. Zebras also lent their name to Zebra Grate Polish, a cleaning product from the British manufacturer Reckitt and Sons, and to the Japanese pen maker Zebra Co., Ltd.

  Zebras have been kept in captivity since at least the Roman Empire, and later they were shipped around the world, often as diplomatic gifts. In 1261, Sultan Baibars of Egypt set up an embassy with Alfonso X of Castile and sent a zebra among other exotic animals. In 1417, Somalia gifted a zebra that was displayed before the Yongle Emperor of China. The fourth Mughal emperor, Jahangir, received a zebra from Ethiopia in 1620, and Ustad Mansur painted it. In the 1670s, Ethiopian Emperor Yohannes I sent two zebras to the Dutch governor of Jakarta, and the Dutch eventually passed them on to the Tokugawa Shogunate of Japan.

  Queen Charlotte received a zebra as a wedding gift in 1762, and crowds in Britain flocked to see it in its paddock at Buckingham Palace. People joked about it as "The Queen's Ass," and George Stubbs painted it in oils in 1763. It also earned a reputation for bad temper and kicked at visitors. In 1882, Ethiopia sent a zebra to French president Jules Grévy, and the species it belonged to was named in his honour.

  Attempts to domesticate zebras have largely failed. They evolved under pressure from many large African predators, including early humans, and that may have made them more aggressive. Still, zebras have been trained. In Rome, they are recorded pulling chariots in amphitheatre games from the reign of Caracalla, which ran from 198 to 217 AD. In the late 19th century, the zoologist Walter Rothschild trained some to draw a carriage in England and drove it to Buckingham Palace to prove it could be done. He did not ride them, knowing they were too small and aggressive. In the early 20th century, German colonial officers in East Africa tried both driving and riding zebras, with limited success.

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• 8. Vanishing Herds

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  The IUCN Red List, as of 2016-2019, lists Grévy's zebra as endangered, the mountain zebra as vulnerable and the plains zebra as near-threatened. Grévy's zebras number fewer than 2,000 mature individuals, but that population is stable. Mountain zebras number near 35,000 and appear to be increasing. Plains zebras are estimated at 150,000-250,000, and their numbers are falling.

  Human activity has fragmented zebra ranges and populations. Zebras are hunted for hide and meat, lose habitat, compete with livestock, and find their travelling routes blocked by fences. Civil wars in some countries have also cut their numbers. By the early 20th century, zebra skins were being made into rugs and chairs. Today trophy hunters may take zebras because a zebra skin rug sells for $1,000 to $2,000. Trophy hunting was rare among African peoples, though the San were known to hunt zebra for meat.

  Early Dutch settlers, and later Afrikaners, hunted the quagga for meat and for skins that were traded or used locally. Its restricted range probably left it vulnerable, and it was easy to find in large groups. The last known wild quagga died in 1878. The last captive quagga, a female at the Natura Artis Magistra zoo in Amsterdam, lived there from the 9th of May 1867 until it died on the 12th of August 1883.

  Protected areas still shelter zebras. Important sites for Grévy's zebra include Yabelo Wildlife Sanctuary and Chelbi Sanctuary in Ethiopia, and Buffalo Springs, Samburu and Shaba National Reserves in Kenya. Plains zebras inhabit the Serengeti in Tanzania, Tsavo and Masai Mara in Kenya, Hwange in Zimbabwe, Etosha in Namibia and Kruger in South Africa. Mountain zebras are protected in Mountain Zebra National Park, Karoo National Park and Goegap Nature Reserve in South Africa, and in Etosha and Namib-Naukluft Park in Namibia.

  The Cape mountain zebra, a subspecies, came close to disappearing through hunting and habitat destruction. By the 1950s fewer than 50 individuals were left. Protections from South African National Parks lifted the population to 2,600 by the 2010s.

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