Zebra
Three species of the genus Equus native to Africa are known as zebra —Equus quagga (common zebra; with five subspecies), Equus zebra (mountain zebra; two subspecies) and Equus grevyi (Grevy's zebra)— whose most distinctive feature is their coloration based on white stripes on a black background.
Etymology
Etymologically, the word zebra used by Spanish speakers derives from the name of the "zevro/a" or "cebro/a", a wild equid that inhabited the Iberian Peninsula at least until well into the Middle Ages. When the Portuguese began to explore the African coast and reached the Cape of Good Hope, in the late of the XV century, they met quagas, a subspecies of the common zebra, which, due to its appearance and wild character, they must have remembered the zebros, for which they gave them the name zevras. savage').
Taxonomy and evolution
The genus Equus arose in North America during the Pliocene. 4.5 million years ago this genus was divided into two lineages, the horse (from which current horses come) and the Stenonian (from which donkeys and zebras come).. The Stenonian lineage crossed into Asia 2.6 million years ago and spread throughout the Old World. Shortly thereafter, two million years ago, African populations diverged from Asian ones, giving rise to the ancestors of today's zebras. The phylogenetic relationship between the different species of zebras is not yet clear. Mitochondrial DNA studies show a closer relationship between the Grevy's zebra and the common zebra, while the mountain zebra would be more genetically related to the African ass. However, nuclear DNA studies are needed to clarify this question.
Species
There are three species of zebras, containing a total of nine subspecies, one of which, the quagga, is extinct.
- Subgender Dolichohippus:
- Grevy snake (Equus grevyi)
- Subgender Hippotigris:
- Common bankruptcyEquus quagga)
- Quagga (E. q. quagga)
- Burchell snake (E. q. burchellii)
- Grant's snake (E. q. boehmi)
- Selous snake (E. q. borensis)
- Chapman's snake (E. q. chapmani)
- Crawshay snake (E. q. crawshayi)
- Mountain snake (Equus zebra)
- Mountain snake of the Cape (E. z. zebra)
- Hartmann mountain snake (E. z. hartmannae)
- Common bankruptcyEquus quagga)
Morphology
Zebras have an average size of 2.3 meters in length, 1.2-1.5 meters in height at the withers and a weight of approximately 300 kilograms, although Grevy's zebras can weigh up to 450 kilograms. In the latter species, males and females are similar in size, but in common zebras and mountain zebras the males are slightly larger.
Zebras have a total of forty teeth: twelve incisors, which are used to cut and tear up pieces of vegetation, four canines, twelve premolars, and twelve molars, all used to grind food before swallowing.[ citation required]
Zebras have excellent eyesight. It is believed that they can see in color. Like many ungulates, zebras have their eyes on the sides of their heads, giving them a wide viewing angle. Zebras also have night vision, although it's not as advanced as most of their predators, but their good hearing makes up for it.
Zebras have a great sense of hearing, and tend to have larger, rounder ears than horses. Like horses and other ungulates, zebras can turn their ears in almost any direction. In addition to good eyesight and hearing, zebras have a keen sense of taste and a very sensitive sense of smell to smoke, essential for surviving fires.
The average life expectancy of zebras is about thirty years, although they can live up to forty years in captivity. In the natural state, where predators represent a constant threat to these animals, the average longevity is approximately twelve years.
Stripes
Zebras are black animals with white stripes. Three observations indicate that they are white stripes on a dark background: first, in the embryo, the development of white stripes and white bellies is later to dark pigmentation (Prothero and Schoch, 2003); secondly, although rare, there are specimens of black zebras with white spots and, thirdly, the rump of the quagga, now extinct, was dark and had no stripes (Rua, 1974).
There are three reasons why zebras are considered to be black with white stripes, and not the other way around, nor that they all have a different frequency:
- White equids could not survive in the plains and forests of Africa.
- The quagga, an extinct subspecies of the common zebra, has the typical stripes in the previous part of the body, but a dark back.
- When the region between the pigmented stripes becomes too wide, secondary stripes appear, as if the suppression was weakening.
The fact that some zebras have pure white bellies and legs is not very conclusive proof that they are white animals, as many different colored animals have white or light colored bellies and legs. Furthermore, the stripes of the zebras are absent in the fetus, which is totally black. The lines appear later, in bands of about 400 micrometers (twenty times the size of a cell). Therefore, the stripes are wider the larger the animal, and they grow in tandem with the size of the body. According to Bard, zebra species differ in the embryonic stage at which the stripes appear. Bard discovered an abnormal zebra, without stripes; its black fur had white dots, which would prove that the stripes are formed by inhibition of melanin production, and therefore the zebra is indeed a black equid with white stripes.
The stripes are usually vertical on the head, neck, shoulders, and trunk, and horizontal on the back and legs of the animal. Zebra crossings take their name from the black and white stripes on zebras.
Zebra stripes are the result of an evolutionary process that amplified a primitive character present in the genus Equus: primitive markings. All the species of this family display these traits to a greater or lesser extent, with some horses and donkeys presenting stripes on their extremities, shoulders, neck and back. In the case of zebras, this trait was enhanced through natural selection, which amplified the size and definition of the stripes and spread them throughout the body.
Why zebras developed such a striking color pattern has long been the subject of speculation. The traditional theories are the following:
- Camouflage mechanism between grass or weed.
- Mechanism of mimeticism among the different members of a herd so that the predator finds it difficult to select an individual from the crowd.
- Recognition function among individuals.
- Thermoregulation mechanism.
It has not been until relatively recently that serious scientific studies on this subject have begun, trying to prove or disprove these and other hypotheses through the collection of statistical data and experiments. To date, these studies have ruled out the first three hypotheses above as determinative, while they have found some correlation between the size and number of stripes and the temperatures experienced by different zebra populations.
However, several studies have concluded that the main function of the stripes is to repel tsetse flies and horseflies. According to experiments carried out in Hungary, these insects find it very difficult to land on surfaces with this type of coloration. Zebras are susceptible to contracting sleeping sickness transmitted by the tsetse fly, a disease that debilitates and in many cases kills the animal that has contracted it. The distribution of this fly almost completely coincides with the distribution of zebras. In fact, the only regions of Africa not affected by this fly are also the only ones that have supported wild equids without the typical zebra striping pattern: African wild asses in Ethiopia, the Horn of Africa and North Africa., and the quaga in southern Africa. On the other hand, horseflies are known to have a special predilection for equines, not in vain in English they are called horse fly (horse fly). Horseflies exist almost everywhere in the world, so zebras are not the only equids that suffer from them. However, in tropical climates, these insects are present in the environment for almost the entire year, while in temperate climates their life expectancy is no more than 3 months. The zebra is the only equine that naturally inhabits these tropical climates, which is why it is by far the most exposed to these parasites.
Diet
Food
Zebras are exclusively herbivorous mammals that eat mostly in the morning and afternoon, replenishing at noon. They are animals that feed on coarse grass, leaves, and shoots. They also eat bark and twigs. Their well-adapted digestive system allows them to subsist on a diet of lower nutritional quality than that required by other herbivores, but it is also less efficient, forcing zebras to spend more than half their time eating.
Zebras can move twenty kilometers in a day in search of food, but at the end of the day they often return to their point of origin. Even so, herds of zebras make a much larger annual migration, which coincides with the dry season and is followed by many other African mammals, representing a movement of hundreds of thousands of animals at a time.
Water
The dry conditions of the ecosystems in which zebras inhabit mean that they have adapted to periods of aridity.
Grevy's zebras are the most adapted to drought conditions. To survive the dry season, when most rivers, ponds, and other sources of water run dry, this species of zebra burrows into riverbeds with its hooves to find water.
The mountain zebra takes advantage of the characteristics of its habitat to survive dry periods. When the water sources on which it subsists dry up, this species simply migrates to a higher altitude, where lower temperatures cause water vapor to condense as rain, snow, or dew.
The common zebra is the least adapted to drought. Unlike the other two species, it always needs to have water available, forcing it to migrate from one place to another depending on the season in search of water resources.
Behavior
Like most equines, zebras are highly social. Even so, their social structure depends on the species. Mountain zebras and common zebras live in groups, known as 'harems,' which consist of a male with up to six mares and their foals. Non-dominant males either live alone or with other non-dominant males until they are large enough to challenge a dominant male. When a group of zebras is attacked by hyenas or wild dogs, the mares huddle with the foals in the middle while the male tries to drive off the attackers.
When a rival male tries to overthrow the dominant male, he challenges him by touching his nose to the rival's nose or rubbing his back against his. This is a type of show of force intended to scare the opponent. If he doesn't give in, they start to fight, biting each other's necks and legs or, in extreme cases, kicking each other; these fights are more dangerous than most fights of this type in the animal world, and a zebra can end up badly injured. The hierarchy of the group is reflected in the order in which its members walk; First of all, the oldest mare walks with her foals, then the other females come in order of age, also with their foals, and the male is the one who closes the group.
Unlike other zebra species, Grevy's zebras do not have permanent social bonds. Groups of this type of zebra rarely stay together for more than a few months. The young remain with their mother, while the adult males live alone. Even so, as in the other two species, the non-dominant males are organized in groups. In cases of food scarcity, many members of this species can congregate around a food source, giving the impression that they form a herd.
During the day, zebras sleep standing up, like horses, and only sleep when they have other animals around to warn them of predators. At night, however, they often lie on the ground. When resting, just like when grooming each other, the zebras lie next to each other, but upside down (ie each zebra has its head to the rear of the other zebra). This has several advantages: on the one hand, it allows the tail of one zebra to scare away flies from the other's face; on the other hand, it offers the animals a 360º viewing angle.
Walking
Like horses, zebras can walk, trot, canter, and gallop. At a gallop, they can reach a top speed of 55 km/h. They are usually slower than horses, but their great stamina helps them evade predators. A zebra being chased will zigzag back and forth to put the predator in trouble. If cornered, the zebra will go into a rampant position and kick and bite its attacker.
Communication
Zebras communicate with each other with neighing and high-pitched moans. Grevy's zebras emit bellows similar to those of mules. Zebras' ears indicate their mood. When a zebra is calm, tense, or friendly, its ears remain erect. When afraid, they move forward. When angry, the ears move back. When zebras search for predators in an area, they remain in an alert posture, ears pricked, head held high, and watching intently. If they are tense, they emit snorts. If a zebra detects or hears the presence of a predator, it will bellow loudly.
Playback
As in most animal species, females reach sexual maturity earlier than males, and may have their first foal at the age of three. Males cannot breed until they are five or six years old. Mares can give birth to a foal every twelve months, which is how long gestation lasts. They care for the young for up to a year. Like horses, zebras are able to stand up, walk, and nurse shortly after birth. At birth, a zebra foal is brown and white instead of black and white. Almost always a single foal is born, but on extremely rare occasions twins may be born.
In the case of mountain zebras and common zebras, the foals are protected by their mother, as well as by the male and the other mares in the group. On the other hand, Grévy's zebra foals only have their mother as their usual protector, since, as stated above, groups of this species tend to disperse after a few months. The protection of foals is especially relevant for these animals, since the young are easy prey for predators and half of them do not survive the first year of life despite the efforts of their mother and the male of the group. Another of the dangers that foals run is that infanticide and feticide have been observed among zebras, despite the fact that this behavior has only been observed in captive specimens.
Dissemination
Originally, zebras ranged throughout Africa. Even so, they became extinct from the north of the continent in ancient times.
Currently, the zebra with the widest range is the common zebra. They live from the savannah-desert transition zones of southern Sudan and Ethiopia, through the eastern African savannah, to the south and southwest of the continent. Grevy's zebra habitats are dry bush and grassy lands of eastern Africa, in Kenya, Ethiopia and Somalia. The mountain zebra has a much smaller distribution than the other two species. It lives in the mountainous highlands of Namibia and South Africa, at altitudes up to 2,000 m.
Dissemination of the common zebra
Dissemination of Grevy zebra
Dissemination of the mountain zebra
Health
Predators and other threats
The main predators of zebras are lions, spotted hyenas, wild dogs and crocodiles. Lions and zebras keep their populations in balance, as lions kill old or sick zebras sooner than healthy and strong ones. And when they are foals they are usually preyed on by leopards, cheetahs and jackals.
The primitive weapons and hunting techniques traditionally used in Africa were not efficient enough to significantly affect zebra populations. Native Africans hunted them not only for their skin, but also for their meat. Even so, the situation changed with the arrival of the European colonizers and their firearms.
Modern humans have had a major impact on zebra populations since the 19th century. Zebras are mainly hunted for their fur. The quagga or quagga, a subspecies of the common zebra, became extinct before the end of the XIX century, while the Cape Mountain was hunted almost to extinction (in the 1930s there were fewer than a hundred specimens left). Since then, the population has grown to approximately 700 individuals, thanks to efforts to conserve the subspecies. Both subspecies of the mountain zebra are currently protected in national parks, but are still endangered.
Grevy's zebra is also endangered. Hunting and competition from livestock have drastically reduced the population. Due to the small population size, environmental hazards, such as droughts, can easily affect the entire species. Common zebras are much more numerous and have a healthy population. Even so, this species is also threatened by hunting and habitat modification caused by agriculture.
Attempts at domestication
Attempts have been made to train zebras as mount animals, as they are more resistant to African diseases than horses. Even so, most of these attempts failed, due to the more unpredictable nature of zebras and their tendency to panic when agitated. For this reason, zebroids (crosses between any species of zebra and a horse, pony, donkey, or donkey) are preferred over pure zebras.
The fourth Mughal emperor Jahangir (r. 1605-1627) commissioned a painting of zebras. In this painting, by Ustad Mansur, the zebra is depicted in stirrups. In England, the animal collector Lord Rothschild often used zebras to move his carriage. In 1907, Rosendo Ribeiro, the first doctor in Nairobi (Kenya), used a saddle zebra for home visits. In the mid-1800s, Governor George Gray imported zebras into New Zealand from his former jurisdiction of South Africa, and used them to move his carriage to his private island, Kawau Island.
Captain Horace Hayes, in Points of the Horse (ca. 1899), compared the usefulness of different species of zebra. Hayes saddled and bridled a mountain zebra in less than an hour, but he didn't get to feed her the two days he kept her. He remarked that the zebra's neck was so stiff and strong that he was not able to twist it in any direction. Despite the fact that he taught her to do what he wanted in a circus ring, when he took her outside he was unable to control her. He found the common zebra easy to tame and considered it ideal for domestication, as it is also immune to the bite of the tsetse fly. He considered the quagga easy to tame because it was stronger, tamer, and more horse-like than the other zebras.
In chapter "9. Zebras and unhappy marriages" In his book Guns, Germs and Steel, J. Diamond also refers to the difficulty of taming zebras:
Any kind of mammal that is large enough is capable of killing a human being. However, some great animals have much more unpleasant provisions and are more incurably dangerous than others.
[... ]
The four species of African zebra are even worse. Attempts of domestication reached the end of hooking them to cars: they were tested as shooting animals in South Africa in the nineteenth century, the eccentric lord Walter Rothschild paraded through the streets of London in a carriage pulled by zebras. Unfortunately, the zebras become terribly dangerous as they age. [...] The zebra has the nasty habit of biting a person and not letting it go. In the U.S., zebras hurt more zoo caregivers every year than tigers themselves. The zebras are also virtually impossible to tie up with a rope—even for cowboys who win round championships capturing with their ties to horses—because of their ability to all test to observe the end of the rope flying towards them, then bend their head and dodge it. Hence it has rarely been possible to saddle or mount a zebra, so the enthusiasm of the South Africans for their domestication disappeared.