Equus burchellii

Geographic Range

The geographic range of Burchell's zebras spreads throughout southeastern Africa, with the highest population densities in the Serengeti-Mara plains of Kenya and Tanzania. Their range reaches as far north as southern Ethiopia and Sudan, as far west as Namibia, and as far south as the northern regions of South Africa. There are also populations in Uganda, Rwanda, Botswana, Zimbabwe, Zambia, Mozambique, and Malawi.

• Biogeographic Regions
• ethiopian ethiopian
  • native native

Habitat

Burchell’s zebras roam the open savannas of southeastern Africa. They prefer open grasslands, open woodlands, and open scrub environments. Occasionally, they may also inhabit taller grasslands, heavier woodland areas, and even hilly country and mountainous regions up to 4,400 meters in elevation. However, they avoid dense forests, deserts, and wetland areas.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

Physical Description

With their distinctive black and white stripes, Burchell’s zebras are easily recognizable. The patterns of their stripes differ from other species of zebras. Their stripes are especially wide becoming wider and more horizontal towards the flanks and rear of the body. The stripes on the neck to the forelimbs are vertical. These neck stripes continue in the mane which is short and sticks straight up. In most populations, the stripes extend to the belly where they meet. Stripes on the limbs are narrower and horizontal and continue until reaching the hooves. Facial stripes are ordered both horizontally and vertically creating beautiful patterns. Not all stripes are distinctly black and white. Some stripes may appear a faint brown or may leave a brown “shadow” stripe in the white region. Within the species, geographical variation in the pattern of stripes exists. In the southern regions, populations tend towards fewer stripes, with a disappearance on the rear, limbs, and belly. They also have longer manes and tend to have stripes that are more buff and brown in color. Each individual's stripe pattern is unique and acts as an identifying characteristic similar to fingerprints in human beings.

Burchell's zebras are 217 to 246 cm in length, with tail lengths of 47 to 56 cm. At the shoulder, their height is 110 to 145 cm. Males are slightly larger than females and usually have thicker necks as well. This sexual dimorphism is not profound, however. Newborn foals tend to have shaggy fur with brownish and buff stripes instead of black and white. One theory for this difference from adults suggests that zebras more easily recognize “dusty” individuals as zebras. Instead of newborn purely white and black foals, they are brownish so they are more easily identified as a zebra. The tails of Burchell’s zebras differ from other equids because they are short and end with a black tuff of hair.

Burchell’s zebras can be distinguished from other species of zebras because the stripes on their flanks meet on their bellies. Both mountain zebras and Grevy's zebras lack stripes on their bellies. Also, the stripes of both mountain zebras and Grevy's zebras are narrower and closer together than those of Burchell's zebras.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

Burchell’s zebras are polygynous; one male stallion leads and mates with a harem of females. Male-male competition is not significant, once males obtain a female, there seems to be a "gentleman's agreement" between the stallions that this female has been taken and cannot be lured away. Because of the lack of competition, males and females look generally the same, with males being only slightly larger than females. Females do not give outward signals of estrous, except for their first estrous. During their first estrous, females signal reproductive status to males through urine. These females take particular stances with their heads up, swan-like, legs straddled and tails up. She is then courted by several males in the area, by both dominant stallions leading a harem already and bachelor males looking for a harem. Eventually, one may try to “abduct” her from her natal group, but the dominant stallion, her father, tries to protect her and prevent her from leaving. Usually, the father is unsuccessful. Females do not ovulate during their first estrous. For the next two years after their first estrous, they will not copulate with males and may drift from group to group until settling on a harem for the remainder of their lives. Unless competing for females in their first estrous, males do not invest much in reproductive behavior. Male zebras fight for access to females in their first estrous. The outcome is vital because the winner of the fight obtains mating opportunities for life. Males bite, kick with their hooves, and circle their competitors. Males also show an excess of affectionate behavior, such as grooming, towards these young females to persuade them to join their harems.

• Mating System
• polygynous polygynous

Burchell’s zebras can breed throughout the year. Most foals are born during the rainy season, which occurs from October to March in East Africa. The peak number of births occurs during the month of January. Each mare gives birth to only one foal after a gestation period of a little over one year. Mares pregnant with twins generally miscarry about 8 months into the pregnancy. When preparing to give birth, mares separate from the rest of the herd to hide from predators. While giving birth, foals and their mothers are extremely vulnerable to predation. Weaning is complete after 7 to 11 months but females may lactate up to 16 months. Young reach independence after 1 to 3 years, when they leave their natal groups. After 16 to 22 months, foals reach sexual maturity but neither males nor females will mate immediately. During this time, females have their first estrous and are “abducted” by outside males competing for them. Males will also leave the natal group at this time, when they roam with a bachelor group of males. If their mothers have another foal, they will leave earlier around the age of 1 years old but most males leave by the age of 2 years old. Young males in bachelor groups play and engage in mock fights, preparing for future fights when they begin searching for available mates and starting their own harems. When they reach 4 years old, males are finally prepared to fight for mates and establish a harem. Females can become pregnant almost immediately after giving birth while they are still lactating during a period called a "foal heat." An estrous occurs 7 to 9 days postpartum and 50% of females become pregnant again during this time. If this occurs, females are investing in two offspring simultaneously. The interbirth interval for Burchell's zebras is generally two years but because of this "foal heat," it can be as little as 13 months.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

Mothers provide the primary care for their young, while the male is busy protecting and defending the harem. Foals weigh about 32 kg when born and are well developed at birth, able to follow the mother back to the herd within a couple of hours. Within 10 or 15 minutes the foal can stand on its own feet and within an hour it is walking around and even running. Foals start to eat grass when they are only one week old. Weaning is complete after 7 to 11 months but females may lactate up to 16 months. During their close association, mothers and foals form especially tight social bonds. For a short period after birth, the mother will keep the foal away from the group, allowing the others to learn to recognize the newborn by smell, sight and sound. For the first year of its existence, the foal stays by the side of its mother learning to keep a watchful eye for predators, learning what grasses to eat, and learning the great migratory routes that cycle in the dry and rainy seasons. However, young males may also associate with their stallion fathers, learning male social behavior within a harem. Stallions offer parental care by defending the group from predators. The harem as a whole acts to defend foals against predators as well. When a member of the group is wounded, Burchell's zebras will surround the predator in a circle, biting and kicking until the predator succumbs or flees.

Harems are organized into a dominance hierarchy. Females of higher rank have been found to produce more offspring and to have shorter interbirth intervals. Stallions show mating preference towards these high ranking females. Immediately after birth, foals take a position in the dominance hierarchy at a position below their mothers.

• Parental Investment
• precocial precocial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • male
    • female
• maternal position in the dominance hierarchy affects status of young

Lifespan/Longevity

In the wild, Burchell’s zebras live an average of 9 years. In captivity they can survive up to 40 years. Population growth and average longevity is most severely impacted by predation. Whereas other grazing herbivores such as gazelles and wildebeests are limited by the abundance of grass, zebras are limited by the abundance of predators. Foals are especially vulnerable with 50% of juveniles annually dieing due to predation. This high rate of juvenile mortality is also partly due to disease, death of mothers, low nutrition, and drought.

Behavior

Burchell's zebras are social, living in permanent family groups composed of one male stallion, 1 to 6 females, and their young. The strong bonds between females are the central relationships within harems. If the dominant stallion leaves or is killed, the harem will remain together waiting for another male to take over. A dominance hierarchy is present in harems and employs a rank order of the dominant male, followed by the mares, and then the foals. The dominant female preserves the rank order by leading the group in single file movements, in which mares line up according to age correlated rank. Foal rank depends on mother’s rank, they stand one place directly behind her in the line and the newest mare of a harem takes the lowest social rank and is placed at the end. The stallion pulls up the rear of the line taking a defensive role in case of predator attack.

Foals leave the family group when they reach 1 to 4 years. Some males leave early as 9 months old, joining bachelor groups. Bachelor groups can have up to 16 members, but are generally composed of only a few males. They are usually formed by young bachelors, but may also have older stallions no longer part of a family unit.

Allogrooming occurs between individuals, especially mares and their foals and stallions and their preferred mares. This is achieved when the grooming zebras stand side-by-side, head to tail and is effective in removing parasites and strengthening social bonds.

Male infanticide and feticide has been noted in captive individuals of Equus burchellii and occur when a new male takes over a harem. In order to gain reproductive advantage the new stallion will kill young foals (infanticide) or force them to abort (feticide) via forced copulation. By gaining reproductive rights to a harem, the stallion is able to ensure that he is only investing parental care in his own offspring. However, infanticide is not always successful and the probability of a stallion killing a foal decreases with the foal’s age.

Several harems come together to form large herds during their migratory journeys. Relationships between harems are relatively cordial and males have a ritual greeting. When they meet, males keep their ears standing up and sniff each others' bodies, especially their necks, nostrils, flanks, and tails. Females from other harems tend to be antagonistic towards each other.

• Key Behaviors
• terricolous
• diurnal diurnal
• motile motile
• migratory migratory
• sedentary sedentary
• social social
• dominance hierarchies dominance hierarchies

Home Range

The home range of Burchell’s zebras is dependent on necessary resources, mostly the availability of fresh water and grazing areas. Herds are non-territorial and occupy overlapping home ranges. Typically, groups occupy ranges of 300 to 400 sq km in the wet season and 400 to 600 sq km in the dry season. They travel up to 13 kilometers daily between resting areas in tall grasslands and grazing areas in short grassland areas. However, the necessity for fresh water and grazing lead to movements of 100 to 150 km seasonally. Burchell’s zebra migration is well-studied in the Serengeti-Mara where, with blue wildebeests and gazelles , herds embark on the largest land migration in the world.

Communication and Perception

Six calls and two facial expressions are used in communication between individuals. Three of the calls are used as predator alert or threat calls, one is used to communicate injury, another is used in distress, and the last one is used in contact between individuals. Additionally, Burchell's zebras are able to visually recognize each other based on stripe patterns, which are as unique to an individual zebra as a fingerprint is to a human. Stallions of different groups greet each other with their ears up. When they sense threat, especially in the form of combat, they will put their ears down. Greetings are also achieved through nose sniffing, rubbing, and genital smelling.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Burchell's zebras are herbivores that primarily graze on grass. They also occasionally browse on herbs, leaves and twigs. Most of their diet (90%) comes from the stems and sheaths of short grasses, especially favored are Themeda triandra , Cynodon dactylon , Eragrustis superba , and Cenchrus ciliaris . Burchell's zebras gather grass by clipping it with their upper lip and lower incisors. They are also well-equipped with large grinding molars which are able to process the tough plant material. Their diet is low in protein, but they process large amounts of food and use hindgut fermentation to help digest tough plant materials.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves
• wood, bark, or stems

Predation

When threatened by predators, Burchell's zebras emit a high-pitched alarm call of the repeating two syllables “kwa-hi”. Mares protect their young foal, while stallions defend their harem with powerful kicks, pushes, and by biting at predators. During the night, at least one member of the harem remains awake hiding in tall grasses to guard and keep an eye open for nearby predators. When chased, individuals reach speeds up to 55 miles per hour. Their striped black and white body patterns are also anti-predatory adaptations, providing camouflage during the nighttime and under dim light. By blending together to look like a gray mass from a distance, the black and white stripes also make it difficult for predators to single out individuals to attack within the herd, a form of disruptive coloration. Also, an individual's stripes make it difficult for predators to discern between the zebra's body and the surrounding vegetation.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Burchell's zebras play an important role in the stability and dynamics of grazing communities where they live. They are an important portion of the east African ungulate faunas that make large-scale, 483 km migratory movements timed to the varying rainy season. They are the first to move in during grass succession, chomping down on old growth and stems which keeps vegetation young and growing. This opens up grazing opportunities for blue wildebeests , gazelles , and topis which are more picky about the vegetation they consume. Zebra herds leave the grazing area during the dry season and in doing so trample the land and stimulate grass growth. This, along with their selection of grass stems, increases the quantity and quality of vegetation for following animal herds. The sheer number of Burchell's zebras gives them a fundamental role in grazing communities. Without zebras, the old vegetation would not be cut back and other grazing animals could not obtain the new growth and higher nutritional leaves they need to survive. Thus, Burchell's zebras are important in maintaining the immense diversity that exists in grazing communities.

Burchell's zebras are hosts to several species of parasitic botflies . Botflies deposit eggs in the zebra’s skin, where the larvae mature until the pupa stage, in which they then leave the host body and continue development in the soil.

Economic Importance for Humans: Positive

Roaming on the Serengeti plains, Burchell's zebras are charismatic animals that attract many people to ecotourism. In certain countries in Africa where other sources of income are unstable, ecotourism can provide a substantial contribution to the overall economy. Because of their distinctive stripes, zebras skins have been historically valuable and serve as an important commodity. Zebra meat provides food for local populations in need. Furthermore, as part of the native ungulate fauna of east Africa, they are critical in influencing vegetation dynamics, on which human cattle and other domestics rely.

• Positive Impacts
• food food
• body parts are source of valuable material
• ecotourism ecotourism

Economic Importance for Humans: Negative

Burchell's zebras are nearly harmless to humans, except for their adverse effect on the livestock industry in Africa. As herbivores, they compete with livestock for water, grass and space. However, they also improve the health of grasslands through their use of tougher plant stems and grass.

Conservation Status

Of all the wild equids , Burchell's zebras are the only species that are not severely threatened or extinct. However, their populations have declined in recent decades, especially in southern Africa. Habitat loss and illegal hunting are the two primary threats that Burchell's zebras face today. Expanding settlements and crop agriculture of growing human populations are destroying their habitats and blocking their cyclical migratory routes. This caused the near extirpation of Burchell's zebras from South Africa, Rwanda, and Angola. In areas where crop growth is difficult, Burchell's zebra populations compete for water and grass with domestic livestock. The presence of zebras near their livestock has led farmers and herders to hunting and fencing. The second primary threat Burchell's zebras face is from illegal hunting. Zebras are hunted for meat and for their skins. Zebra meat is hunted and eaten in local communities, so the hunting trade is locally and not internationally driven. Because zebras spread over large ranges, it is nearly impossible to follow and prevent illegal hunting. Hunting tends to be a larger threat in the northern regions of the zebras’ ranges where political unrest is more common. Seventy-five percent of the Burchell's zebra population is in Tanzania and Kenya. Therefore, the global population is vulnerable to the stability of these countries. Civil unrest and political strife in these countries may have severe impacts on the long term survival of these animals. Political instability corrodes the infrastructure of the park and wildlife reserve organizations needed to maintain ecotourism and conservation. Civil unrest also displaces people from their homes, spreading the range of their livestock into zebra territory and creating a greater demand for meat from the illegal trade.

Other Comments

Four main theories have been purposed to explain the evolution of zebra stripes. The first theory states that these stripes have an anti-predatory function. The stripes may create an “optical illusion” which makes the zebras appear closer than they really are and predators leap too soon when they attack (disruptive coloration). Also, from a distance the black and white colors blend and the massive herd appears gray which enables them to hide better during the night and in dim light. This blending also makes it more difficult for predators to single out individuals from the herd. The second theory proposes that stripes evolved due to social benefits. The pattern of stripes is unique for each individual and serves as a means of identification. Social interactions are based on this particular identification. Studies show that individuals with more stripes receive additional social attention, such as grooming. With these social benefits, it would have been more advantageous to have more stripes. Thirdly, stripes may function in thermoregulation and provide as a natural suncreen. Differences in cooling of the black and white stripes create a rotary breeze. Lastly, these distinctive stripes may protect against tsetse flies . One study demonstrated that tsetse flies prefer solid verses striped objects. None of these theories have been tested thoroughly.

Additional Links

Encyclopedia of Life

Contributors

Liz Colvin (author), University of Michigan-Ann Arbor, Chad Nihranz (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

References

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