The Plains Zebra (Equus quagga, formerly Equus burchelli), also known as the Common Zebra or Burchell's Zebra, is the most common and geographically widespread form of zebra. It once ranged from the south of Ethiopia right through east Africa as far south as Angola and eastern South Africa. The Plains Zebra is much less numerous than it once was, because of human activities such as hunting it for its meat and hide, as well as encroachment on much of its former habitat, but it remains common in game reserves.
Taxonomy
The Plains zebra and the Mountain Zebra belong to the subgenus Hippotigris, but Grévy's Zebra is the sole species of subgenus Dolichohippus. The latter resembles an ass while the former two are more horse-like. Nevertheless, DNA and molecular data show that zebras do indeed have monophyletic origins. All three belong to the genus Equus along with other living equids. In certain regions of Kenya, Plains Zebras and Grévy's Zebras coexist. 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
In 2004, C.P. Groves and C.H. Bell investigated the taxonomy of the zebra genus, Equus, subgenus Hippotigris. They published their research in Mammalian Biology. They revised the subspecies of the Plains Zebra Equus quagga. Six subspecies are now recognizable. The completely maneless Somali population may represent a seventh subspecies: Equus quagga isabella (Ziccardi, 1958). This subspecies may be valid, but at present there is no evidence that it is.
- Quagga, †Equus quagga quagga -- Boddaert, 1785
- Burchell's Zebra, Equus quagga burchellii -- Gray, 1824
- Grant's Zebra, Equus quagga boehmi -- Matschie, 1892
- Selous' Zebra, Equus quagga borensis -- Lönnberg, 1921
- Chapman's Zebra, Equus quagga chapmani -- Layard, 1865
- Crawshay's Zebra, Equus quagga crawshayi -- De Winton, 1896
Physical description
The Plains Zebra is mid-sized and thick bodied with relatively short legs. Adults of both sexes stand about 1.4 meters (4.6 ft) high at the shoulder, are approximately 2.3 meters (8 ft) long, and weigh up to 294 kg (646 lbs) however males may weigh 10% more than females.
Like all zebras, it is boldly striped in black and white and no two individuals look exactly alike. 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; southern populations have varied but lesser amounts of striping on the underparts, the legs and the hindquarters. Southern populations also have brown "shadow" stripes between the black and white coloring. The first subspecies to be described, the now-extinct Quagga, had plain brown hindquarters. (Technically, because the Quagga was described first as E. quagga, the proper zoological name for the most common form of the Plains Zebra is E. quagga burchelli.. Rare albino zebras have been recorded in the forests of Mount Kenya.[2]
Ecology
Range and habitat
Plains zebra are highly dependent on water
Plains zebras live in eastern and southeastern Africa. They can be found in a variety of habitats from treeless grassland to open woodland to wetlands. Zebras rely on rainfall for food and water and thus have to go on great migrations to follow the rains. The zebras will migrate up to 700 miles (1,100 km) for food. Other grazers also must do the same thing. Plains zebras can not survive very long without water and are usually found within 25-30 kilometers of a water source.
Ecological role
Zebras grazing with wildebeest
Unlike many of the large ungulates of Africa, the Plains zebra does not require (but still prefers) short grass to graze on. It eats a wide range of different grasses, preferring young, fresh growth where available, and also browses on leaves and shoots from time to time. In consequence, it ranges more widely than many other species, even into woodland, and it is often the first grazing species to appear in a well-vegetated area. A zebra's digestive system works quickly and can extract more protein from the fibrous and poorest plant parts. Thus zebra are less picky in foraging but they do spend much time eating. Only after animals like zebras have cropped and trampled the long top grasses, which are low in protein, do the other grazers like Blue wildebeests and Thompson's gazelles move in to eat the newly exposed and more nutritional short grasses.
The Plains zebra's major predators are lions and spotted hyenas. Nile crocodiles are also great threats during river crossings. Wild dogs, cheetahs and leopards also prey on zebras, although the threats they pose are generally minor. Hyenas, dogs, cheetahs and leopards mostly attack zebra foals.
Interspecies relationships
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 in one case, a gang of young zebra stallions isolated and harassed a wildebeest calf while keeping the mother at bay. The zebras chased and bit the young calf repeatedly. One zebra even trampled over it. The group eventually lost interest and the calf survived.[3] A similar incident happened when a lone wildebeest calf wandered too close to a gang of stallions and was kicked to death.[4]
Lifestyle
Social structure
The Plains zebra is highly social and usually forms small family groups consisting of a single stallion, one, two, or several mares, and their recent offspring. The adult membership of a harem is highly stable, typically remaining together for months to years. Bachelor males either live alone or with groups of other bachelors until they are ready to start their own harems. Multiple harems and bachelor groups come together to form herds, although these aggregations are highly fluid.
A stallion forms a harem by abducting young mares from their families. When a mare reaches sexual maturity she will exhibit the estrous posture which invites the males. Her father has to chase off stallions attempting to abduct her. Eventually a stallion will be able defeat the father and include the mare into his harem. In addition to the father, the stallion must also fight rival males to get the young mare.
Mares exist in a hierarchy with the alpha female being the first to mate with the stallion and being the one to lead the group. When new mares are added to the group, they are met with hostility by the other mares. Thus the stallion must shield the new mares until the aggression subsides. The most recently added females rank lowest. However females that become unfit or weak may drop in their rank.
Zebras strengthen their social bonds with grooming. Members of a harem nip and scrape along the neck, shoulders and back with their teeth and lips. Mothers and foals groom the most often followed by siblings. Grooming shows social status and eases aggressive behavior.
A stallion will defend his group from other males. When challenged, the stallion would issue 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.
Communication
Zebras communicate with each other with high pitched barks and whinnying. A zebra’s ears signify its mood. When a zebra is in a calm, tense or friendly mood, its ears stand erect. When it is frightened, its ears are pushed forward. When angry, the ears are pulled backward. When surveying an area for predators, zebras will stand in an alert posture; with ears erect, head held high, and staring. When tense they will also snort. When a predator is spotted or sensed, a zebra will bark loudly.
Reproduction
The stallion mates with all his mares. Mares may give birth to one foal every twelve months. Birthing peak during the rainy season. She nurses the foal for up to a year. The stallion is generally intolerant of foals that are not his. It is possible that zebras practice infanticide and feticide, although such incidences have only been observed in captive individuals.[5]
Like horses, zebras are able to stand, walk and suckle shortly after they're born. At the moment of birth a mother zebra keeps any other zebra away from her foal, including the stallion, the other mares and even the previous offspring. Later though they would all bond. Plains zebra foals are protected by their mother as well as the head stallion and the other mares in their group. Even with parental protection up to 50% of zebra foals are taken by predation, disease and starvation each year.
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. The young stallion then seeks out other young stallions for company. Young females may stay in the herd until they are abducted by another stallion.
Anti-predatory behavior
For protection from land predators the Plains Zebra retreats into open areas with good visibility at night time. When the groups forage or sleep one zebra will keep watch and if a predator is spotted it will bark or snort loudly.
When being hunted by hyenas or wild dogs, chases are usually relatively slow, with an average speed of 15—30 km/h. A stallion will attempt to place himself between the predators and the herd, though once a zebra falls behind the protective formation, it is immediately set upon, usually after a chase of 3 km. 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.[6]
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 and an adult zebra is fully capable of driving them away.
Conservation
The Plains zebra’s range has diminished in modern times. While the population remains stable, zebras are threatened by hunting, for their hide and meat, and habitat change from farming. They compete with livestock for food. One subspecies, the quagga, is now extinct. Nevertheless, Plains zebras are protected in most of their range. They are an important economic source in tourism.
References
- Estes, R. (1991). The Behavior Guide to African Mammals, Including Hoofed Mammals, Carnivores, Primates. Los Angeles, The University of California Press.
- Moss, C., Ed. (1982). Portraits in the Wild, Animal Behavior in East Africa. Chicago, The University of Chicago Press.
- Duncan, P. (ed.). (1992). Zebras, Asses, and Horses: an Action Plan for the Conservation of Wild Equids. IUCN/SSC Equid Specialist Group. IUCN, Gland, Switzerland.
- Groves, C.P. & Bell, H.B. 2004. New investigations on the taxonomy of the zebras genus Equus, subgenus Hippotigris. Mammalian Biology. 69: 182-196.
- Hack et al. (2002). Equus burchellii. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 17 June 2006.
- Hack et al. (2002). Equus quagga. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 10 May 2006. (Extinct subspecies of the Plains Zebra.)
- Higuchi et al. 1987. Mitochondrial DNA of the Extinct Quagga: Relatedness and Extent of Postmortem Change. Journal of Molecular Evolution 25:283-287.
- Moelman, P.D. 2002. Equids. Zebras, Assess and Horses. Status Survey and Conservation Action Plan. IUCN/SSC Equid Specialist Group. IUCN, Gland, Switzerland. (http://www.iucn.org/themes/ssc/pubs/sscaps.htm#Equids2002)
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