The
Grévy's zebra (
Equus grevyi), also known as the
imperial zebra, is the largest
extant wild
equid and the largest and most endangered of the three species of
zebra, the other two being the
plains zebra and the
mountain zebra. Named after
Jules Grévy, it is the sole extant member of the subgenus
Dolichohippus. The Grévy's zebra is found in
Kenya and
Ethiopia. Compared with other zebras, it is tall, has large ears, and its stripes are narrower.
The Grévy's zebra lives in semi-arid grasslands where it feeds on
grasses,
legumes, and
browse; it can survive up to five days without water. It differs from the other zebra species in that it does not live in
harems
and has few long-lasting social bonds. Male territoriality and
mother–foal relationships form the basis of the social system of the
Grévy's zebra. This zebra is considered to be
endangered. Its population has declined from 15,000 to 3,000 since the 1970s. However, as of 2008, the population is stable.
Taxonomy and naming
The Grévy's zebra was first described by French naturalist
Émile Oustalet in 1882. He named it after
Jules Grévy, then
president of France, who, in the 1880s, was given one by the government of
Abyssinia. Traditionally, this species was classified in the subgenus
Dolichohippus with
plains zebra and
mountain zebra in
Hippotigris. Fossils of zebra-like equids have been found throughout Africa and Asia in the
Pliocene and
Pleistocene deposits.
[3] Notable examples include
E. sanmeniensis from China,
E. cautleyi from India,
E. valeriani from central Asia and
E. oldowayensis from East Africa.
[3] The latter, in particular is very similar to the Grévy's zebra and may have been its ancestor.
[3] The modern Grévy's zebra arose in the early Pleistocene.
[3] Zebras appear to be a
monophyletic linage
[4][5][6] and recent (2013) phylogenies have placed Grevy's zebra in a
sister taxon with the plains zebra.
[4] In areas where Grévy's zebras are
sympatric with plains zebras, the two may gather in same herds
[7] and fertile hybrids do occur.
[8]
Description
From left to right: a cranium, a complete skeleton, a left forefoot frontal, and a left forefoot lateral from a Grévy's zebra.
The Grévy's zebra is the largest of all wild equines. It is
2.5–2.75 m (8.2–9.0 ft) from head to tail with a 55–75 cm (22–30 in)
tail, and stands 1.45–1.6 m (4.8–5.2 ft) high at the shoulder. These
zebras weigh 350–450 kg (770–990 lb).
[9][10] Grévy's zebra differs from the other two zebras in its more primitive characteristics.
[11]:147 It is particularly
mule-like in appearance; the head is large, long, and narrow with elongated nostril openings;
[11]:147 the ears are very large, rounded, and conical and the neck is short but thick.
[12] The zebra's muzzle is ash-grey to black in color with the lips having
whiskers. The
mane is tall and erect; juveniles have a mane that extends to the length of the back and shortens as they reach adulthood.
[12]
As with all zebra species, the Grevy's zebra's pelage has a black and
white striping pattern. The stripes are narrow and close-set, being
broader on the neck, and they extend to the hooves.
[12]
The belly and the area around the base of the tail lack stripes which
is unique to the Grevy's zebra. Foals are born with brown and white
striping, with the brown stripes darkening as they grow older.
[12] Embryological evidence has shown that the zebra's background color is dark and the white is an addition.
[3]
The stripes of the zebra may serve to make it look bigger than it
actually is or disrupt its outline. It appears that a stationary zebra
can be inconspicuous at night or in shade.
[12] Experiments have suggested that the stripes polarize light in such a way that it discourages biting
horse-flies in a manner not shown with other coat patterns.
[13]
Other studies suggest that, when moving, the stripes may confuse
observers, such as mammalian predators and biting insects, via two
visual illusions, the
wagon wheel effect, where the perceived motion is inverted, and the
barber pole illusion, where the perceived motion is in a wrong direction.
[14]
Ecology and behavior
The Grévy’s zebra largely inhabits northern
Kenya, with some isolated populations in
Ethiopia.
[11]:147[12] It was
extirpated from
Somalia and
Djibouti and its status in
South Sudan is uncertain.
[2] It lives in
Acacia-
Commiphora bushlands and barren plains.
[7] Ecologically, this species is intermediate between the arid-living
African wild ass and the water-dependent plains zebra.
[11]:147[7] Lactating
females and non-territorial males use areas with green, short grass and
medium, dense bush more often than non-lactating females and
territorial males.
[15]
Grévy's zebras rely on
grasses,
legumes, and
browse for nutrition.
[12] They commonly browse when grasses are not plentiful.
[7][16] Their
hindgut fermentation digestive system allows them to subsist on diets of lower nutritional quality than that necessary for
ruminant herbivores. Grevy's zebras can survive up to five days without water, but will drink daily when it is plentiful.
[17] They often migrate to better watered highlands during the dry season.
[7] Females require significantly more water when they are
lactating.
[18] During droughts, the zebras will dig water holes and defend them.
[7] Grévy's zebras are preyed on by
lions,
hyenas,
wild dogs,
cheetahs and
leopards.
[12] In addition, they are susceptible to various gastro-intestinal parasites, notably of the
Trichostrongylus genus.
[19]
Adult males mostly live in territories during the wet seasons but some may stay in them year round if there's enough water left.
[7] Stallions that are unable to establish territories are free-ranging
[11]:151
and are known as bachelors. Females, young and non-territorial males
wander through large home ranges. The females will wander from territory
to territory preferring the ones with the highest-quality food and
water sources.
[20] Up to nine males may compete for a female outside of a territory.
[12]
Territorial stallions will tolerate other stallions who wander in
their territory, however when an estrous female is present the
territorial stallion keeps other males at bay.
[7][11]:151 Non-territorial males may avoid territorial ones because of harassment.
[15]
When females are not around, a territorial stallion will seek the
company of other stallions. The stallion shows his dominance with an
arched neck and a high-stepping gait and the least dominant stallions
submit by extending their tail, lowering their heads and nuzzling their
superior's chest or groin.
[11]:151 The call of the Grévy's zebra has been described as "something like a
hippo's grunt combined with a
donkey's wheeze".
[7]
To get rid of flies or parasites, they roll in dust, water or mud or,
in the case of flies, twitch their skin. They also rub against trees,
rocks and other objects to get rid of irritations like itchy skin, hair
or parasites.
[12] Although Grévy's zebras do not perform
mutual grooming, they do sometimes rub against a conspecific.
[12]
Reproduction
Grévy's zebras can mate and give birth year-round, but most mating
takes place in the early rainy seasons and births mostly take place in
August or September after the long rains.
[12] An
estrous mare may visit though as many as four territories a day
[20]
and will mate with the stallions in them. Among territorial stallions,
the most dominant ones control territories near water sources, which
mostly attract mares with dependant foals,
[21]
while more subordinate stallions control territories away from water
with greater amounts of vegetation, which mostly attract mares without
dependant foals.
[21]
Zebra mare near younger zebras
The resident stallions of territories will try to subdue the entering
mares with dominance rituals and then continue with courtship and
copulation.
[7] Grévy's zebra stallions have large
testicles and can ejaculate a large amount of
semen to
replace the sperm of other males.
[20] This is a useful adaptation for a species whose females mate
polyandrously. Bachelors or outside territorial stallions sometimes "sneak" copulation of mares in another stallion’s territory.
[20] While female associations with individual males are brief and mating is
promiscuous, females who have just given birth will reside with one male for long periods and mate exclusively with that male.
[20]
Lactating females are harassed by males more often than non-lactating
ones and thus associating with one male and his territory provides an
advantage as he will guard against other males.
[22]
Gestation of the Grévy's zebra normally lasts 390 days,
[12]
with a single foal being born. A newborn zebra will follow anything
that moves, so new mothers prevent other mares from approaching their
foals while imprinting their own striping pattern, scent and
vocalization on them.
[12] Females with young foals may gather into small groups.
[18] Mares may leave their foals in "kindergartens" while searching for water.
[18] The foals will not hide, so they can be vulnerable to predators.
[7] However, kindergartens tend to be protected by an adult, usually a territorial male.
[18]
A female with a foal stays with one dominant territorial male who has
exclusive mating rights to her. While the foal will not likely be his,
the stallion will look after it to ensure that the female stays in his
territory.
[23]
To adapt to a semi-arid environment, Grévy's zebra foals have longer
nursing intervals and wait until they are three months old before they
start drinking water.
[18] Although foals became less dependant on their mothers after half a year, associations with them continue for up to three years.
[7]
Relationship with humans
The Grévy's zebra was known to the Europeans in
antiquity and was used by the
Romans in
circuses.
[3] It was subsequently forgotten in the Western world for a thousand years.
[3] In the seventeenth century, the king of
Shoa (now central Ethiopia) exported two zebras; one to the Sultan of Turkey and another to the Dutch governor of
Jakarta.
[3] A century later, in 1882, the government of Abyssinia sent one to French president
Jules Grévy. It was at that time that the animal was recognized as its own species and named in Grévy’s honor.
[3]
Status and conservation
The Grévy's zebra is considered
endangered.
[2]
Its population was estimated to be 15,000 in the 1970s and by the early
21st century the population was lower than 3,500, a 75% decline.
[24]:11 It is estimated that there are less than 2,500 Grévy's zebras still living in the wild.
[2] There are also an estimated 600 Grévy's zebras in captivity.
[24]:20 Captive herds have been known to thrive, like at
White Oak Conservation in
Yulee, Florida,
United States, where more than 70 foals have been born. There, research
is underway in partnership with the Conservation Centers for Species
Survival on semen collection and freezing and on artificial
insemination.
[25] The Grévy's zebra population trend is considered stable as of 2008.
[2]
The Grévy's zebra is legally protected in Ethiopia. In Kenya, it is
protected by the hunting ban of 1977. In the past, Grévy's zebras were
threatened mainly by hunting for their skins which fetched a high price
on the world market. However, hunting has declined and the main threat
to the zebra is habitat loss and competition with livestock. Cattle
gather around watering holes and the Grévy's zebras are fenced from
those areas.
[24]:17
Community-based conservation efforts have shown to the most effective
in preserving Grévy's zebras and their habitat. Less than 0.5% of the
range of the Grévy's zebra is in protected areas. In Ethiopia, the
protected areas include Alledeghi Wildlife Reserve,
Yabelo Wildlife Sanctuary, Borana Controlled Hunting Area and Chalbi Sanctuary. In Kenya, important protected areas include the
Buffalo Springs,
Samburu and
Shaba National Reserves and the private and community land wildlife conservancies in Isiolo, Samburu and the Laikipia Plateau.
[2]
Near Chilanga, Zambia
Pregnant, Serengeti,
