Grevy’s Zebra

The **Grévy's zebra** (*Equus grevyi*), also known as the **imperial zebra**, is the largest living wild equid and the largest and most threatened 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*. 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.

## Description

Grevy's zebras have large heads, large and rounded ears, and thick, erect manes. The muzzle is brown. The neck is thicker and more robust than in other zebra species. These qualities make it appear more mule-like than other zebras. The coat has black and white narrow stripes, shaped like chevrons, that wrap around each other in a concentric pattern and are bisected by a black dorsal stripe. The chevron pattern is especially distinct on the limbs, where the point of the chevron points dorsally, becoming more acute the further up the limb they climb; they reach a final peak at the shoulders and the withers. On the cranium, chevrons extend dorsally to the cheek, where the pattern becomes more linear. The belly of this zebra is completely white, unlike other zebras. Grevy's zebras are also the largest of all the wild equids and only domestic horses are larger. Grevy's zebras exhibit slight sexual dimorphism; males are usually about 10 percent larger than females. Grevy's zebra foals are born with a coat that has reddish-brown or russet stripes instead of the black of adults. This gradually darkens to black as the zebra ages. A dorsal mane that extends from the top of the head to the base of the tail is present in all young zebras. This mane is erect when an animal is excited and flat when it is relaxed.

## Range and Habitat

Grevy's zebras live in northern Kenya and a few small areas of southern Ethiopia. Historically, Grevy's zebras inhabited Somalia, Ethiopia, Eritrea, Djibouti, and Kenya in East Africa. The last survey in Kenya in 2000 resulted in an estimated population of 2,571. Current estimates place the number of Grevy's zebras in Kenya between 1,838 and 2,319. In Ethiopia, the current population estimate is 126, over a 90% decrease from the estimated 1,900 in 1980. The eastern distribution is north of the Tana River east of Garissa and the Lorian Swamp. In the west, they are found east and north of a line from Mount Kenya to Donyo Nyiro, and east of Lake Turkana to Ethiopia. In Ethiopia, they are found east of the Omo River north to Lake Zwai, southeast to Lake Stephanie and to Marsabit in Kenya.

Grevy's zebras inhabit semi-arid grasslands, filling a niche distinct from that of other members of the genus Equus that live within the same geographical range, such as wild asses (which prefer arid habitats) and plains zebras (which are more dependent on water than Grevy's zebras). They usually prefer arid grasslands or acacia savannas. The most suitable areas have a permanent water source. In recent years, Grevy's zebras have become increasingly concentrated in the south of their range due to habitat loss in the north. During the dry season, when location near a permanent water source is especially important, zebras tend to become more concentrated in territories with permanent water sources. In rainy seasons, they are more dispersed. Areas with green, short grass and medium-dense bush are used by lactating females and bachelors more frequently than non-lactating females or territorial males. Lactating females may trade off forage quantity and safety to access nutrients in growing grass.

## Reproduction

A male mates with any females that come into his territory if they are in estrous. Mares are usually polyandrous and mate with one male before switching territories and mating with another, although sometimes mares become monandrous. When a mare stays in a single territory, usually because she desires the resources that are present in that territory, she will stay with a single male and mate only with him.

Grevy's zebras can mate year round, but the majority of breeding occurs from July to August and September to October. Foals are born after a 13 month gestation period, usually within the rainy months of the year. Peaks usually occur in May and June, the period of long rains, and in November and December, the period of short rains. As birth approaches, females isolate themselves from the herd. Birth normally takes place lying down, with the young's hoofs appearing first, and full emergence in 7 to 8 minutes. If birth begins with the mother standing, it is completed lying down. The newborn frees itself from the amniotic membranes and crawls towards its mother's head. The mother licks it clean and ingests the membranes and some amniotic fluid, which may be important in initiating lactation or the maternal bond. Zebras take an average of 275 days to be weaned. Once weaned, they continue to stay with their mother. Females disperse sooner than males, females disperse at 13 to 18 months and males often stay with their mother for up to 3 years. A newborn Grevy's zebra foal is russet-colored with a long hair crest down its back and belly. At this stage, imprinting occurs. Female zebras keep other zebras at a distance so that the foal can bond with its mother. Newborn foals can walk just 20 minutes after being born and run after an hour, which is a very important survival adaptation for this cursorial, migrating species. Foals nurse heavily for half a year and may take as long as three years to be completely weaned. Females achieve sexual maturity around 3 years of age and males achieve sexual maturity around 6 years of age. Females tend to conceive once every two years.

## Behavior

Grevy's zebras are different from most other members of the genus Equus in that they do not have concrete social structure. They are loosely social animals; herd composition can vary on a daily basis as new members enter a dominant male's territory and old members leave. The two most stable relationships that Grevy's zebras have are a stallion's attachment to his territory and a mare's attachment to her young. There is not a rigorously observed hierarchy of dominance within a group of Grevy's zebras, although a dominance structure is present. A territorial male has the right to breeding females in that territory. In the absence of females, males will associate in bachelor herds with a loose dominance structure. Males are territorial and claim prime watering and grazing areas. These territories can get up to 6 square kilometers in size. Males mark their territories with piles of dung, called "middens," and emit loud vocalizations that let other zebras know they're present. A territorial male may retain his territory for a period of 7 years before a younger, stronger male challenges him for it. Grevy's zebra males are solitary in their territories, except when females arrive in breeding season. Bachelor males, or non-territorial males, travel together in groups of 2 to 6. This social system is different from other zebras, which form female harems in a single male's territory all year. During droughts, some Grevy's zebras migrate to mountain pastures where food sources are more abundant, but territorial males often remain on their territories year-round.

Lactating females have different resource requirements than non-lactating females. When females are lactating, they need water at least every other day, so male zebras in territories with large, safe bodies of water in them usually get the opportunity to mate with more females. Lactating females have more restricted movements and fewer male associates than non-lactating females. It is possible that male harassment also influences female distribution and associations with males. Lactating females experience higher harassment rates from males than non-lactating females and tend to move faster during harassment periods

## Gallery

Grevy's Zebra Mom with FoalGrevy's Zebra Herd