Zookeeper Journal


Zebra
Equus grevyi, Equus burchell, Equus zebra

Status in the Wild: Endangered (Grevy's Zebra)

It’s dusk in the African savannah and the zebras are thirsty. Hours of grazing the tough, dry grass under the hot sun has left the herd exceptionally parched. Their passage to the river’s edge, however, is stopped short upon sight of a pair of reptilian eyes breaking the water’s surface. Keenly aware of the crocodile’s presence, the zebras face an overwhelming dilemma: die by thirst or die by crocodile. Ever skittish, the zebras at the front of the herd make aborted attempts to drink. They are so near the water they can almost taste it, yet the ominous crocodile remains a dangerous obstacle. Nonetheless, the herd moves forward cautiously, inching their snouts towards an uncertain future.


Zebras are the end product of 60 million years of evolution, and it all began with a small forest browser that looked more like a greyhound. According to the fossil record, the descendants of this small animal eventually became bigger, their legs longer, and their teeth better adapted to temperate grasslands. 

Finally, two million years ago, the modern horse appeared. It is believed that it originated in North America and, because it was so superbly adapted, spread across all the continents evolving into six different species. Four of the six ended up in Africa, and they include three zebra species and the African wild ass, source of all domestic donkeys and asses. Zebras, horses, and wild asses all belong to the Equid family.  

Equids belong to a group called ungulates - hoofed mammals that include antelope, swine, rhinos, hippos, and even elephants. Like horses, zebras are single-hoofed ungulates, built for speed and endurance. They can run 60 miles per hour for a few hundred yards, or maintain 30 to 40 miles per hour for up to 15 miles. Also, zebras have strong upper and lower incisors to grind and crop the toughest grass, though male zebras have spade-shaped canines that they use in fighting. Unlike horses, zebras have manes that are made of short, erect hair, and their tails are tufted at the tip. 

Zebras are most renown for their stripes. The ancient Greeks believed that zebras were a cross between a tiger and a horse and called it a “hippotigris,” or “horse tiger.”  Of course, such a pairing between two separate species is biologically impossible. When early Romans tamed zebras for their circuses they called them, “the horses of the sun that resemble tigers.”  

The stripes function as camouflage, creating an optical illusion called disruptive colouration that breaks up the outline of the zebra’s body. This illusion makes it difficult for predators, such as lions, to distinguish individuals from the rest of the herd.  

Some researchers suggest that the stripes also serve as a form of air conditioning, controlling the zebra’s body temperature. In the sun, the zebras’ glossy coat dissipates over 70 percent of incoming heat. But the dark stripes reach higher temperatures, causing air to rise. This generates a cooling airflow over the lighter areas, helping maintain the zebra’s body temperature during hot weather. 

Stripes also distinguish one zebra species from another. The stripes on Grevy’s zebras are narrow and more numerous than on other zebras, and do not extend to the belly.  

The Burchell, or plains zebras, are the most completely and boldly striped. Lastly, the stripes on the mountain zebra are closer at the torso and absent on the belly. Interestingly, each individual zebra has its own unique stripe pattern, like fingerprints on a human. Most researchers can identify individuals using chest patterns, but sometimes rump patterns may be used also. 

Grevy’s are the largest of the zebra species - taller and heavier with a massive head and large ears. They are named for Jules Grevy, president of France in the 1880’s who received a zebra from Abyssinia as a gift.  

Once numerous in Africa, Grevy’s today only number several thousand, and they are confined mostly to parts of northern Kenya. Though they require less water than other zebras, Grevy’s must still compete with domestic livestock for water. They have also suffered enormous losses from poachers who value their meat and skins. 

Burchell’s zebras inhabit much of Africa’s savannahs from Sudan to South Africa, and they are one of Africa’s most adaptable and successful grazers, utilising a broad range of grassland, from treeless grasslands to open woodlands. Finally, the mountain zebra lives in the arid mountain ranges of southern and south-western Africa.  

Burchell’s are among the most water-dependent of the plains game animals. Mountain zebras, however, dig for subsurface water, excavating pits that are defended against other animals and herd members alike. In the dry season, Burchells and Grevys can live on tough, dry grass as long as they are within 20 miles from water.         

Zebras are often on the move because they live in environments where resources are widely scattered. Males are highly territorial and will defend their resources violently against other males. Related females and individuals of similar social and reproductive status tend to remain closely tied. The strongest bonds occur in family groups where members actually look out for one another. 

If one family member becomes separated from the rest, the others will search. Also, families will adjust their travelling pace to accommodate the old and the weak. Should lions or hyenas attack a family group, the members form a semi-circle facing the onslaught. If a family member is injured, the rest will often encircle it to protect it from further attacks. 

The females, or mares, within a family observe a strict hierarchical system. The highest-ranking mare always leads while the others follow her in single file, each with their foals directly behind them.  

 

The lowest- ranking mare always brings up the rear. The stallion is the dominant member of the family, but he operates outside the system and has no special place in the line. Mares will react aggressively to outsiders, including foals. Offspring leave the herd in their adolescence, but mares often get abducted to other harems.  

On the other hand, males voluntarily join bachelor herds until they mature at 5-6 years old.Their nomadic way of life probably led to the development of the equid harem, a herd of mares controlled by a single stallion. Even if herd stallions are replaced, unrelated mares will continue to associate, spending their entire adult lives together. 


The ties that bind zebras are reinforced through mutual grooming, which appears to play a role in reconciling differences and confirming social status. It commonly involves individuals of unequal rank where the lower-ranking individual always takes the initiative; the higher-ranking zebra may refuse by turning away or making threatening gestures, or it may respond in kind. 

Often a pair of zebras on friendly terms will stand together and simultaneously nibble the hair on each other's neck, shoulders, and back. Standing in this position, either head-to-tail or looking over each other’s shoulder, makes it possible for the two zebras to swish flies off each other’s faces; and with heads up they can see predators in all directions.  


Some studies say that social grooming occurs less frequently among mares, but it appears to happen more often between mothers and foals, and between siblings. This suggests that maternal and kinship bonding is the primary reason for social grooming.  

 

Zebras may congregate in herds as small as seven individuals or as large as 150,000. They sometimes associate with other animals, such as gnus and giraffes, though their attitude towards these animals can be characterised as “benign indifference.” Antelopes and zebras, however, actually seem to enjoy each other’s company.

The herd spends a majority of their time eating. Zebras eat mostly vegetation high in fibre but low in protein. In order to consume an adequate amount of nutrients, they have to spend as much as 60 to 80 percent of their time eating, night and day, depending on food availability.  

During famine, zebras will resort to eating bark and roots.  In the midday heat, zebras will spend as much as 7 hours a day sleeping, often while standing. At night, they will sleep with their legs gathered or flat on their sides. During times of rest, there is almost always one member of the herd that stands alert for possible signs of predators.  

Archaeological evidence shows that horses were probably tamed and ridden about 5,000 years ago in southwestern Asia. Though people over the centuries have tried to tame zebras as pack animals, most attempts to domesticate them have failed due to their unpredictable behaviour. Simply, zebras do not like being ridden! 

Grevy’s are the most endangered of the zebra species. Hopefully they will not go the way of the quagga, said to be the most horse-like of the striped-equids. It was one of the southernmost subspecies of the plains zebra with a bright bay body and dark striping confined only to the head, neck, and forequarters. 

 

The name “quagga” comes form the Hottentot tribal name “quahha,” a word that imitated the animal’s explosive, bark-like bray. Settlers regarded the animal as competitors for grass and water needed for livestock. Unfortunately, the quaggas were exterminated in Africa, and the last one died in the Amsterdam Zoo in 1883.



Sources and Suggested Readings

Estes, Richard Despard, The Behaviour Guide to African Mammals, Berkeley: University of California Press, 1991

MacClintock, Dorcas, Animals Observed, A Look at Animals in Art, New York: Charles Scribner’s Sons, 1993