Thin Stripes on a Thin Line
by Howard Youth

Not very long ago, the Grevy's zebra thrived in semi-deserts from present-day Eritrea to western Somalia, and south well into Kenya. There, this striped member of the zebra, ass, and horse family Equidae grazed on tough grasses and traversed acacia- and scrub-peppered plains to drink at isolated water holes and river's edge. Grevy's zebras' constant cropping of grasses may have helped maintain a varied, vigorous plant composition within their range. Meanwhile, they kept their keen ears alert for stalking lions, hyenas, or other predators.

There are two Grevy's zebras at the National Zoo. (Jessie Cohen/NZP)

This was, more or less, a snapshot of the Grevy's zebra in its habitat well into the 20th century. Then along came guns and increasingly large cattle herds. Overgrazing by cattle, excessive hunting, and restricted access to dwindling water supplies have reduced or extirpated the Grevy's zebra (Equus grevyi) from most of its former range, moving it toward the brink of extinction. The zebra's predators also vanished from many areas after being poisoned or shot by herders and ranchers. Today, the ecological footprint of humans and cattle presses far more firmly on the land than that of the zebras. Most Grevy's zebra populations continue to drop, echoing the failing health of the fragile ecosystem upon which they depend.

The World Conservation Union (IUCN) classifies the Grevy's zebra as endangered. In a 2002 "Status and Action Plan for the Grevy's Zebra" created by the IUCN's Species Survival Commission (SSC), biologist Stuart Williams wrote, "In recent history, Grevy's zebra has undergone one of the most substantial reductions of range of any African mammal." The zebra's decline has been swift: In the late 1970s, biologists estimated that 15,000 remained. Today, roughly 2,000 wild individuals remain in Kenya and between 120 and 250 more live in three isolated Ethiopian populations, survivors of an approximately 80 percent drop in numbers.

The Other Zebra
Grevy's zebra was named for Jules Grévy, a former president of France who received one of the animals from Menelik II, king of Shoa and emperor of Abyssinia, in 1882. Today, Grevy's zebras can be seen at the Smithsonian's National Zoo and at many other zoos around the world. They are larger, with more bristly, erect manes, bigger ears, and narrower stripes than the world's two other zebras—the plains or common zebra (Equus burchelli), and the mountain zebra (Equus zebra) of southern Africa.

Grevy's zebra also differs in its habits and habitat, and these two factors are likely connected. The plains zebra thrives in seasonally lush savannas, where males live with and protect harem groups of two to five females and their shared offspring. In their more arid semi-desert habitat, Grevy's zebras, like the African wild ass (Equus africanus), have no permanent social ties outside of the bond between mothers and their offspring. Males hold large territories, through which females drift. Other males are tolerated as well, as long as they do not try to mate with females within another male's territory. Many experts believe that this flexibility allows Grevy's zebras to seek out as many feeding possibilities as they can in their habitat, and quickly breed during brief windows when both ample water and grazing are available.

Females can give birth to single foals once every two years. In times of hardship or inadequate food or water, this interval can slip to once every three years. Youngsters generally stay with their mothers for two to three years before striking out on their own.

Grevy's zebras often associate with other ungulates, which may give them a leg up on predators. For example, they sometimes graze and travel with wildebeest (Connochaetes taurinus), beisa oryx (Oryx gazella beisa), eland (Taurotragus oryx), and plains zebras when their ranges overlap. Although primarily grazers, Grevy's zebras also browse forbs, shrubs, and trees when grasses are scarce.

Large cattle herds may denude the zebra's habitat. Once cows chew plants to the ground, the highly erosive soil and fragile vegetation take far longer to recover than they would in more lush savanna lands where plains zebras generally roam. Prime feeding grounds for Grevy's zebras are now a rare commodity. "The only areas that remain in ‘good' condition are those that are too far from water to be used by livestock or those that were under-used due to continued security threats," writes Williams in the IUCN/SSC's action plan. In most other areas, Grevy's zebras take a backseat to cattle. "As long as pastoral people maintain high grazing pressures in the areas used by them," Williams writes, "it is likely that Grevy's zebra will become increasingly mobile, moving from area to area in search of sufficient food resources."

Another necessity is water. Grevy's zebras pin their survival and reproductive success on it. This vital commodity, however, keeps slipping farther and farther from the animals' reach due to human activities. In their moisture-starved habitat, the zebras must be within fairly easy reach of water holes or rivers. Rains flush these water sources but also transform the land around them. In a case of "just add water," rains turn dusty plains into fertile pastures, increase the animals' access to drinking water—and bring on a peak in Grevy's zebra breeding. In prolonged dry conditions, there is less breeding because females go out of estrus as their bodies adjust more to a state of survival than one of readiness to mate.

Grevy's zebras are adapted to semi-desert and can go without water for two to five days, although they will drink daily if water is available. Lactating females, however, need water every day or two. Females with young stay fairly close to permanent water sources and groups of mothers with foals often travel together.

The zebras prefer to drink at midday, when it is easier to spot lurking dangers. Where cattle keep them from water, Grevy's zebras often drink at night, after herders and their livestock leave. This change in schedule may increase the danger of attack by predators.

Intensive irrigation has dried up many traditional zebra water sources downstream from farm areas. The result has been a dramatic shriveling of the Grevy's zebra's range and population. In addition, herders sometimes block the animals' access to water by fencing water sources with thorn-covered acacia limbs. In many areas where they once abounded, Grevy's zebras, if they appear, seem like distant apparitions—keeping far from people and their cattle.

One reason many Grevy's zebras are skittish is that they are no strangers to gunfire. Through much of the 20th century, hunters shot them for their dazzling pelts, which often found their way into fashionable shops in North America and Europe. In the 1970s, trade in Grevy's zebra skin and parts was curtailed under CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora. In addition, the Kenyan and Ethiopian governments have declared the animal a protected species for more than 20 years. Despite the laws, these large, thin-striped equids still wind up in hunters' sights as food and may be used in traditional medicine.

"The greatest threat to Grevy's zebra in Ethiopia is the prevalence of Kalashnikovs (also known as AK47s) in most areas where they are found," says Alastair Nelson, a biologist who participated in a 2003 survey of Ethiopia's Grevy's zebras. "Beyond this, the [human] population pressure in Ethiopia is reducing habitat available to them, and there is considerable environmental degradation as a result of sustained overgrazing by domestic livestock."

To the south, in Kenyan reserves such as Samburu, Grevy's zebras drink and feed in some of the few refuges free of cattle hordes and guns, but these protected areas can meet their needs for only part of the year. Even in protected areas, the animals are sometimes under stress. Tour vehicle drivers in Kenyan reserves often ignore the rules and stray from the roads, disturbing zebras and other wildlife, causing erosion, and destroying fragile vegetation. And tourists using water holes for swimming may keep day-drinking zebras from vital water sources.

A Brighter Future?
Despite the grim situation, there is much hope for Grevy's zebras if conservationists can stall the steep decline in their population. In recent years, conservation efforts have begun to focus on local communities—the people who share the landscape with these animals.

In January 2003, Fanuel Kebede, a research biologist with the Ethiopian Wildlife Conservation Organization whose work is supported by the U.S.-based Wildlife Trust, convened a workshop on the conservation of Grevy's zebra and the critically endangered African wild ass. The workshop was conducted in the Afar region of Ethiopia, where populations of both species live. It brought together biologists, regional and federal government leaders, local elders, and game scouts. "Having the communities support research and conservation is critical," says Patricia Moehlman, an equid biologist who works with Kebede. "The Ethiopian elders were supportive of the conservation of Grevy's zebra and the African wild ass but it will take a long-term commitment by everyone," says Moehlman.

The picture is most bright at the southern end of the zebra's range in central Kenya. There, a robust, well-studied population of about 1,000 Grevy's zebras moves through three game reserves—Buffalo Springs, Samburu, and Shaba. But even this large population is declining. While there are usually Grevy's zebras in these parks, they frequently come and go, spending much of their time on unprotected lands. According to the IUCN/SSC action plan, less than 0.5 percent of Grevy's zebras' range falls within protected areas. While outside the parks, the zebras compete with cattle herds for limited water. Likely as a result, this population, like most others, is highly mobile, has a low juvenile survival rate, and is in steady decline. "Foal survival has been directly related to the extent to which their mothers move," reads the action plan. "There is low foal survival when mares make large or frequent small-scale movements," as many must do when their water sources become more difficult to visit or locate.

Not all private lands, however, prove to be poor feeding and breeding areas. Grevy's zebras thrive on the nearby Lewa Plateau, an area once considered marginal habitat for them. There, the Lewa Wildlife Conservancy, a private conservation organization run from a cattle ranch-turned-wildlife sanctuary, works with local communities and Saint Louis Zoo and Princeton University biologists to save Grevy's zebras and other wildlife.

On the Lewa Plateau, local ranchers now have a growing appreciation for the Grevy's zebra's place in the ecosystem, as well as its appeal to tourists. On a number of large holdings, ranchers removed fences to increase the animals' access to grazing and water. Some also periodically burn savannas to improve the quantity and quality of grassland. In addition, the habitat managed by conservancy members may now be better for Grevy's zebras because elephant, giraffe, and other large browsing animal populations are healthy. These browsers clip back the bush cover, encouraging increased grass growth and thus greener pastures for zebras.

Today, this area is one of only a few that support a healthy Grevy's zebra population. About 420 live there, and Lewa is now considered an important birthing area and a source area for the populations that have been sinking nearby.

The plains zebra traditionally reigned supreme on the Lewa and biologists are studying to what extent the two zebras now compete against one another. "We found that habitat preferences of the two species were similar but not identical. Largely, they share most of the habitat and spend most of their time together," says Dan Rubenstein, professor and chair of the Department of Ecology and Evolutionary Biology and director of the Program in African Studies at Princeton University. Rubenstein and his colleagues have dedicated much of their time in recent years to learning more about Grevy's zebra biology, while working to build bridges between communities and conservation programs.

Differences in behavior sometimes set the two species apart. Grevy's zebras without young in tow move farther from water than plains zebras ever do. "This provides [Grevy's zebras] with a spatial refuge, which reduces competition to some degree, but the real impact of competition is best measured by changes in feeding rate," says Rubenstein. While 420 Grevy's zebras inhabit Lewa lands, they share the acreage with about 1,200 plains zebras.

After studying the feeding rate of both species on a local level, Rubenstein and his colleagues believe that the presence of many plains zebras harms Grevy's zebras. "The bottom line is that plains zebras disproportionately consume vegetation when they locally outnumber Grevy's zebras. We think Grevy's zebras then lose condition, which compromises their health and makes it harder for them to rear offspring." Lewa now holds about 20 percent of the world population of Grevy's zebras and Rubenstein and others are considering ways that managing plains zebra numbers might help keep the area's Grevy's population afloat.

But there is another problem. "Grevy's zebras represent a disproportionate share of the diet of lions on Lewa," says Rubenstein. He and his colleagues Kenyan biologists David Njonjo and Belinda Low studied hairs collected from dried lion dung and found two results: Zebras constitute about 70 percent of the diet of Lewa lions, and Grevy's zebras make up about 55 percent of the zebras killed.

If plains zebras far outnumber Grevy's zebras, why does the less common species more often wind up a meal for a hungry lion? Rubenstein hypothesizes that it's basic behavior that makes the difference. While plains zebra females always travel with males that kick at attacking lions, Grevy's zebra males patrol large territories, leaving females to fend for themselves. In arid areas to the north where Grevy's zebras once flourished, lion densities were traditionally low, so the temporary absence of males was not such a problem.

Rubenstein and his colleagues collaborate with local data-gatherers thanks to a Saint Louis Zoo-funded scout program that employs nine people in the Samburu pastoral communities of Nagroni, Naibelibeli, and Serolipi. "Scouts go out and do what they normally do: Women collect wood and water, men herd livestock," says Rubenstein. But scouts also carry with them field checklists and GPS units. When they spot Grevy's zebras, they note details such as location, weather, features of the habitat and landscape, behavior, and interactions between livestock and wildlife. "These are data we can't gather while driving around in a Land Rover, especially in the woodlands," Rubenstein says. "What has emerged from their data is unbelievably interesting. For example, we have learned that herds get larger during the day, a pattern that is unique to landscapes they share with livestock."

"This year," says Rubenstein, "we took the data back to the community." Biologists met with local elders and prepared cartoons to illustrate the results of statistical analyses of zebra behavior and conservation needs. Chiefs translated Swahili and English into the local Samburu language. "When we asked the local people why they thought Grevy's herds were larger from 3 p.m. to 7 p.m., there were chuckles," says Rubenstein. "Some people said, ‘Maybe they're waiting for us to go home.' The villagers realized that their cows are all over the best grasslands until nightfall and that this might have an impact on the zebras. This kind of presentation leads to fruitful discussions."

Much fieldwork remains to be done before scientists can clearly understand Grevy's zebra ecology and distribution. This proves very difficult in areas racked by political or tribal violence, and where gun-shy zebras do their best to keep out of sight. So far, most of the behavioral studies focused on Grevy's zebras have taken place in the semi-arid lands of Kenya. Scientists still do not know if the zebras exhibit regional differences in behavior or if other aspects of the populations vary. Also, no one currently knows if the scattered populations have genetic differences, although Rubenstein and his colleagues, with the support of the National Science Foundation, are extracting DNA from the dung of Grevy's zebras to determine if certain fragmented populations show genetic subdivision. In Ethiopia, Kebede has collected Grevy's zebra fecal samples in the northernmost, isolated Alledeghi population, which will add a new dimension to these analyses.

Just knowing how many zebras remain has been a challenge. Since 1978, surveys have been done in different ways and in different seasons. "It's not entirely clear how much the animals living along the Ethiopia-Kenya border move," says Moehlman. For example, the population found in Chew Bahir in southwestern Ethiopia may cross into Kenya. "The question in my mind is are they moving down into Kenya and hence not counted? Just about every time a survey's been done, it's been done a different way. Surveys need to be done regularly and with the same methodology. We also need to count Grevy's zebra in southern Ethiopia and northern Kenya at the same time."

There have been intriguing reports of Grevy's zebras in a fourth location in Ethiopia as well as in southern Sudan, where a pilot named Charley Trout saw some while he was flying in relief supplies in the 1990s. These animals may represent new and unknown populations, so biologists like Moehlman are keen to find ways to assess their numbers and conservation status.

Zoos play vital roles in educating people about the plight of Grevy's zebras. They provide opportunities for people to observe these animals firsthand and to learn about their situation in the wild. Some zoo programs support research that engages local communities and answers some of the many questions remaining about this rare zebra's natural history. The Grevy's zebra population in North American zoos is managed by a Species Survival Program (SSP) under the auspices of the American Zoo and Aquarium Association. The National Zoo's role in the SSP is to serve as a holding facility, where young males live until the SSP recommends that they go to another zoo for breeding. SSP management helps ensure that the zoo population does not lose genetic diversity. The maintenance of genetic diversity in zoo Grevy's zebras is an important safeguard for wild populations, although the reintroduction of zoo-bred animals is not currently being considered as a conservation action.

For now, conservationists hold out hope for remaining wild populations. "As long as there are refuges where Grevy's zebras are highly valued," says Rubenstein, "there will always be some. But if we really want to boost populations we have to find ways for the economic development of local people to go hand in hand with Grevy's zebra conservation. The local pastoral people's wealth is in their herds. If Grevy's zebras also have value to them, then maybe we can turn the corner."

Moehlman agrees. "The future viability of Grevy's zebra populations is absolutely dependent on local [human] populations. You have a complicated set of factors, including a semi-arid habitat where people are struggling to survive. Community-based conservation, good research, and the commitment to the local communities involved benefits not only the Grevy's zebra but the whole ecosystem."

—Contributing editor Howard Youth first saw Grevy's zebras feeding with beisa oryx ten years ago, during a FONZ tour that visited Kenya's Samburu Game Reserve.

ZooGoer 33(6) 2004. Copyright 2004 Friends of the National Zoo.
All rights reserved.