• LIFE

By Kirsten Weir

CROSSIN

WHAT IMPACT HAS A HUGE FENCE HAD ON ANIMAL

The grasslands of thecountry of Botswanain southern Africaare as wild as theycome. No buildings,no streets, just

open land and untamed creaturesas far as the eye can see. So whatis an enormous fence doing inthis great expanse of nature?For 240 kilometers (150 miles),it stretches across an area calledthe Makgadikgadi basin.

The basin holds a patchworkof national parks and preserveswhere zebras and other animalsare protected species. In 2004, thegovernment of Botswana erectedthe long, electrified fence to keepcattle out and wildlife in.

Zebras are migrating animals.Might the enormous barrier limittheir comings and goings? Scientistswith the Makgadikgadi ZebraMigration Research project havebeen trying to find out. JamesBradley, a biologist at the Universityof Bristol in England, has led theproject since 2009.

HERD BEHAVIORZebras, relatives of horses, are

famous for their distinctive stripes.

As social animals, they live in

groups called herds. Members of a

herd stick together as they graze

the grasslands of their native Africa,

BiologistJames Bradleytracks zebras

in southernAfrica.

always on the lookout for lions and

hyenas that would be happy to

have them for dinner.

Three zebra species exist today.

Bradley studies the plains zebra

{Equus burchelli), the most common

one. The Makgadikgadi is a goodplace to do that. It's home to thesecond-largest population of plainszebras in the world.

"It's a fairly harsh, semiaridenvironment, yet there are some-where between 20,000 and 30,000zebras there," he says. A semiaridclimate receives little precipitation—about 25 to 50 centimeters (10 to20 inches) a year. That's enough,though, to support grasses, shrubs,and other scrubby vegetation.

In the dry season, roughly fromApril to October, plains zebrashang out in the western sectionof the Makgadikgadi. There, anumber of watering holes dot thelandscape along the Boteti River.When rains arrive in November,dry lake beds in the eastern partof the Makgadikgadi fill with waterand the region springs to life. Thezebras follow the rains and migrateeastward to prime grazing spots.

Although tens of thousands ofzebras roam the Makgadikgaditoday, their population is onlyhalf what It was 50 years ago, saysBradley. By tracking the zebras'movements and analyzing theirbehavior, he hopes to understandwhat has prevented their numbers

8 Current Science October 28,2011

A long fence that was built in the African countryof Botswana to separate zebras and other wildlifefrom livestock spans the Boteti River.

MIGRATION IN SOUTHERN AFRICA?

from bouncing back. Might thefence be one factor?

FENCED INConservationists usually think fencesare bad, Bradley says. Fences restrictthe natural movement of wildlifeand can be harmful when, forexample, animals are blocked fromreaching needed food or water. Sofar, though, the Makgadikgadi fencemay not be a bad thing, says Bradley.

Before the fence was erected,zebras often avoided the water-ing holes where cattle and theirhuman handlers stopped to drink,he says, instead, they traveled asfar as 35 kilometers (22 miles) toother sources of water to keep fromrubbing shoulders with the cows.During those journeys, the zebraswent an average of four days, andsometimes as many as seven days,without water.

That was a surprise to Bradley."Zebras are much tougher andmore adaptable animals than wethought," he says. Still, trekkingsuch long distances isn't easy. It's

not unusual for juvenile zebrasto die along the way. Those trekscould be one reason the zebras'population is much smaller than itwas 50 years ago.

Since the fence was built, though,the zebras have been increasing innumber, says Bradley. Their behaviorhas changed too. Before the fence,zebras came down to the river onlyfor quick drinks at night, after peopleand cows had left for the day. Nowthat the cows aren't around, thezebras relax by the river. "They'rechilled out down there," he says.

The fence isn't the only recentchange to the zebras' habitat.Increased rainfall in the past fewyears has fueled a bounty of grasses.Still, Bradley suspects the fence isa factor in the zebra population'supswing. "It might be that if it's usedwisely, fencing can be a positivething," he says.

Bradley is studying not only thefence's impact; he has expandedthe project to learn as much as hecan about the influence of zebrason their environment. Zebras, he

FencesMakgadikgadiPans National

Park

0 10

miles

explains, are a keystone species—ananimal that is critically important tokeeping an ecosystem in balance.

As they graze the tough grassesof the Makgadikgadi, the zebrasclear the way for fresh young grassshoots, which are the food ofchoice for herbivores such as thewildebeest, a type of antelope. Thezebras also are the primary foodsource for predators such as lionsand hyenas. "The number of preda-tors is in decline globally," saysBradley. "To understand why, weneed to understand their prey."

It was in fact a predator, thehyena, that Bradley first studied.Zebras weren't his first love. Butwhen a position at the zebra projectopened up, he came to admire thestriped creatures. "Zebras," he says,"are fantastic animals." CS

v A(fri.in B^ilpy. Aurora HI: Map- Ine leMonnier October 28,2011 Current Science 9

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