When the seasonal summer rains began, the zebras migrated to rain-filled pans in the east to give birth, mate and fatten up on nutrient-rich grasses. With the zebras gone, lions near the Boteti strayed out of the reserve and feasted on cattle. And where lions killed cattle, ranchers killed lions. During the wet season of 2000, cattle farmers destroyed 8 of the park’s 39 lions.
Botswana’s Department of Wildlife and National Parks barricaded the park’s western boundary to keep wildlife and cattle apart: the fence went up along the river, crossing in places between the east and west banks and divvying up the remaining water holes between cattle on one side and zebras on the other. Yet in the dry season, too many animals competed for too little water. Elephants bullied zebras and wildebeest. Prowling lions set off terrifying stampedes of zebras.
In another attempt to protect wildlife during the drought, government authorities and lodge owners in 2007 dug holes and filled them with water from deep below the Boteti sand. “The zebra stood 20 yards away, watching us dig. When we pumped the first water, they were there in an instant,” says Bernie Esterhuyse, operations director of Leroo La Tau safari lodge. “I had tears in my eyes when I saw them finally drink in peace.”
And then in 2009, for the first time in 20 years, high rainfall in Angola, the river’s catchment area, sent a gentle flood down the parched riverbed, and the Boteti began to flow into the reserve again. Crocodiles emerged from dank riverbank caves, where they had holed up for years. The water released hippos from foul puddles full of waste that poisoned fish. And it brought back fish and frogs—and water birds that fed on them.
Thanks to the influx, zebras “no longer need to crowd around pumped water holes,” Bradley says. Now, in addition to studying the impact of the fence and other human interventions on the zebras, Bradley will monitor the animals’ long-term response to the return of the river.
It’s late afternoon when we hear the beep-beep radio signal of a collared mare named Seretse, which means “muddy” in the local Setswana. “She’d been rolling in the pans and was covered in mud when we collared her,” Bradley explains.
Cresting a low hill we’re treated to an extraordinary spectacle. Thousands of zebras upholster the valley below. Wave after wave of them kick up pink dust in the last flush of daylight. They are clustered in small pockets, most moving with their heads low to the ground, tearing through the grass with their teeth. Some stand in pairs resting their heads on each other’s shoulders; others nuzzle and groom their herd mates.
Suddenly three bull elephants stampede across the flanking hillside, trailing clouds of dust. Something has spooked them, and the zebras, too. The zebra herds begin to trot nervously away. Individuals call out “kwa-ha, kwa-ha” to stay in contact with one another. We can’t get close. Bradley decides to call it a day. We make camp in the valley and I fall asleep to the zebras’ haunting calls—until a jackal arrives, howling indignantly at my tent, apparently affronted by its appearance in his territory.
A fresh chorus of kwa-has greets the sunrise. “Yes, yes, we’re coming,” mutters Bradley as he folds his bedroll and we set off to find Seretse. “Zebra really are a keystone species in the Makgadikgadi,” he tells me as we bump along. As the vanguard of the migration, zebras chomp longer grasses, exposing short, sweet shoots for the more selective wildebeest that trail them, while the small population of springbok, bringing up the rear, must settle for leftovers. Then there are the predators zebras sustain. “Lions eat them and brown hyenas scavenge their carcasses,” Bradley says.
His words are barely out when we come upon a tangled heap of vultures. They peel away at our approach, revealing a half-eaten zebra foal. “I was worried I was going to look down and see a collar on it,” Bradley confides as he examines the carcass, taking hair samples and noting his observations: 1-month-old foal, emaciated, no sign of predation. “Natural causes,” he says, meaning anything from illness to starvation. A quick count reveals we’ve interrupted the meal of 44 vultures, four crows and a jackal.