Thomson's gazelles populate the Serengeti.

There are more Thomson's gazelles on the Serengeti Plain than almost any other creature -- a good thing, given how many other animals seem to want to eat them. Thomson's gazelles number more than 500,000 in the Serengeti, an area not much larger than Vermont. As seen in the NATURE program BORN TO RUN, "tommies," as they are affectionately called, follow the wildebeest through their annual migration across the Serengeti National Park in East Africa.

The wildebeest helpfully crop the park's coarse grasses, exposing the herbs and shoots that are tommies' preferred food. When the southern grasslands dry out, both species move north and west to the bush country in search of food, then later travel back to the replenished grasslands. And everywhere the tommies go, it seems, someone is waiting there to make a meal of them: cheetahs, lions, honey badgers, jackals, hyenas, leopards, crocodiles, and other species large and small.

The tommie is easily identified by its distinctive black stripe and ever-wagging tail. It is a surprisingly small gazelle, weighing only about 60 pounds when fully grown. It is well known for its "stotting" maneuver, in which it jumps high into the air, straight up, looking almost as if it is bouncing on a trampoline. In BORN TO RUN, a tommie stots to warn the rest of the herd that a hyena is on the prowl -- and to let the hyena know that he'd better look elsewhere for an easy catch. 

The Thomson's gazelle was named by one of the first foreigners to venture into the Serengeti region of Kenya and Tanzania. British explorer Joseph Thomson, leading expeditions for the British Royal Geographical Society, walked across much of the area in the late 1870s. It was not long after that, says ecologist A.R.E. Sinclair of the University of British Columbia, that the Serengeti started to go through some drastic changes. Sinclair, who has studied the Serengeti ecosystem for the last 30 years, is currently conducting a large-scale biodiversity survey of the area. "When conservationists starting paying attention to East Africa in the 1930s, '40s, and '50s," says Sinclair, "they saw it covered with beautiful umbrella trees and they assumed that that was how Africa should be naturally. But we now believe that before white men arrived, it was much more a grassland with a few scattered trees." Rather than seeing the current ecosystem as a forest whose decline has been caused by elephants, Sinclair believes the Serengeti is now just rebounding to its natural state.

The trouble began in 1890, he says, when colonists brought with them the rinderpest virus, which wiped out the cattle population and much of the grazing wildebeest. Their stock devastated, cattle ranchers left the area, and with few grazing animals to cut back young shoots, trees took over the plains. Around the 1930s, the British government began clearing land, people moved back in, and man-made fires opened up more of the land. "The wildebeest is rebounding after the removal of the virus," says Sinclair. "The area is returning to the state it was in before white man arrived."

The ecosystem is relatively healthy now, but it is not entirely safe from human intervention. "The Serengeti now is being pinched by expanding human populations on all sides," says Sinclair. "The most significant feature of the Serengeti is the wildebeest migration. They move in an annual cycle through the system, but the park is too small to contain them." The animals are clashing with farmers on the outskirts of the park, and Sinclair has become aware that large commercial farmers may want to put up fences to keep the animals out. "On the Kenya side where they tried to do that they got their guns out and mowed them down. Shades of what happened to the bison here [in North America] in the last century. We're worried that that could happen on a larger scale in a more critical area. It hasn't happened yet, but I suspect that greed and money will eventually override conservation."

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