Over time the disease reached a sort of equilibrium. Every decade or so it would rise up and kill off cattle, wildebeest and buffalo. “The populations eventually stabilized,” Sinclair said, “so that there were 15,000 buffalo and 100,000 to 200,000 wildebeest, and over the years everyone came to think that this was the way the Serengeti had always been.”
The disease brought other changes. Without prey to hunt, the number of lions, hyenas and other predators also dropped. And the number of trees increased.
A forest isn’t the first thing that comes to mind when one thinks of the Serengeti. Yet when the colonial administration set up the first game reserve here in 1929, dense woodlands of thorny acacia trees had sprung up across the plains. The trees were even thicker when the park was officially established two decades later. But then they began to disappear.
“The older trees were all dying,” said Sinclair, “and there weren’t any seedlings. Something was killing the forest. And park officials were very worried. They were losing their ‘natural, pristine’ forest. They wanted to know why, and they wanted to know what to do. It was all very confusing. The wildebeest and buffalo were booming, and the trees were dying.”
As it happens, an effective vaccination against rinderpest had been developed in the early 1960s, and veterinarians inoculated the cattle around the Serengeti. The wild ungulates began to rebound. But the trees continued to dwindle. One day in 1980 Sinclair came to the very spot where we were now sitting to photograph what he thought was one of the last trees in the Serengeti. “Here’s the picture I took of this hillside,” he said, pulling a yellowed photograph from a folder and pointing to the slope immediately across from us. In the photograph, a single acacia spreads its limbs over a barren, rocky slope.
When he returned to the spot five years later, Sinclair found that the tree was surrounded by hundreds of tiny, spindly seedlings. “There was an explosion of trees here, and in fact all over this part of the Serengeti. And ever since, the trees have been increasing and increasing. Just look at this hillside.” Indeed, it was virtually hidden under a cover of dense young trees. “That’s how quickly things can change here,” Sinclair said.
Two things led to the forest’s rebound. First, the wildebeest population grew to its current size, between 1.2 million and 1.5 million animals. And all those wildebeest ate more grass each year, in the process turning the long-grass plains into short-grass plains. As a result, human-set fires that sweep through the Serengeti each dry season don’t burn as hot as they did when the grass stayed long and so do not consume as many acacia seedlings. “The elephants were also ‘culled,’” Sinclair said, bracketing the word with his fingers. “Illegal hunters poached thousands of elephants here in the late 1970s and throughout the 1980s, leaving very few of them to eat the young trees. So, yes, the lions are increasing,” Sinclair said. “But that’s because of these dense forests that have grown up because the wildebeest keep the grasses short.” More forest means more cover for the lions; they catch more prey, have more babies and form more prides. Their numbers go up.
But what if something happened to the wildebeest? “That is the one change it cannot withstand: the total loss of the wildebeest,” Sinclair said. “They keep the entire ecosystem going. We would not have a Serengeti without them. It would be something else.”
The Serengeti of the early 21st century is different from the Serengeti of 1950 and 1850. Aside from being smaller, its rhinos, elephants, roan antelope and wild dogs are far fewer. The Maasai people, who lived in the national park until the 1950s, have been replaced by tourists, researchers and park employees in cars. One can argue about whether these changes made the park less natural. But in a time of great extinctions, here in the Serengeti we humans have done something rare: we have set aside a corner of the earth for the animals.
Early one evening I joined Sinclair’s four Tanzanian research assistants on a nighttime survey. Ernest Eblate sat behind the wheel of the Land Rover, and I took a seat next to him while the other three crowded into the back. Eblate handed me a clipboard, saying, “You’re our secretary tonight.” The men in the back would be spotting and calling out the animals, and I would record their numbers, species and other details.