Threats

The wildebeest migration has followed its present circuit of the Serengeti Plain for hundreds of thousands of years. The wildebeest were joined on the plain by Maasai herdsmen 2500 years ago. The Maasai did little to disrupt the ancient patterns, but the activities of both the wildlife and pastoral herdsmen reshaped the landscape to better suit both. The traveling herds fertilized the soil and crushed nascent shrubs and trees and encouraged the grass to grow. The Maasai set fires to burn away stubble and shrubs, prompting new growth, and they rotated their cattle from pasture to pasture to prevent overgrazing. The Serengeti-Mara ecosystem we know today is the result of the complex interplay of geography, climate, wildlife, and people.

Disruption of one or more of elements of the ecosystem unbalances the larger system, often in unexpected ways. When European settlers arrived in East Africa in the 1890s, they brought with them cattle infected with rinderpest. In only a couple of decades, the virus reduced the continent's populations of wildebeest and buffalo and giraffe by 90%. The migratory Serengeti herds of a million and a half wildebeest were reduced to a few hundred thousand. Rinderpest decimated Maasai cattle herds, too, of course, while European settlers claimed the most fertile land for themselves. In response to fewer wildebeest and fewer Maasai cattle, the grasslands began to change. Fire and a million stamping wildebeest had once controlled the advance of shrubs and trees; now nothing did. Denser bush led to a proliferation of tsetse flies - deadly to both livestock and people. Some early conservationists celebrated the emergence of the tsetse as "nature's game warden." The creation of game parks and reserves, and widespread rinderpest inoculation of cattle, allowed the Serengeti wildebeest herd to regenerate. By the 1970s the herd again numbered more than a million wildebeest. Post-colonial land-use practices have allowed the Maasai to return to many of their historic pastures, too.

The migration today is much like it has always been, but the balance is precarious.

The migration is threatened by encroaching human populations just as many of the world's wild places are. The complex of reserves and conservation areas that encompass most of the ecosystem - Serengeti National Park, Maasai Mara Reserve, Ngorongoro Conservation Area and associated wildlife corridors and buffer zones - is large, 10,000 square miles, about as large as the state of Massachusetts. In times of drought the protected area may not be large enough for the herds as they push into the settlements on the fringes. In all times the protected area is too large for the growing number of people who live on its boundaries. Fences erected by farmers and ranchers restrict the animals' movements outside the parks. Bushmeat hunters, often subsistence farmers living near the parks, illegally poach as many as 160,000 migratory herbivores each year. Arrests for illegal hunting in the Western Corridor rise and fall with the arrival of the migration. What is true for lions is true for bushmeat hunters; predators tied to the land must wait for prey that is tied to the migration.