The Great Migration

From the air it resembles a river of dark bodies flowing across a sea of gold, a column of animals so long that its head and its tail lie beyond the reach of a single glance. On the ground it is a wall of sound and dust, the grunting of more than a million wildebeest moving as one great organism across the plains of East Africa. This is the great migration, the annual circuit of the Serengeti and Maasai Mara ecosystem, and it is among the most spectacular wildlife events on the planet.

Following the Rain

The migration has no beginning and no end. It is a loop, a roughly circular journey of hundreds of kilometres that the herds complete each year, driven by the search for grass and water. The rhythm of it is set by the rains. When the short rains green the southern plains, the wildebeest gather there to calve, timing the birth of their young to the season of fresh, nutritious grass. When those plains dry out, the herds move north and west in search of grazing that the rains have renewed elsewhere, and so the circle turns.

The calving is one of the migration's great marvels. Over a few short weeks, hundreds of thousands of calves are born, a flood of new life so concentrated that the predators of the plains cannot possibly take them all. This is no accident. By synchronising their births, the wildebeest overwhelm the hunters through sheer numbers, ensuring that most calves survive the dangerous first days. A newborn wildebeest can stand within minutes and run with the herd within hours, an urgency bred into it by a life lived under constant threat. No other large mammal is so quick to find its feet, and on the open plains, where there is nowhere to hide a helpless infant, that speed is the difference between life and death.

The wildebeest do not travel alone. Zebra move with them in great numbers, and the two species complement one another: the zebra crop the tall, coarse tops of the grass, leaving the shorter, more tender growth that the wildebeest prefer. Thomson's gazelles and other grazers follow in their turn, each taking its share of the renewed pasture. The migration is not a single species on the move but a whole community, shifting across the landscape in a procession that the plains have known for ages.

The River Crossings

The most dramatic moments of the migration come at the rivers. As the herds press north, they reach the broad, muddy channels that cut across their path, and there they must cross. The water is deep, the banks are steep and slick, and the current is strong. Worse, the rivers hold crocodiles, some of them enormous, that have waited all year for exactly this feast.

The crossings are chaos. The wildebeest mass on the bank, hesitating, milling, until some pressure within the herd finally breaks and they plunge in, thousands of animals pouring into the water at once. Many make it across. Some are taken by the crocodiles, dragged under in a thrash of jaws and spray. Others drown in the crush or break their legs on the far bank and are left behind. It is a brutal toll, paid year after year, and yet the herds pay it because the grass on the other side is worth the risk.

What the migration demonstrates, above all, is interdependence. The grass feeds the wildebeest; the wildebeest feed the predators and the crocodiles; their dung and their trampling and their dying bodies feed the soil and the scavengers and the plains themselves. Remove the migration and the whole system would unravel. It is a reminder that the great wonders of the natural world are rarely the achievement of a single species, but the product of many lives woven together across a landscape, moving, as the wildebeest move, to a rhythm older than memory.