Mammals
Blue Wildebeest
Connochaetes taurinus · also called blue wildebeest, common wildebeest, brindled gnu
The blue wildebeest looks like an animal assembled from spare parts — the head of an ox, the mane of a horse, the beard of a goat, the sloping back of a hyena. It is also the engine of the greatest wildlife spectacle on the planet: a herd of well over a million that never stops walking.
Overview
Blue wildebeest live in the grasslands and open woodland of eastern and southern Africa. They are pure grazers that need short, growing grass and water every day or two, and it is this constant need for fresh pasture that keeps them moving. Both sexes carry smooth, curved horns, and the herd is intensely social — wildebeest are almost never alone.
The great migration
The Serengeti–Mara herd — about 1.3–1.5 million wildebeest, plus hundreds of thousands of zebra and gazelle — follows the rains in a roughly circular, year-round journey across the Tanzania–Kenya ecosystem. Each animal covers around 800 kilometres a year. There is no beginning or end; the herd is always somewhere on the loop.
Calving
On the southern plains in the wet season, 80–90% of females calve within two to three weeks. Predators kill huge numbers of calves but cannot keep up with the sudden glut, so most survive. A wildebeest calf can stand and run within minutes and match the herd’s pace within a day.
The river crossings
Where the migration meets the Mara and Grumeti rivers, the herds bunch on the bank and then cross in a stampede. Trampling, broken legs, drowning, and crocodiles kill thousands at every major crossing — a grim but essential nutrient pulse into the river system.
Status
The blue wildebeest is Least Concern as a species (~1.5 million), but its future is bound up with freedom to move. Fences, farms, and settlement have collapsed non-migratory herds by up to 90%, and the great migration itself is regarded as one of the most fragile large natural systems remaining.
Blue Wildebeest: common questions
What is the wildebeest migration?
It is the year-round, roughly circular movement of about 1.3 to 1.5 million blue wildebeest — together with a few hundred thousand plains zebra and Thomson's gazelle — around the Serengeti ecosystem of Tanzania and the Maasai Mara of Kenya, following the rains and the fresh grass they bring. There is no start or finish; the herds are always on the move. Broadly, they calve on the southern short-grass plains around February, head northwest through the western corridor in the dry season, cross into the Mara around July to September, and return south when the rains resume. Each animal walks around 800 kilometres a year.
Why do so many wildebeest give birth at the same time?
Roughly 80 to 90 percent of blue wildebeest calves are born within a two-to-three-week period in the wet season, on the mineral-rich short-grass plains. This "predator swamping" means that although lions, hyenas, cheetahs, and jackals kill enormous numbers of calves, they simply cannot eat more than a fraction of them in such a short window, so most calves survive the critical first days. Calves are also astonishingly precocious — they can stand and run within about five minutes of birth and keep pace with the moving herd within a day, which is faster than almost any other hoofed mammal.
Why do the river crossings kill so many wildebeest?
At the Mara and Grumeti rivers, tens of thousands of wildebeest pile up on the bank, and the crossing happens as a sudden stampede triggered by the pressure of animals behind. In the chaos, wildebeest are trampled, break legs on the steep banks, are swept away by the current, or exhaust themselves and drown. Large Nile crocodiles gather at the traditional crossing points and take many. Thousands die at the crossings each year, and their carcasses are a massive food subsidy for crocodiles, vultures, and the river ecosystem itself.
Is the wildebeest endangered?
As a species, no — the blue wildebeest is Least Concern, with around 1.5 million animals, most of them in the migratory Serengeti–Mara herd. But the picture depends entirely on being able to move. Non-migratory and blocked populations have collapsed — the wildebeest of Botswana's Kalahari fell by around 90% after veterinary fences cut them off from water, and other herds have declined as land is fenced, farmed, and settled. The migration is considered one of the most fragile large-scale natural phenomena left on Earth.