For the wildebeest, it all begins on the Serengeti Volcanic Grasslands. The combination of fine volcanic soil and the cycles of wet and dry promotes the growth of the wildebeests’ preferred forage. After the Short Rains of November and December, short grasses sprout for a brief time over the ashy volcanic soil. These grasses are at their richest in the southeastern corner of Serengeti National Park where it adjoins the Ngorongoro Crater Conservation area. This is where the calving takes place and where the herd fattens up for the year’s march.
For want of a better place in which to ‘start’ the migration, we’ll begin in January and February, when the wildebeest cows drop their young in a synchronized birthing that sees some 300,000 to 400,000 calves born within two to three weeks of one another, eight and a half months after the rut. The birthing occurs on the short-grass plains that, at the southernmost extent of the wildebeests’ range, spread over the lower northern slopes of the Ngorongoro Crater highlands and are scattered around Olduvai Gorge. Here, at the ‘cradle of mankind’ many notable fossil finds have been discovered, including some that show that wildebeest have grazed the Serengeti almost unchanged for over a million years.
The annual period of birthing provides a feast for predators. Driving across the plains, one can count literally hundreds of hyenas and dozens of lions scattered about. It may seem that the wildebeest are doing the predators a favor by dropping their young all at the same time, but in fact a surfeit of wildebeest veal in very short period results in the predators’ becoming satiated and unable to consume as much as they would if the calving happened over a longer time span. The predators thus have only a limited impact on the population of newborn calves; any calves born outside the peak are far more likely to perish.
To watch any birth is amazing but watching the wildebeest birthing verges on the incredible. A newborn wildebeest gains co-ordination faster than any other ungulates and is usually on its feet two to three minutes after birth. It can run with the herd at the age of five minutes and is able to outrun a lioness soon thereafter. Notwithstanding this, many do die within their first year, from predation (although research indicates only about one percent die this way), malnutrition, fatigue or disease. Many calves get separated from their mothers when the herds panic (which happens frequently) or cross rivers or lakes in their path. The calves then wander for days looking for mum, bleating and bawling incessantly. On rare occasions they may be lucky to find her, but no wildebeest cow will adopt a strange calf, even if she has lost her own and is lactating at the time. As it weakens, a lost calf becomes an easy victim for any watching predator, from jackal up to hyena and lion.
Calving season generally lasts from late January through mid-March, with the largest number of calves born within a two- to three-week span in February. Hundreds of thousands of wildebeest calves are born during this time.
The migratory herds begin to return to the region in January. Calving usually occurs in February, however predicting this event with precision is difficult, one made more difficult by its brevity. In the span of two to three weeks, wildebeest cows will give birth to several hundred thousand calves. While the local predators will take plenty, they cannot take enough to threaten the survival of the herds themselves. The sheer multitude of calves virtually guarantees that tens of thousands will live to adulthood.