When Do Wildebeest Give Birth? Calving Season on the Plains

The calving season, step by step

For the migrating blue wildebeest of Tanzania and Kenya, the calendar looks like this:

• May to June: the rut. As the long rains end, the herds move northwest and males compete for females. Most conceptions happen in a burst of about three weeks.
• About 8 to 8.5 months of pregnancy as the herds travel north to the Maasai Mara and back.
• Late January to March: calving. The herds are back on the short-grass plains of the southern Serengeti and the Ndutu area of the Ngorongoro Conservation Area. Births peak in February.

At the height of the season, many thousands of calves are born each day; a figure of about 8,000 a day is often quoted. Roughly 80–90% of all calves arrive within a two- to three-week window.

Outside East Africa the timing differs. In southern Africa, most wildebeest calves are born around November and December, at the start of the rainy season. Everywhere, the aim is the same: to give birth when grass is fresh and rich.

Why the southern plains?

The short-grass plains of the southern Serengeti grow on soils formed from volcanic ash. The grass there is short but especially rich in minerals such as phosphorus and calcium, and in protein. That is exactly what a nursing mother needs to make milk and what a growing calf needs to build bones.

The plains are also open and treeless. Predators have fewer places to hide, and herds can spot danger from far away. When the rains end in about April or May and the plains dry out, mothers and calves set off together on the Great Migration.

Why give birth all at once?

Giving birth in such a narrow window is a defense called predator swamping. Spotted hyenas, lions, cheetahs, leopards and African wild dogs all hunt newborn calves. If births were spread through the year, predators could pick off calves steadily. When hundreds of thousands are born at once, predators can eat only a small fraction before the calves grow strong and fast.

Wildlife biologist Richard Estes, who studied calving on the Serengeti plains in the 1970s, found that calves born during the peak survived better than the few born early or late. Late calves are especially easy to spot among older, bigger calves and are often singled out by hyenas.

Herd size matters too. Calves born into large herds survive much better than those in small groups; one widely cited figure is about 80% survival through the first month in large herds compared with about 50% in small ones.

The first minutes of life

Wildebeest mothers usually give birth in the middle of the herd and often around the middle of the day, when many predators are resting. That gives the calf the rest of the daylight to become steady on its feet.

A newborn weighs around 19 kg (42 lb). It usually stands within a few minutes and can follow its mother soon after, and within a day or two it can run with the herd. This makes wildebeest calves “followers”, unlike the young of many antelopes, which lie hidden in long grass for their first days. As explained in Is a wildebeest an antelope?, this suits a life spent on open plains with nowhere to hide.

Mother and calf learn each other’s smell and voice in the first hours. In the crowded, moving herd this bond is vital: a calf that becomes separated from its mother is rarely adopted by another female and often does not survive.

Growing up

Calves are born a tawny brown and begin turning gray at about two months. They start nibbling grass within weeks but continue to nurse for many months, sometimes until shortly before the next calf is due.

At about eight months to a year, young males leave their mothers and join groups of other young males. Young females usually stay with the herd. Females can breed from about 16 months old if they are well fed, but most give birth for the first time at about three years and then have one calf a year.

How many calves survive?

Even with predator swamping, the first year is dangerous. Calves are lost to predators, to separation from their mothers, to disease and drought, and later to the river crossings of the migration. In many years, a large share of calves do not reach their first birthday.

Still, enough survive to keep the Serengeti population at roughly 1.2–1.5 million wildebeest. The calving season is one of the great wildlife events in Africa, and it is the moment when the herds’ remarkable timing is easiest to see.