The Great Migration, month by month

The Great Migration is the year-round movement of wildebeest, with zebra and gazelle, around the Serengeti–Mara ecosystem. It has no start or finish. The herds loop clockwise from the short-grass plains of the southern Serengeti and the Ngorongoro Conservation Area, north-west through the park, north into Kenya's Maasai Mara, and back south again: a circuit of roughly 800 kilometres.

Most of that loop is in Tanzania. Kenya holds the northern end, which the herds usually reach in the dry season, from around late July or August.

The table below is the usual pattern. The herds follow the rain, and the rain does not keep a calendar, so a wet or dry year can move everything by several weeks. Operators and camps track the herds day to day; treat any month-by-month guide, this one included, as a starting point, not a promise.

The simple answer is grass. The herds are grazers on a scale the land can't carry for long in one place, and they follow the rains to wherever the grass is fresh.

The fuller answer is in the soil. The treeless short-grass plains of the south-eastern Serengeti lie on volcanic ash blown from the neighbouring volcanic highlands, and research published in Ecology in 2025 identifies these as the most phosphorus-rich soils in the park. Phosphorus and calcium are exactly what a lactating wildebeest needs, which is why the herds return to the southern plains to give birth there during the wet season.

When the rains stop, those plains dry out quickly. The herds move towards the permanent water and taller grass of the west and north, and come back when the rain returns.

In February the herds are on the southern plains and give birth in a remarkably short window. Around half a million calves are born within two to three weeks. Biologists see the timing as a defence: when so many calves arrive at once, predators can take only a fraction of them before the rest are strong enough to keep up with the herd.

It is also when the predators are most active. Lion, cheetah and hyena concentrate on the plains, and this is one of the best times of year to see a hunt.

The centre of it is the Ndutu area. Lake Ndutu itself lies just inside the Ngorongoro Conservation Area, on the Serengeti boundary, so conservation-area rules and fees apply there rather than national-park ones.

The crossings people picture are on the Mara River in the northern Serengeti, from about July. Herds bunch on the bank, sometimes for hours or days, then pour down the cut banks into water where crocodiles wait. They cross back and forth through the dry season, so there is no single crossing to catch.

On their way north the herds also cross the Grumeti River in the western corridor, a smaller river than the Mara.

A crossing cannot be scheduled. Seeing one well mostly means being in the north for several days and being patient on the day.

The figure you will see everywhere is about 1.3 million wildebeest. It comes from aerial surveys, the method used since the 1970s; the most recent survey by the Tanzania Wildlife Research Institute (TAWIRI), in 2023, again estimated roughly 1.3 million.

In 2025 a team of researchers from Princeton, Oxford, Twente and other institutions published a different count in PNAS Nexus. Using AI to detect animals in high-resolution satellite images from August 2022 and 2023, they counted fewer than 600,000, about half the accepted figure.

The authors say the two methods should be seen as complementary rather than contradictory. Their images covered part of the range at one time of year, some wildebeest may have been outside the area surveyed, and satellite images can't yet tell a wildebeest from a zebra or eland beside it. If the lower number is right, it could mean the herds have declined, or that past counts were too high. Nobody knows yet, and the researchers are calling for aerial and satellite surveys to be flown together to settle it.

Whichever figure is right, it remains one of the great wildlife spectacles on earth.