WHY DO ANIMALS MIGRATE?

There is combinations of factors that cause animals to migrate. The main reason however, is to ensure enough food and water throughout the year. In the Serengeti Ecosystem animals basically alternate between the Short Grass Plains in summer and the wooded, tall grass areas in winter. The short grass plains have a low rainfall and lack surface water, except for the temporary pans during the wet season. The tall grass woodland in the north and west has a higher rainfall with perennial rivers.

Wildebeest,

Form the bulk of the migration, being the numerous. They prefer short grasses but they do eat tall grasses, especially after these have been “trimmed” by Zebra and Buffalo. They thrive on the new shoots of grasses.

Zebras,

Form the second largest group of migratory animals and largely follow the same route as the wildebeest. They congregate on the plains during the rainy season when food is abundant. AS soon as becomes scarce, they break up and disperse in the family units. Their dispersal minimizes grazing pressure in the low production tall grasses areas.

Eland,

They have the ability to browse [eat leaves] as well as graze [eat grass] and are very well adapted to almost any environment from lowlands mountains. Although they do not follow the same migratory route as Wildebeest, they also alternate between the plains and woodland.

Thomson’s Gazelles,

They have a much shorter route than the Wildebeests. They feed only on short grasses, herbs and forbs. They are the first to arrive on the plains and the last to leave.

Grant’s Gazelles,

They do not really need to migrate as they are water independent, but they do move to a limited extent, mainly locally. Their route is in some cases opposite to that of migratory species, spending the rainy season in open patches within the woodland and the dry season on the plains.

The short rains begin around early November. A little after this, in late November and December, the herds of the wildebeest migration arrive on the short-grass plains of the Serengeti. These are south and east of Seronera, around Ndutu and include the north of the Ngorongoro Conservation Area. Dispersed across these plains, wildebeest and zebra are everywhere – feeding on the fresh, nutritious grasses. They stay here through January, February and March, with most wildebeest calves born in a short window around February. Gradually they spread west across these plains, then around April they start their great migration north.
By May the Serengeti's wildebeest all seem to be moving north, migrating to seek fresh grazing and water. The area around Moru Kopjes and west of Seronera is then hectic with a series of moving columns, often containing hundreds of thousands of animals – joined by many zebra, and a scattering of Thomson's and Grant's gazelles.
Some of the migration then head due north of Seronera, but most are usually further west. Around June the wildebeest migration is often halted on the south side of the Grumeti River, which has some channels which block or slow their migration north. The wildebeest then congregate there, in the Western Corridor, often building up to a high density before crossing the river. The river here is normally a series of pools and channels, but it's not continuous – and so whilst they always represent an annual feast for the Grumeti River's large crocodiles, these aren't usually quite as spectacular as the crossings of the Mara River, further north.

The wildebeest migration continues moving northwards during July and August, often spreading out across a broad front: some heading through Grumeti Reserve and Ikorongo, others north through the heart of the Serengeti National Park.
September sees the herds spread out across the northern Serengeti, where the Mara River provides the migration with its most serious obstacle. This river gushes through the northern Serengeti from Kenya's adjacent Maasai Mara Game Reserve. Watching the frantic herds of the wildebeest migration crossing the Mara River can be very spectacular; there are often scenes of great panic and confusion. It's common to see herds cross the Mara River north on one day, and then back south a few days later.
By October the wildebeest herds are migrating again with more accord: all are heading south, through western Loliondo and the Serengeti National Park's Lobo area, returning to the green shoots which follow the rains on the short-grass plains of the southern Serengeti in November.