The wildebeest migration in East Africa is a continuous and cyclical movement of wildebeest herds between different areas in search of food, water, and suitable breeding grounds. It is not a one-time event but rather a year-round process. The entire migration cycle lasts throughout the year and involves different phases. Here's a rough breakdown of the timeline:

Calving Season (Late January to February): The migration typically begins in the southern Serengeti in Tanzania, where wildebeest herds gather to give birth to their calves. The timing of this phase coincides with the start of the short rains and the availability of fresh grass for the young calves.

Dry Season (June to September): As the dry season progresses and the grasses in the southern areas are depleted, the wildebeest herds begin their northward migration. They follow the rains and the growth of new grass.

River Crossings (July to October): One of the most dramatic phases of the migration is the river crossings, particularly at the Mara River in Kenya. As the herds move north, they encounter rivers that must be crossed to reach better grazing areas.

Return South (November): As the dry season comes to an end and the grasses in the northern areas are also depleted, the wildebeest herds start their journey back to the southern Serengeti, often arriving in November. This return migration ensures that they have access to fresh grass for the calving season the following year.

Calving Season Again (Late January to February): The migration cycle begins anew with the calving season in the southern Serengeti.

So, as you can see, the wildebeest migration is a continuous process that spans the entire year. The duration of their migration is a year-round cycle with no fixed endpoint. It is driven by the changing seasons, the availability of resources, and the need for survival and reproduction. The wildebeest are constantly on the move, making it one of the most remarkable wildlife spectacles in the world.