One of Earth’s great wildlife migrations: a 2023 survey estimated about 1.37 million wildebeest moving through the connected Serengeti-Mara ecosystem, chasing rain and fresh forage on a loop of about 800 km.
The Serengeti-Mara ecosystem spans Tanzania and Kenya. A 2023 wet-season survey estimated 1,366,109 wildebeest, with substantial uncertainty.
Each year the herds walk a loop of around 800–1,000 km, depending how much of the Mara and side routes you count, always chasing rain-green grass. About 80% of Serengeti wildebeest young are born within a roughly three-week period on the southern plains.
At studied Mara River drownings, birds consumed an estimated 6–9% of soft tissue. Grass quality sorts grazers into different feeding niches.
When rinderpest was eradicated, wildebeest increased, grazing reduced fire, and woodland carbon recovered through a measured cascade. Only a few thousand cheetahs remain across Africa — the Serengeti is one of the last open stages they can still use.
Wildebeest are also called 'gnus'.
Lions are primarily nocturnal and often hunt in the cooler hours after dark.
Unlike lions, the cheetah cannot roar at all — instead it purrs and chirps like a bird.
Rainfall and fresh forage drive the migration through the connected Serengeti-Mara ecosystem.
Field Notes
The Great Circle
Rainfall and fresh forage drive an annual wildebeest migration through the connected Serengeti-Mara ecosystem. Each year the herds walk a loop of around 800–1,000 km, depending how much of the Mara and side routes you count, always chasing rain-green grass.
A 2023 wet-season survey estimated 1,366,109 wildebeest, with substantial uncertainty. The herds follow grass that grows after the rains across Tanzania and Kenya.
Grass quality sorts grazers into different feeding niches along that shared stage.
Research Report
The Baby Boom
On the southern plains, wildebeest calving is tightly timed. About 80% of Serengeti wildebeest young are born within a roughly three-week period in the main calving season.
That pulse of calves is part of the same rain-and-forage calendar that moves the herds. When rinderpest was eradicated, wildebeest increased, grazing reduced fire, and woodland carbon recovered through a measured cascade — one reason this baby boom still reshapes the plains.
Expert Dossier
Nature's Clean-Up Crew
At studied Mara River drownings, birds consumed an estimated 6–9% of soft tissue. Grazers, scavengers and nutrient cycling connect the migration to the grassland after those river crossings.
A 2017 estimate put the global cheetah population at about 7,100 adult and adolescent animals; later assessments may differ. Only a few thousand cheetahs remain across Africa — the Serengeti is one of the last open stages they can still use.