During their journey they have to cross the perilous Mara River that lies right across their route.
The migration takes place within the Serengeti- Mara ecosystem.
They spend months trekking Serengeti-Masai Plains until they reach the Mara River.
Wildebeest arrive at the Mara River in their tens of thousands, and gather waiting to cross.
For days they wait for their brothers to arrive and the numbers keep building up.
Eventually the wildebeest choose a crossing point.
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The crossing is the single greatest hurdle the animals face during their journey.
The crossing points form bottlenecks in which thousands of animals perish through trampling or drowning.
The crocodiles capitalize on this to prey on the animals as they struggle to make towards the river bank.
Their journey is long and tough and every year an estimated 250,000 wildebeest never make it.
Sources:Maasaimara,BBC
