This is the world biggest migration, which takes place every year on the planes of serengeti in tanzania to masai mara in search of the fresh green grassland. Millions of these wildebeest travels hundreds of kilometres throughout the year only to fight with hunger, following the ecosystem for grazing and water.The journey is beset with danger: young calves are snatched by predators, the slow are brought down by prides of lion, brave beasts break legs on steep river slopes, crocodiles take their share of the stragglers, and the weak and exhausted drown.