Every year, at the end of June, over 1.5 million wildebeest arrive to Masai Mara (Kenya) from Serengeti (Tanzania). The Great Migration is the largest overland migration in the world. The animals, that go back to Serengeti at the end of October, travel a total of 800 km in each cycle and often cross the Mara river in search of good pastures. During the migration around 250,000 wildebeest and 30,000 zebra are killed off as a result of predation by carnivores, but also from thirst, hunger and exhaustion. The most dramatic and dangerous moments for them are the "crossings". Herds of thousands of wildebeest cross the river at the same time in the middle of crocodiles and hippos.