The Maasai Mara National Reserve is a wilderness area of about 1510 km² that forms the northern tip of the 27,000-km² Serengeti/Mara ecosystem. Wild animals roam freely and can be seen in vast numbers. Every year it hosts 'the migration', which takes place between July and October. Over a million wildebeest and two hundred thousand zebra pass through on their endless journey, following the rains in search of grass. Predators are well represented with cheetah, leopard, hyena and the largest lion population in Kenya. There are many different varieties of antelope and gazelle along with elephant, hippo and crocodiles.