A World Heritage Site and Biosphere Reserve, Serengeti National Park is undoubtedly one of the best known wildlife sanctuaries in the world, famed for its annual wildebeest migration. Aptly referred to as endless plains by the Maasai, Serengeti provides sanctuary to the highest concentration of plains animals in the world. Within its area of 14,763 sq km are more than 4 million large mammals living in total wilderness freedom. About 35 species of plains animals can be observed including elephants, buffaloes, topi, wildebeest, gazelles, zebras, lions, leopards, cheetahs and over 400 species of birds can be observed in the Serengeti National Park. The main game drive areas in the Serengeti are the Seronera Valley, the Western Corridor, Lobo or northern Serengeti, and the south eastern Serengeti plains extending to Ndutu in the Ngorongoro Conservation Area. The Seronera valley in central Serengeti, endowed with permanent surface water, attract a large concentration of wildlife throughout the year. From December to April, south eastern Serengeti plains provide the best opportunities for game viewing as hundreds of thousands of the migratory animals including wildebeest and zebras are concentrated in this part attracted by the short palatable grass. Between May and July, when drought sets in, Serengeti is the site of one of the most breathtaking events in the animal kingdom – the migration of thousands of wildebeest heading southwest, north or west in search of water and greener pastures in and around the National Park. According to the Serengeti National Park official guide Lines and columns of wildebeest up to 40 km long have been observed (from the air) heading southwest, north or west as the wildebeest trek to the woodland zone. The Lobo area in northern Serengeti remains rich in wildlife during the dry months of August to November when most of the game has moved from the grass plains in the south. This is also true of the Western Corridor towards Lake Victoria when the migration usually lingers in the area between June and July.A large part of the migratory animals move into Maasai Mara in Kenya by September, staying there hardly three months before streaming back into northern Tanzania and the Serengeti plains in November. The Serengeti Migration has been named one of the Seven Natural Wonders of Africa.