The Ngorongoro Conservation Area (NCA), measuring 8,300 square kilometres, is the only place on earth where mankind and wild animals co-exist in harmony. The NCA became a Man and Biosphere Reserve in 1971 and was declared a World Heritage Site by UNESCO in 1979. The area contains over 25,000 large animals including black rhinoceros. There are wildebeests, zebras, eland and Grant's and Thomson's gazelles. The crater also has the densest known population of lions, numbering 62. Higher up, in the rainforests of the crater rim, are leopards, about 30 large elephants, mountain reedbuck and more than 4,000 buffalos, spotted hyenas, jackals, rare wild dogs, cheetahs, and other felines. Originally part of the Serengeti National Park when the latter was established by the British in 1951, in 1959 the Ngorongoro Conservation Area Authority (NCAA) was formed, separating NCA from Serengeti. Land within the area is multi-use, providing protection status for wildlife while also permitting human habitation. Its uniqueness lays in the fact that the NCA is where man, livestock and wild animals live in peace: Maasai cattle can sometimes be seen grazing alongside zebras on Ngorongoro's grassland.