along the Mbagathi River give the park more water resources than these outside areas. They attract water dependent herbivores during the dry season. The park is the northern limit for wildlife migrations in the dry season. The park has a high diversity of bird species, with up to 500 permanent and migratory species in the park. Dams have created a man-made habitat for birds and aquatic species. The David Sheldrick Trust runs a sanctuary in the park that hand-rears orphaned elephant and rhinoceros calves, and later releases them back into secure sanctuaries. Orphaned and sick animals are brought to the sanctuary from all over Kenya. The sanctuary is located close to the park's main entrance. It was opened in 1963. It was set up by Daphne Sheldrick after the death of her husband David Sheldrick, the anti-poaching warden of Tsavo National Park. Nairobi National Park is sometimes called Kifaru Ark, which means "Rhinoceros Sanctuary". It is one of Kenya's most successful rhinoceros sanctuaries, and it is one of only a few parks where visitors can be certain of seeing a black rhinoceros in its natural habitat. Conservation Mervyn Cowie oversaw the development of several of Kenya's national parks and designed them with human visitors in mind. This emphasis helped to make tourism Kenya's primary industry. However, it exacerbated problems between the human population and wildlife. Farmers living next to the parks did not have input into the establishment of the parks. Locals received very little benefit from the game animals. Livestock is threatened by lions, and some landowners think that Kenya's wildlife is not good for them. In 1948, 188,976 people lived in Nairobi, and by 1997 the city's population had grown to 1.5 million. The park is under pressure from the city's growing population and need for farmland. People live right next to the park's boundaries, which creates human-animal conflicts. The human population also creates pollution and garbage. Effluent and industrial waste from factories located along the park's northern boundary contaminate the park's surface and ground water systems. Treaties with the Maasai in 1904 and 1911 forced them to give up all of their northern grazing lands on the Laikipia escarpment near Mount Kenya. Some of the people that lost land there were resettled in the Kitengela area. The Maasai's pastoral life did not create any conflicts with the wildlife. Today the Kitengela's former Maasai group-ranches have been privatized