The Singapore Zoo, formerly known as the Singapore Zoological Gardens and commonly known locally as the Mandai Zoo, occupies 28 hectares (0.28 km²) of land on the margins of Upper Seletar Reservoir within Singapore's heavily forested central catchment area. The zoo was built at a cost of S$9m granted by the government of Singapore and opened on 27 June 1973. It is operated by Wildlife Reserves Singapore, who also manage the neighbouring Night Safari and the Jurong Bird Park. There are about 315 species of animal in the zoo, of which some 16% are considered threatened species. The zoo attracts about 1.6 million visitors each year.
From the beginning, Singapore Zoo followed the modern trend of displaying animals in naturalistic, 'open' exhibits with hidden barriers, moats, and glass between the animals and visitors. It houses the largest captive colony of orangutans in the world. In 1977, primatologist Dr Francine Neago lived inside a cage with eighteen orangutans for six months to study their behavior and communication.