The Singapore Zoo, formerly known as the Singapore Zoological Gardens and commonly known locally as the Mandai Zoo, occupies 28 hectares (69 acres) on the margins of Upper Seletar Reservoir within Singapore's heavily forested central catchment area. The zoo was built at the cost of $9 million granted by the government of Singapore and opened on June 27, 1973. It is operated by Wildlife Reserves Singapore, who also manages the neighboring Night Safari, River Safari, and the Jurong Bird Park. There are about 315 species of animal in the zoo, of which some 16 percent are considered to be threatened species. The zoo attracts 1.7 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.