In May 2009, Usha and I visited the Gunung Leuser National Park in north Sumatra to see orangutans in the wild. We hired a guide in the gateway village of Bukit Lawang and hiked several miles into a dense primary growth forest. Heavy rain on the previous night made the hike rather treacherous and we had to grab on to branches and roots to go up and down the hilly terrain. But the forest was beautiful, abundant with tropical flora and fauna (some of it unique to the island), rushing streams and animal sounds, and we did get lucky: we saw about ten orangutans on our daylong hike. One middle-aged female—rescued years ago by the orangutan center in Bukit Lawang and reintroduced into the wild—even came down and held Usha's hand! Other primates we saw include gibbons and Thomas's Leaf-monkeys.
The orangutan (“person of the forest”), whose habitat has shrunk to parts of Sumatra and Borneo, has cognitive abilities that rival those of the gorilla and the chimpanzee, the only primates more closely related to humans. Placid, deliberate, and mostly vegetarian, orangutans are known for their ingenuity and persistence, particularly in manipulating mechanical objects, and for their "cognitive abilities such as causal and logical reasoning, self-recognition in mirrors, deception, symbolic communication, foresight, and tool production and use. In the wild, orangutans use tools, but at only one location in Sumatra do they consistently make and use them for foraging, [defoliating] sticks ... to extract insects or honey from tree holes and to pry seeds from hard-shelled fruit." (source) We saw one juvenile male using a stick as a tool.