The Sumatran orangutan is nearly exclusively arboreal, living among the trees of tropical rainforests. Females virtually never travel on the bottom and adult males do so rarely. Sumatran orangutans are reported to possess closer social ties than their Bornean cousins. This has been attributed to mass fruit on fig trees, where groups of Sumatran orangutans can close to feed. Adult males are typically solitary while females are amid offspring.
Historically, the Sumatran orangutan was distributed over the whole island of Sumatra and further south into Java. The species’ range is now restricted to the north of the island with a majority within the provinces of North Sumatra and Aceh. Of the nine existing populations of Sumatran orangutans, only seven have prospects of long-term viability, each with an estimated 250 or more individuals. Only three populations contain quite 1,000 orangutans. Orangutans that were confiscated from the illegal trade or as pets are being reintroduced to Bukit Tigapuluh park. They number around 70 and are reproducing.