Sumatran Orangutan - portrait of an adult lying comfortably on a tree branch in a sumatran rainforest. (Pongo abelii). Gunung Leuser National Park, Sumatra, Indonesia. Many of the orang utans in Gunung-Leuser National Park are from a rehabilitation centre, which nursed orphaned and ill orang utans back to health and released them in the wild. The rangers of the national park still have one place, where they feed some of the released animals who choose to return to the site, so they can be seen close-up.