A successful reintroduction program has brought Pileated gibbons back to the forests surrounding the ruins. (more info)

Named in OUV Crit X. Western Hoolock Gibbon (Hoolock hoolock).

OUV Crit X: the endemic Javan gibbon (Mylobates moloch)

Gunung Leuser is home to the Siamang, the largest of all gibbon species. They are known for their massive throat sacs that inflate to produce booming calls audible for miles.

A white‐handed gibbon (Hylobates lar) population of at least 4,000 individuals in Huai Kha Khaeng Wildlife Sanctuary (source)

OUV Crit X: the largest remaining population of Southern White-cheeked Gibbon

Lar gibbons are frequently seen along the main access road leading to the higher elevations, especially in the early morning.

Arguably, the best place in the world to see wild gibbons. Because the park has been a research site for decades, the gibbons are habituated to humans. You can often see Lar gibbons right along the roads or from the park’s main hiking trails. OUV: "The unique overlap of the range of two species of gibbon, including the vulnerable pileated gibbon, further adds to the global value of the complex."

Hoolock Gibbon (Hoolock hoolock)