Sumatran Orangutan

Range countries
Indonesia

Population status
The Sumatran orangutan (Pongo abelii) is one of the three species of orangutans and is native to the island of Sumatra, Indonesia. The most recent population estimate for the Sumatran orangutan stands at 13,846 individuals, inhabiting a total forest area of 16,775 km² (Wich et al. 2016). Considering only populations with over 250 individuals (deemed potentially viable in the long term) leaves 13,587 individuals. The majority, 95.0%, reside in the Leuser Ecosystem, while others are found in the Sidiangkat and Pakpak. This 2016 estimate surpasses the previous one of around 6,600 individuals, owing to improved survey techniques and expanded coverage rather than an actual increase. Notably, overall numbers continue to decline significantly (Singleton et al. 2023). Given the discovery of orangutans at altitudes up to 1,500 m asl in various areas, connectivity among subpopulations in the mountainous Leuser Ecosystem is likely better than previously believed (Wich et al. 2008). However, recent studies indicate genetic differentiation between subpopulations, partly attributed to geographic barriers like rivers and high mountain ridges, even within the Leuser Ecosystem (Nater et al. 2013). Apart from wild populations, two new Sumatran orangutan populations are emerging through the reintroduction of confiscated illegal pets—one around Bukit Tigapuluh National Park (Jambi and Riau provinces) and another around Jantho Pine Forest Nature Reserve in northern Aceh, with over 260 individuals reintroduced. The aim is to establish genetically-viable, self-sustaining wild populations as a safety net (Singleton et al. 2023).

Threats
The survival of the Sumatran orangutan faces serious threats primarily due to habitat loss and fragmentation caused by large-scale clearing of forests for oil-palm plantations and logging activities (Wich et al. 2008, 2011, 2016). The creation of new roads, often for illegal settlements and agriculture, poses additional risks by fragmenting populations and providing access to wildlife poachers. Industrial plantations force orangutans to seek refuge in remaining forest patches, leading to long-term challenges like malnutrition and starvation due to limited resources. The illegal pet trade and deliberate killings further jeopardize their existence, with human-wildlife conflicts arising from incidents like crop raiding (Wich et al. 2012). The most significant current threat stems from the government-ratified spatial land-use plan in Aceh Province, initiated in 2013. Despite obligations for Leuser Ecosystem conservation under Aceh's autonomy law, the plan neglects its existence, allowing the designation of vast orangutan habitats for plantations, timber, and mining concessions. Legal challenges seek to replace this plan with one complying with laws and providing proper protection for the Leuser Ecosystem. Until then, the 2013 Aceh plan legitimizes illegal roads, exacerbating fragmentation, hunting, and encroachment, posing severe risks to Sumatran orangutan populations (Singleton et al. 2023).

Conservation
Sumatran orangutan conservation involves a comprehensive approach, combining habitat protection, community engagement, and rehabilitation. National parks and reserves have been established to safeguard their habitats, with various organizations addressing deforestation root causes and advocating sustainable land use practices. Ensuring the long-term survival of the species requires protecting extensive areas of primary forest below 1,500 m asl. The Leuser Ecosystem, a key stronghold covering 26,000 km², supports approximately 95% of wild Sumatran orangutans. Conservation of the Leuser Ecosystem is mandated by Indonesian law, emphasizing its environmental function and calling for its recognition and integrity in all levels of spatial land-use planning. The 9,000 km² Gunung Leuser National Park, part of the Leuser Ecosystem and designated by UNESCO, supports 25.3% of Sumatra's orangutans (Singleton et al. 2023). Despite dense lowland forest areas outside the park, also part of the Leuser Ecosystem, no other formally-established conservation areas outside it harbor this endangered species.

References
Nater, A., Arora, N., Greminger, M.P., van Schaik, C.P., Singleton, I., Wich, S.A., Fredriksson, G., Perwitasari-Farajallah, D., Pamungkas, J. and Krützen, M. 2013. Marked population structure and recent migration in the critically endangered Sumatran orangutan (Pongo abelii). Journal of Heredity 104: 213.

Singleton, I., Wich , S.A., Nowak, M., Usher, G. & Utami-Atmoko, S.S. 2023. Pongo abelii (amended version of 2017 assessment). The IUCN Red List of Threatened Species 2023: e.T121097935A247631244. https://dx.doi.org/10.2305/IUCN.UK.2023-1.RLTS.T121097935A247631244.en. Accessed on 15 January 2024.

Wich, S.A., Meijaard, E., Marshall, A., Husson, S., Ancrenaz, M., Lacy, R., van Schaik, C., Sugardjito, J., Simorangkir, T., Traylor-Holzer, K., Doughty, M., Supriatna, J., Dennis, R., Gumal, M., Knott, C. and Singleton, I. 2008. Distribution and conservation status of the orangutan (Pongo spp.) on Borneo and Sumatra: how many remain? Oryx 42: 1–11.

Wich, S.A., Riswan., Jenson, J., Refisch, J. and Nelleman, C. 2011. Orangutans and the Economics of Sustainable Forest Management in Sumatra. UNEP/GRASP/PanEco/YEL/ICRAF/GRID-Arendal.

Wich, S.A., Fredriksson, G.M., Usher, G.F., Peters, H.H., Priatna, D., Basalamah, F., Susanto, W.W. and Kühl, H. 2012. Hunting of Sumatran orangutans and its importance in determining distribution and density. Biological Conservation 146: 163–169.

Wich, S. A., Singleton, I., Nowak, M. G., Utami Atmoko, S. S., Nisam, G., Arif, S. M., ... & Kühl, H. S. (2016). Land-cover changes predict steep declines for the Sumatran orangutan (Pongo abelii). Science advances, 2(3), e1500789.

Last updated January 2024