Sumatran Orangutan Pongo abelii Lesson, 1827 Indonesia (Sumatra) (2000, 2002, 2004, 2006)

Sumatran and Bornean (Pongo pygmaeus Linnaeus, 1760) orangutans, now recognized as two distinct species, comprise the genus Pongo. While there are considered to be three subspecies of P. pygmaeus, the Sumatran orangutan is regarded as a single taxonomic unit. The viability of all taxa is in question, but the Sumatran orangutan faces a more immediate extinction risk than the Bornean, and is considered Critically Endangered. The species is endemic to Sumatra, Indonesia, and is now entirely restricted to remaining lowland forests in Nanggroe Aceh Darussalam (NAD) and North Sumatra Provinces. About 7,000 individuals remain (based largely on 2002 satellite imagery), surviving in 13 fragmented habitat units stretching from northern NAD, south to the Batang Toru River in North Sumatra, with a notable gap in their distribution immediately west of Lake Toba. The southernmost populations may be genetically and culturally distinct from their more northern relatives. The largest populations live within NAD province, where until recently, a separatist conflict made monitoring and conservation work problematic. By far the most significant populations, totaling about 5,600 animals, are found within the Leuser Ecosystem, a 26,000 km˛ conservation area established by presidential decree that encompasses the smaller Gunung Leuser National Park (10,950 km˛; itself part of the Sumatran Rainforest World Heritage Site) and the 1,025 km˛ Singkil Swamps Wildlife Reserve within its boundaries. The Ecosystem and the national park within it form the only conservation area of note where viable wild populations of the Sumatran orangutan, Sumatran tiger, Sumatran rhinoceros and Sumatran elephant, each of which is endangered in itself, still occur living side by side. The National Park, however, is predominantly high mountains, and as the orangutan is a predominantly lowland creature, rarely being found above 1,000 m asl, the majority occurs within the larger Leuser Ecosystem but outside the National Park. For example, the Ecosystem harbors c.75% of the remaining 7,000 Sumatran orangutans whilst only 24% are found within the National Park and 20% within the Singkil Swamps Wildlife Reserve. Throughout its range, the primary threat to Sumatran orangutans is logging, both legal and illegal, which often leads to total conversion of forests for agriculture or oil palm plantations. Although exact figures are still unavailable, primary lowland forests in Sumatra have been devastated over the last 20 years. One analysis of satellite imagery concluded that habitat supporting around 1,000 orangutans was being lost each year in the Leuser Ecosystem alone during the late 1990s (van Schaik et al. 2001). This was largely due to legal logging concessions and conversion of lowland forests to palm oil estates, but also illegal logging and encroachment in some places. Fortunately, however, the rate of habitat loss decreased markedly in many areas during the Aceh civil conflict, as activities in the forests became unsafe, and as a result of a moratorium imposed on logging in the province by the Aceh government. Orangutan populations have nevertheless plummeted in regions that have been affected by logging. Even small scale illegal logging can reduce local orangutan densities by as much as 60% in Sumatra (Rao and van Schaik 1997). At least six of the remaining seven populations containing over 250 individuals have experienced between 10 and 15% annual habitat loss due to logging. Encroachment and conversion, especially by settlers fleeing the conflict in NAD and migrants from Nias Island, have accelerated habitat loss in some parts. Relocation of people from coastal areas and an increase in demand for timber after the 2004 tsunami poses a significant new threat. Several proposed new roads (known as the Ladia Galaska project) will lead to a major increase in fragmentation of remaining orangutan populations. Throughout their range orangutans are sometimes killed as pests along forest edges as they raid agricultural crops, and in the far south of their range they are occasionally still hunted as food. A small but significant pet trade in young Sumatran orangutans also persists. Key conservation interventions rely heavily on a dramatic and rapid improvement in enforcement of wildlife and forest laws and far greater consideration for environmental issues in spatial planning decisions. Implementing patrols, improving law enforcement, stopping illegal logging, halting legal logging and forest conversion to plantations, promoting forest restoration, halting road construction, addressing human-orangutan conflict, and providing connectivity in the landscape to allow for genetic exchange are all seen as pre-requisites for the species’ survival. If current rates of habitat loss persist a further 50% of Sumatran orangutans will vanish within a decade. However, there is as much reason to believe the rate of decline will actually increase due to higher demand for timber, fragmentation by roads, expansion of plantations and general population pressure, as there is for mitigation of these threats. Solutions to conserve the remaining lowland primary forests are urgently needed. Ian Singleton, Susie Ellis & Mark Leighton

References Ellis, S., Singleton, I., Andayani, N., Traylor-Holzer, K. and Supriatna, J. (eds.). 2006. Sumatran Orangutan Conservation Action Plan. Conservation International, Jakarta, Indonesia, and Washington, DC. IUCN. 2004. 2004 IUCN Red List of Threatened Species. IUCN: The World Conservation Union, Gland. Rao, M. and van Schaik, C.P. 1997. The Behavioural ecology of Sumatran orangutans in logged and unlogged Forest. Trop. Biodiv. 4(2): 173–185. Rijksen, H. D. 2001. The orangutan and the conservation battle in Indonesia. In: Great Apes and Humans: The Ethics of Co-existence, B. B. Beck, T. S. Stoinski, M. Hutchins, T. L. Maple, B. Norton, A. Rowan, E. F. Stevens and A. Arluke (eds.), pp.57–70. Smithsonian Institution Press, Washington, DC. Rijksen, H. D. and E. Meijaard. 1999. Our Vanishing Relative: The Status of Wild Orangutans at The Close of The Twentieth Century. Kluwer Academic Publishers, Dordrecht. Singleton, I., S. Wich, S. Husson, S. Stephens, S. Utami Atmoko, M. Leighton, N. Rosen, K. Traylor-Holzer, R. Lacy and O. Byers (eds.). 2004. Orangutan Population and Habitat Viability Assessment: Final Report. IUCN/SSC Conservation Breeding Specialist Group (CSG), Apple Valley, MN. Van Schaik, C. P., K. A. Monk and J. M. Y. Robertson. 2001. Dramatic decline in orangutan numbers in the Leuser Ecosystem, northern Sumatra. Oryx 35(1). Wich, S. A. and M. L. Geurts. 2001. Orangutan Surveys in Sumatra Utara, Riau and Sumatra Barat. Survey Report to the Golden Ark Foundation, The Netherlands. Suggested citation: Singleton, I., Ellis, S. and Leighton, M. 2007. Sumatran Orangutan, Pongo abelii Lesson, 1827. In: Primates in Peril: The World’s 25 Most Endangered Primates 2006–2008, R. A. Mittermeier et al. (compilers), pp.18-19. Unpublished report, IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), and Conservation International (CI), Arlington, VA.