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Harper, Douglas. "Orangutan". Online Etymology Dictionary. Archived from the original on 4 November 2012 . Retrieved 4 May 2012.All three species are critically endangered according to the IUCN Red List of mammals. [115] [116] [117] They are legally protected from capture, harm or killing in both Malaysia and Indonesia, [118] and are listed under Appendix I by CITES, which prohibits their unlicensed trade under international law. [119] The Bornean orangutan range has become more fragmented, with few or no apes documented in the southeast. [116] The largest remaining population is found in the forest around the Sabangau River, but this environment is at risk. [120] The Sumatran orangutan is found only in the northern part of Sumatra, most of the population inhabiting the Leuser Ecosystem. [115] The Tapanuli orangutan is found only in the Batang Toru forest of Sumatra. [117] Deforestation for palm oil production in Indonesia Oaks, Elizabeth H. (2007). Encyclopedia of World Scientists: From Around the World. Facts on File. p.260. ISBN 978-0816041305. MacClancy, J.; Fuentes, A. (2010). Centralizing Fieldwork: Critical Perspectives from Primatology, Biological, and Social Anthropology. Berghahn Books. pp.6–7. ISBN 978-1-84545-690-0. Archived from the original on 30 April 2016 . Retrieved 16 December 2015. van Noordwijk, Maria A.; Sauren, Simone E.B.; Nuzuar; Abulani, Ahbam; Morrogh-Bernard, Helen C.; Atmoko, S. Suci Utami; van Schaik, Carel P. (2009). "Development of Independence". In Wich, Serge A.; Atmoko, S. Suci Utami; Setia, Tatang Mitra; van Schaik, Carel P. (eds.). Orangutans: Geographic Variation in Behavioral Ecology and Conservation. Oxford University Press. p.199. ISBN 978-0199213276. Martinelli, D. (2010). A Critical Companion to Zoosemiotics: People, Paths, Ideas. Springer. pp.218–19. ISBN 978-90-481-9248-9. Archived from the original on 30 April 2016 . Retrieved 16 December 2015.

Meijaard, E.; Buchori, B.; Hadiprakarsa, Y.; Utami-Atmoko, S. S.; etal. (2011). "Quantifying Killing of Orangutans and Human-Orangutan Conflict in Kalimantan, Indonesia". PLOS ONE. 6 (11): e27491. Bibcode: 2011PLoSO...627491M. doi: 10.1371/journal.pone.0027491. PMC 3214049. PMID 22096582. Birutė Galdikas wrote that orangutans were already threatened by poaching and deforestation when she began studying them in 1971. [121] By the 2000s, orangutan habitats decreased rapidly because of logging, mining and fragmentation by roads. A major factor has been the conversion of vast areas of tropical forest to palm oil plantations in response to international demand. Hunting is also a major problem, as is the illegal pet trade. [115] [116] a b Singleton, I.; van Schaik, C. P. (2002). "The Social Organisation of a population of Sumatran orang-utans". Folia Primatologica. 73 (1): 1–20. doi: 10.1159/000060415. PMID 12065937. S2CID 13557435. a b Didik, Prasetyo; Ancrenaz, Marc; Morrogh-Bernard, Helen C.; Atmoko, S. Suci Utami; Wich, Serge A.; van Schaik, Carel P. (2009). "Nest building in orangutans". In Wich, Serge A.; Atmoko, S. Suci Utami; Setia, Tatang Mitra; van Schaik, Carel P. (eds.). Orangutans: Geographic Variation in Behavioral Ecology and Conservation. Oxford University Press. pp.270–75. ISBN 978-0-19-921327-6. Archived from the original on 24 April 2016 . Retrieved 16 December 2015. O'Malley, R. C.; McGrew, W. C. (2000). "Oral tool use by captive orangutans ( Pongo pygmaeus)". Folia Primatologica. 71 (5): 334–41. doi: 10.1159/000021756. PMID 11093037. S2CID 19354930.

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a b van Schaik, C. P.; Preuschoft, S.; Watts, D. P. (2004). "Great ape social systems". In Russon, A. E.; Begun, D. R. (eds.). The Evolution of Thought: Evolutionary Origins of Great Ape Intelligence. Cambridge University Press. pp. 193–94. ISBN 978-0521039925. Orangutans sometimes travel on the ground when going long distances because appropriate sized branches may not always be available. When on the ground, they use all four limbs, supporting themselves on the sides of clenched fists, or occasionally walk on upright on two legs. Orangutans also come down if there is a need to find food and water elsewhere, for example, if there is a drought or fire. Flanged males (males with flanges, also known as cheek pads) use long calls to attract females and to discourage the approach of other males. Throat sacs add resonance to long calls, which are specific to individual males. Orangutans of all ages and sexes give kiss squeak vocalizations, engage in branch-shaking displays and sometimes even uproot dead trees when confronted by unknown individuals or when they are not habituated to the presence of human observers. In zoos, displays consist of throwing around tubs and other objects. Turner, Dorie (12 April 2007). "Orangutans play video games (for research) at Georgia zoo". USA Today. Archived from the original on 2 July 2007 . Retrieved 12 April 2007.