(3,404 m asl) in Aceh (Map 2) and exert a major influence on rainfall patterns. Western regions receive much more rain than those in the east, as prevailing winds from the Indone- sian ocean are forced upwards, cooling rapidly and condens- ing water vapour, which then falls as precipitation (Whitten et al. 1987) (Map 3).
Critically endangered During the late Pleistocene (128,000-11,000 years ago) oran- gutans could be found as far north as southern China, and as far south as the Indonesian island of Java (Jablonski et al. 2000).
Today, orangutans are confined to the north-western part of Sumatra and to scattered populations throughout the island of Borneo (Wich et al. 2008).
Today there are estimated to be only approximately 6,660 Su- matran orangutans in the wild (Wich et al. 2008), compared to an estimated 85,000 in 1900 (Rijksen and Meijaard 1999), a reduction of some 92%. Te Sumatran orangutan is listed as Critically Endangered in the 2010 IUCN (International Un- ion for Conservation of Nature) Red List (IUCN 2010) and is included in the ”Top 25 World’s Most Endangered Primates