The Sumatran orangutan, Pongo abelii, is found only on the island of Sumatra, Indonesia. Fig. 1.1 shows a Sumatran orangutan. [Figure 1.1] (a) The International Union for Conservation of Nature (IUCN) is the world's largest global environmental organisation. The IUCN Red List of Threatened Species™™ evaluates the conservation status of plant and animal species. The Sumatran orangutan is categorised as critically endangered on the IUCN Red List. The Sumatran orangutan spends most of its time in trees and is very sensitive to habitat destruction. Table 1.1 shows the area of natural forest of Sumatra and the numbers of orangutans in 1985 and 2016. [Table 1.1] Table 1.1 | | 1985 | 2016 | | :---------------------- | :----- | :----- | | area of natural forest /million hectares | 25.3 | 12.4 | | number of orangutans | 25000 | 7300 |