Two Distinct Species

Previously found widespread across all of Asia’s tropical rainforests, orangutans can now only be found on two Southeast Asia islands, Borneo and Sumatra. They are classified into two genetically distinct species: the Bornean orangutans and the Sumatran orangutans. While both species have slight appearance and behavioural differences, they face a similar fate of being endangered as a result of poaching and habitat loss.

Do you know what are the differences between the two species?

Bornean Orangutan

Source: The Orangutan Foundation (UK)

Source: The Orangutan Foundation UK

With a population decline by more than 50% over the past 60 years, the Bornean Orangutan (Pongo Pygmaeus) is classified as endangered under the IUCN (International Union for Conservation of Nature) Red List. Its population is now estimated to be between 45,000 to 69,000.

Its natural habitats, inclusive of lowland rainforests and tropical, swamp and mountain forests, has also diminished by at least 55% over the last 20 years.

In general, Bornean orangutans weighs approximately 66 – 220 pounds and is about 3.3 – 4.6 feet tall. As compared to its Sumatran relatives, the Bornean species have darker hair, shorter facial hair and a wider face.

Three subspecies of the Bornean species have also been identified. Northwest Bornean orangutans are the most threatened subspecies as a result of habitat destruction and loss inflicted by logging and hunting. It is estimated that there are only about 1,500 of them left. Northeast Bornean orangutans have the smallest physique. They can be found in Sabah and eastern Kalimantan. Central Bornean orangutans are forms the majority of the Bornean orangutan population, with an estimate of more than 35,000 individuals.

Sumatran Orangutan

Source: The Orangutan Foundation UK

Source: The Orangutan Foundation UK

The Sumatran orangutan (Pongo Abelii) is classified as critically endangered under the IUCN Red List. At present, its population size is estimated to be approximately 7,300. An individual weighs about 66 – 198 pounds, and can grow up to about 4 – 5 feet tall.

In the past, the Sumatran species can be found throughout the entire island of Sumatra, extending into Java. However, they can now only be found in the North of the island with a majority in North Sumatra and Aceh.

Unlike its Bornean cousins, the Sumatran orangutans live almost exclusively in the trees of tropical and subtropical moist broadleaf forests. Female sumatrans more or less never descend to the ground, and adult males only do so rarely. In comparison, the Bornean species can often be found travelling on the ground.

The Sumantran orangutans have also been found to have more intimate social relationships and display of tool use. Also, adult males are often seen in solitary, while the females are found in the company of its offsprings. Also, whitish hair lacking in Bornean individuals, can often be found on the face and groin of the Sumatran species.

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