Orangutans

The Orangutan Species Survival Plan® manages the genetic and demographic health and oversees the care of orangutans in AZA zoos.

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Orangutans
Ape Overview \| Gibbons/Siamangs \| Bonobos \| Chimpanzees \| Gorillas \| Orangutans
Bornean orangutan \| Sumatran orangutan

Bornean orangutan Pongo pygmaeus The Bornean orangutan is divided into three subspecies: the northwest Bornean orangutan (P. p. pygmaeus); the central Bornean orangutan (P. p. wurmbii), which is the largest subspecies, and the northeast Bornean orangutan (P. p. morio), which is the smallest subspecies.

Natural History
The Bornean orangutan resides on the island of Borneo in Central Kalimantan (Indonesia) and Sabah, West and East Kalimantan, and Sarawak (Malaysia) in peat-swamp forests and flood plains. Bornean orangutans enjoy eating high-energy, sugary fruits. They are opportunistic foragers, and thus they have very flexible diets that change with the seasons. When fruit and figs are not available, orangutans eat bark, leaves, gingers, and stems.

Home ranges vary in size. Male home ranges are two to three times larger than those of females. Dominant males maintain relatively small home ranges.

Females reach maturity between ages 11 and 15 and give birth approximately every eight years. Once males become 'flanged', or develop cheek pads, they are mature and preferred as mates for matured females. Offspring are dependent for 7-10 years, which is the longest for any animal species other than humans.

It has been observed that some Bornean orangutans use leaves or a pile of twigs to shield themselves from the sun or rain. Despite this limited tool use observed in the wild, captive Bornean orangutans are very proficient tool users. Like the other apes, Bornean orangutans make night nests before going to sleep. The nests are arboreal and made of materials such as branches, leaves, and twigs.

Social Behavior
Orangutans, both Sumatran and Bornean, maintain loose communities or clusters of males and females. Mother-infant bonds are the strongest and weaken with the offspring's age. Males either move to a new community or wander between communities once they have become independent. Flanged males do not tolerate each other, but they are tolerant of subadult males. Relatively high food abundance in some parts of the Sumatran orangutans' range enables greater levels of sociality than has been observed among Bornean orangutans.

In both species, long calls enable adult males to notify females and other orangutans of their location over long distances. It is thought that the cheek pads on adult males help them direct their calls.

Threats and Conservation
Bornean orangutans are considered endangered by the International Union for the Conservation of Nature (IUCN). In 2004, it was estimated that there are between 45,000-69,000 Bornean orangutans. Although the habitats of the orangutans are technically protected, the majority of threats faced by the Bornean orangutans include: deforestation, logging and the production of timber, the production of palm oil, forest fires, and hunting.

Sumatran orangutan
Pongo abelii
Currently only a single species of Sumatran orangutan is recognized.

Natural History
Sumatran orangutans live on the island of Sumatra in Indonesia and are most abundant in the forests of flood plains, alluvial bottomlands, and freshwater and peat swamps. Orangutans live best in areas with low human populations. Most Sumatran orangutans live below 1,000 meters. Current distribution is primarily determined by the availability of preferred fruits and human presence.

Ranging patterns differ between Sumatran orangutans. There are three classes of ranging behavior: 'resident', 'commuter', and 'wanderer'. Male home ranges are two to three times larger than female's. Dominant males maintain relatively small home ranges.

Sumatran orangutans can be prolific tool users and have been documented to use multiple types of tools, primarily for extracting food and protecting themselves from sun or rain. Tool use is most prevalent in populations where food is abundant and thus permits larger associations and high levels of social tolerance. This suggests that orangutan tool use behavior is socially transmitted and represents an example of culture. Like the other apes, Sumatran orangutans make night nests before going to sleep. The nests are arboreal and made of materials such as branches, leaves, and twigs.

In both species, long calls enable adult males to notify females and other orangutans of their location over long distances. It is thought that the cheek pads on adult males help them direct their calls.

Threats and Conservation The Sumatran Orangutan is considered Critically Endangered by the International Union for the Conservation of Nature (IUCN). In 2002, it was estimated that only 7,300 Sumatran orangutans remained. Threats include: hunting, international trade, forest fires, forest fragmentation, timber production, and logging.