Orangutans

Orangutans share a preference with humans for fertile alluvial plains and lowland valleys – a habitat once rich in tropical forests but now disappearing fast due to logging and agricultural schemes.

The two species are each confined to just one island: Sumatra and Borneo. With numbers having fallen drastically over the past century, and human pressure only increasing, orangutans may be lost from the wild forever within a few decades.

• More on the Sumatran orangutan
• More on the Bornean orangutan

Physical description 

Orangutans are the largest tree-climbing mammal. They have a characteristic ape-like shape, shaggy reddish fur and grasping hands and feet, with very long arms that may reach 2 m in length. Legs are relatively short and weak, but the hands and arms are powerful.

There are 2 different types of adult male orangutan: "flanged" & "unflanged". Flanged males have a long coat of dark hair on the back, a facial disk, flanges and a throat sac used for “long calls". The unflanged male looks like an adult female. Both reproduce and an unflanged male can change to a flanged male for reasons that are not yet fully understood. Orangutans are the only primate in which this biological phenomenon occurs.

Size: 1.25-1.5m in length;  females weigh 30-50kg, males weigh 50-90kg

Colour: Reddish brown

The 'man of the forest'

Orangutans live in primary and secondary forest. Although they can occur up to 1,500m above sea level, most are found in lowland areas and prefer forests in river valleys or floodplains – usually lowland dipterocarp, freshwater and peat swamp forests.

Orangutans travel about by moving from one tree to another, and usually avoid climbing down to the ground - although there are differences between the two species. When on the ground, they move on "all fours", with the clenched fist placed on the ground.

Orangutans make a nest of vegetation to sleep in at night, with smaller ones made during the day to rest.

Social structure
Adult orangutans are generally solitary, although temporary aggregations are occasionally formed. The large home ranges of males overlap the ranges of several adult females. Adult males are generally hostile to one another, although they do not display territoriality. 

Life cycle
Orangutans usually give birth to a single young, or occasionally twins. 

After weaning at about 3.5 years of age, young individuals become gradually independent of their mother after she gives birth to a second young. 

Orangutan females first reproduce at around 10-15 years of age, depending on the species/subspecies. Females give birth probably not more than once every 5 years, and the interbirth interval can be as long as 10 years.

The long time taken to reach sexual maturity, the long interbirth periods, and the fact that orangutans normally give birth to just a single young mean that orangutans have an extremely low reproductive rate. This makes orangutan populations highly vulnerable to excessive mortality, and means that populations take a long time to recover from population declines. 

Diet
About 60% of the orangutan's diet includes fruit (e.g. durians, jackfruit, lychees, mangosteens, mangoes and figs), while the rest comprises young leaves and shoots, insects, soil, tree bark, woody lianas, and occasionally eggs and small vertebrates. They obtain water not only from fruit, but also from tree holes. 

Population & distribution

Previous population & distribution
Pleistocene fossil records in southern China, northern Vietnam, Lao PDR, and Java indicate that the genus once had a  wide distribution in southeast Asia.

Orangutans are now only found on the islands of Borneo and Sumatra, with populations on each island belonging to separate species. A century ago there were probably more than 230,000 orangutans in total.

Current population & distribution
Both orangutan species have experienced sharp population declines over the past few decades.

Their dense forest home makes it difficult to precisely determine population sizes; however the Bornean orangutan is estimated to number about 41,000 individuals, while the Sumatran orangutan is estimated to number about 7,500 individuals.

• More on the Sumatran orangutan
• More on the Bornean orangutan

What are the main threats?

Habitat loss
Habitat destruction and fragmentation is by far the greatest threat to orangutans.

Huge tracts of forest have been cleared throughout the their range, through legal and illegal logging and forest conversion for oil palm plantations and other agriculture. Fires related to these activities also pose a serious threat to both orangutans and their habitat.

Today, more than 50% of orangutans are found outside of protected areas, in forests under management by timber, palm oil and mining companies.

Hunting & illegal trade
Orangutans are an easy target for hunters, being large and slow targets. 

The animals are killed for food in some areas, or in retaliation when they move into agricultural areas and destroy crops. This occurs more in times of environmental stress when orangutans can't find the food they need in the forest.

Females in particular are most often hunted. When caught with offspring, the young are often kept as pets.

This pet trade is a major problem. It is thought that for each orangutan reaching Taiwan, as many as 3-5 additional animals die in the process. Recent enforcement of the law in Taiwan has reduced the importation of orangutans, but the trade remains a threat in Indonesia where there is still demand for orangutans as pets.

There is also trade in orangutan skulls in Kalimantan (Indonesian Borneo). 

• More on threats to Sumatran orangutans
• More on threats to Bornean orangutans
• More on habitat loss and degradation
• More on wildlife trade

You can help

• Adopt an orangutan through WWF-UK or WWF-US and support our work to protect orangutans (international adoptions possible)

• Buy sustainable wood, paper and palm oil. By purchasing certified sustainable palm oil and FSC-certified forest products, consumers, retailers, traders, and manufacturers help protect orangutan habitat by limiting illegal logging and forest conversion to oil palm plantations. 
   
• Spread the word! Click on the button to share this information with others via email or your favourite social networking service.