The orangutan is the only member of the great ape family found in Asia. All other members of the great ape family are located in Africa; chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla and Gorilla beringei), and bonobo (Pan paniscus). There are two species of orangutan, the Bornean orangutan (Pongo pygmaeus) distributed across the island of Borneo in Indonesia (Kalimantan) and Malaysia (Sabah and Sarawak, and the Sumatran orangutan (Pongo abelii) situated on the Indonesian island of Sumatra.
The two species have been geographically separated for at least 8,000 years when increased sea levels isolated the two islands. Based on scientific research investigating genetics, morphology, ecology, behaviour and life history, Sumatran and Bornean orangutans demonstrate significant differences (Delgado & van Schaik, 2000; Groves, 2001; Zhang et al., 2001). Overall physical characteristics
- The Bornean orangutan (Pongo pygmaeus) has a larger body size, and has dark or reddish brown short hair;
- The Sumatran orangutan (Pongo abelii) has a smaller body size, with brighter orange hair
- In both species, male orangutans are much larger than the females, typically two to three times heavier.
- Male orangutans develop large cheek pads (flanges) which develop post-sexual maturity
The Bornean orangutan is classified into 3 sub-species (Groves, 2001; Warren et al., 2001): Pongo pygmaeus pygmaeus, ranging from northwest Kalimantan (including Betung Kerihun and DanauSentarum National Parks) north of the Kapuas river, across the east of Sarawak state (Malaysia) Pongo pygmaeus wurmbii, ranging from south of Kapuas river in West Kalimantan to east of the Barito river in Central Kalimantan Pongo pygmaeus morio ranging throughout Sabah and East Kalimantan south to the Mahakam river.
Habitat and Behaviour
Bornean orangutans inhabit lowland tropical dry-land and swamp forests up to 500 m above sea-level, occasionally ranging higher or in degraded habitats. Orangutans are the largest arboreal animal, i.e. creatures that spend most of their time in the trees and complete their life-history in the trees.
However orangutans, particularly males, do spend time foraging or travelling on the ground. Orangutans build a new sleeping platform, or ‘nest’, high in the trees each night by bending branches into a bowl and filling with foliage.
Orangutans are predominately frugivorous, with over 100 types of fruit typically recorded in their diet from any one site. However they have a very wide diet which includes flowers, leaves, the cambium layer of bark; the inner pith of rattans, pandans, gingers and palms; termites, ants and other invertebrates; honey, fungi and on very rare occasions have been observed to eat small mammals.
They need to rely on these foods during periods of fruit-shortage and also develop large fat reserves to help them through extreme periods of food shortage, or ‘fruit-crunch periods. Orangutans are important dispersal agents of fruit seeds, either by passing seeds through their digestive tract or by carrying and discarding seeds as they move through the trees, thus playing a key role in forest ecology and regeneration.
Orangutans are essentially solitary with the only permanent bond being between mother and infant. However they do live in very loose clusters of related females, which occasionally meet in twos and sometimes more during periods of higher food-availability to allow bonds to be maintained, infants to play and learn together and novel behaviours to be shared.
Males disperse away from their natal range to prevent inbreeding and become sexually mature at around 15 years of age. Between 18 and 20 years old they grow much larger and develop secondary sexual characteristics of cheek flanges and large throat sac, which they use to make booming long calls to attract females and warn-off other males.
Males compete to become dominant, although non –dominant males do father a large proportion of infants, particularly unflanged males aged 15-20 who have not attained full size and are able to forcefully mate females.
Female orangutans give birth to one infant at a time after 8 and a half months of pregnancy, and do not have another child until the first infant reaches seven years of age. This is the longest inter-birth interval known in the animal kingdom and enables the mother to give full attention to her offspring as it learns the skills needed to survive on its own, including making nests, recognising different kinds of food and avoiding predators.
Once it has learnt these skills it still stays with its mother for protection and to make a mental map of the forest, particularly to learn where all the important food resources are, until it is time to move away.
Orangutans are highly intelligent creatures with advanced problem-solving skills. They are able to make use of things in their environment for tools and medicines. They display cultural behaviours, with different populations tackling the same problem in different ways. They learn from other orangutans and pass on their own skills when they meet, which is more frequent when food availability is high.
The latest population estimate for Bornean orangutans derived at the International Population Habitat Viability Analysis (PHVA) Workshop in 2004, was approximately 55,000 individuals.
At the same time it was noted that populations are decreasing at a rapid rate owing to (1) forest conversion, particularly for oil-palm plantations and other forms of agriculture; (2) other forms of forest loss, particularly forest fires in drained peatland areas; (3) forest degradation by illegal logging and (4) hunting of orangutans for food and capture for the pet-trade.
Approximately one third of orangutans are found in conservation forests and the remainder are under severe threat. They are classified as Endangered by the International Union for Conservation of Nature and Natural Resources (IUCN) and protected under Indonesian Law against any kind of persecution of them or their habitat.
Nevertheless forest is still being cleared, logged or burnt and this has led to the death of many thousands of orangutans over the past decade and the displacement of many more. Some of these displaced orangutans have been rescued by Reintroduction Centres that aim to return them back to the wild once safe and secure forests are identified.