The name orangutan translates from the Malay language to “person of the forest,” a fitting name for a primate that shares 97% of human DNA. These great apes are the only ones found exclusively in Asia and are recognized for their intelligence and distinct reddish-brown fur. Their unique characteristics and behaviors have captivated observers for centuries.
Orangutan Species and Habitats
There are three distinct species of orangutan, each geographically isolated and adapted to its island environment. The Bornean orangutan (Pongo pygmaeus) is from the island of Borneo and is found in lowland tropical rainforests and peat swamp forests. This species is slightly larger than its cousins and more likely to spend time on the ground.
The Sumatran orangutan (Pongo abelii) resides on the northern part of the Indonesian island of Sumatra. These orangutans inhabit tropical montane and swamp forests, preferring the dense canopy. They are distinguished by longer facial hair and have closer social bonds than Bornean orangutans.
A third species, the Tapanuli orangutan (Pongo tapanuliensis), was recently identified and is the most endangered of all great apes. This small, isolated population of fewer than 800 individuals lives in an upland area in North Sumatra. The Tapanuli orangutan is differentiated by its skull and teeth structure, as well as frizzier hair.
Arboreal Lifestyle and Diet
Orangutans are the world’s largest tree-dwelling mammals, spending nearly their entire lives in the forest canopy. Their bodies are adapted for this arboreal existence, with long, powerful arms that can reach two meters in length and hook-like hands and feet for gripping branches. This allows them to move through the trees using a method known as quadrumanous locomotion, using all four limbs.
Each night, orangutans construct a new nest high in the trees to sleep in. These nests are structures made from woven branches and leaves, providing a secure platform from ground-based predators. This construction is a learned skill, with young orangutans observing their mothers to master the technique.
As primarily frugivores, about 60% of an orangutan’s diet consists of fruit. They have a strong memory for the locations of fruit trees, a necessary skill as different trees fruit at different times. Wild figs and durians are favorites, but they also consume leaves, shoots, bark, soil, and insects to supplement their diet.
Social Behavior and Reproduction
Unlike other great apes that live in large social groups, orangutans are semi-solitary. This behavior is influenced by their diet, as the scattered availability of fruit in the rainforest cannot support large gatherings. While adults forage alone, they are not strictly antisocial and may interact with others in areas with abundant food.
The most significant social bond is between a mother and her offspring. A young orangutan will stay with its mother for six to eight years, a longer period than any other great ape. During this extended childhood, the mother teaches her young everything needed for survival, from finding food and building nests to navigating the social world.
This long dependency results in a slow reproductive rate, with females giving birth only once every eight years on average. This is the longest interbirth interval of any mammal, which affects the species’ ability to recover from population declines.
Adult males are solitary and can be categorized as flanged or unflanged. Flanged males are larger, with prominent cheek pads and a large throat sac. They use this sac to produce loud “long calls” to attract females and intimidate rivals.
Threats to Survival
The primary threat to all three orangutan species is the loss of their rainforest habitat. The islands of Borneo and Sumatra have experienced high rates of deforestation over the past several decades. This destruction is driven by clearing land for agriculture, with the expansion of palm oil plantations being a major factor.
Logging, both legal and illegal, and mining operations also contribute to the fragmentation of their forest homes. Because orangutans cannot swim, they become isolated in shrinking patches of forest, limiting their access to food and mates. This habitat loss directly impacts their ability to survive and reproduce.
The illegal pet trade poses another serious threat, where young orangutans are captured for sale. This practice is damaging because the mother is almost always killed to take her infant. Poaching for meat also occurs in some areas. Due to these pressures, the International Union for Conservation of Nature (IUCN) lists all three species as Critically Endangered, with the Bornean orangutan population estimated at around 104,700 and the Sumatran at less than 14,000.