Geographic Distribution and Habitat
The Bornean orangutan is one of only three species of orangutans; each is classified as a great ape and together they are the only great apes native to Asia. Inhabiting the equatorial island of Borneo, which is the world’s third-largest island encompassing the countries of Indonesia (home to the greatest population), Malaysia, and Brunei, Bornean orangutans live in lowland and hilly tropical and subtropical rainforests at elevations up to 2,625 feet, or a half-mile (800 meters), above sea level. They make the rainforest canopy their home. (Sumatran orangutans, who inhabit the island of Sumatra, belong to the second orangutan species. Tapanuli orangutans, announced as a unique species in November 2017 and also from Sumatra, are the third.)
Size, Weight, and Lifespan
As the third-heaviest living primate, after the eastern and western gorillas, the Bornean orangutan is also the largest arboreal (tree-dwelling) mammal.
In an example of sexual dimorphism, when significant physical differences (beyond sexual organs) distinguish the male and female sex of a species, fully grown male Bornean orangutans are much larger than their female counterparts
Adult males stand about 3.2 feet tall (97 cm), and weigh between 132 to nearly 200 pounds (60 to 90 kg).
Adult females stand about 2.5 feet tall (78 cm), and weigh between 88 and 110 pounds (40 to 50 kg).
In the wild, Bornean orangutans live 35 to 45 years. Captive Bornean orangutans can live to 60 years.
What Does It Mean?
A cranky, ill-tempered individual.
Visit the Glossary for more definitions
A coarse, shaggy reddish coat, reminiscent of an overcoat plucked from a thrift store, covers the body of this extremely long-armed great ape. Bornean orangutans have a reach of 6.5 to 8 feet (2 to 2.5 m). Their dexterous hands and feet allow them to grasp tree branches with great agility and skill. Closely-set brown eyes peer out from an expressive, broad bare face that is black in adults and pinkish around the eyes and muzzle in younger Bornean orangutans. Some adult males sport prominent mustaches and beards. Ears, palms, and soles of feet are bare of hair.
In another example of sexual dimorphism, the faces of fully mature male Bornean orangutans are graced with flanges; that is, flappy cheek pads that apparently lady Bornean orangutans find irresistible. Males with flanges have an added advantage over unflanged males; they possess a repertoire of vocalizations which they emit in long notes (which can carry over a mile), announcing their virility to attract receptive females. Flanged males are also equipped with large throat sacks and are considerably larger in overall size than unflanged males. These sexually desirable male accouterments can take up to 20 years to develop and are associated with increasing testosterone levels.
Youngsters sport wiry and unkempt hair, big and soulful eyes, ears you want to gently tweak, and expressive faces that can melt a curmudgeon’s heart making these little ones the darlings of all great ape babies—including humans!
Overall, the diet of Bornean orangutans includes 400 to 500 different types of food. But they especially love their fruits, which comprise 60 percent of their diet, making these great apes a predominantly frugivorous species. Wild figs and durians (an odorous fruit with spiked protuberances) are their favorites. They also eat various leaves, shoots, tree bark, honey, insects, and bird eggs. And they intentionally eat soil and small rocks. This proclivity is a recognized behavior known as geophagy, common among other great ape species, and provides Bornean orangutans with minerals not found in their largely fruit-based diet. The practice also helps to absorb toxins and provides other intestinal benefits, including combating diarrhea.
Bornean orangutans’ natural instinct is to eat often—and a lot. In the wild, physical daily activity such as foraging and building nests helps them to burn calories and prevents them from becoming overweight. Captive Bornean orangutans, however, are more sedentary and at risk for becoming obese.
Behavior and Lifestyle
A typical day in the life of Bornean orangutans begins with two to three hours of eating, a noontime nap, afternoon travel, and nest-building during the early evening.
Their proficient use of tools, as exhibited by their superb engineering skills in building their nightly nests, their use of branches to test water depth and to poke termite holes when they are in the mood for a termite snack, and their ability to solve abstract problems (demonstrated in captive orangutan studies), have earned them the distinction of being considered one of the most intelligent nonhuman primates.
Independent and predominantly solitary creatures, when their home ranges overlap Bornean orangutans will socialize with one another—particularly when raiding a full fruit tree. The rainforest canopy is where they forage, thrusting their body weight from branch to branch, using their strong hands and feet to bend and cause trees to sway as they less-than-gracefully advance. The rainforest is also where they sleep. Each night, in a new location, they construct an elaborate nest high in the treetops using branches and foliage to create makeshift mattresses, pillows, and roofs to protect them from rain.
Although they spend most of their time in trees, Bornean orangutans do, on occasion, venture to the forest floor—more so than another Asian great ape, the Sumatran orangutan. And unlike great apes who walk on their knuckles, orangutans walk on their fists.
Orangutan means “person of the forest” in the native languages of Indonesia and Malaysia.
Orangutans share approximately 97 percent of their DNA with human primates.
The following three subspecies of the Bornean orangutan are currently recognized:
- Northwest Bornean orangutan (P. p. pygmaeus) inhabits the state of Sarawak, Malaysia, and the province of West Kalimantan, Indonesia.
- Northeast Bornean orangutan (P. p. morio) inhabits the state of Sabah, Malaysia, the province of North Kalimantan, Indonesia, and the province of East Kalimantan, Indonesia.
- Southwest Bornean orangutan (P. p. wurmi) inhabits the province of West Kalimantan and the province of Central Kalimantan, Indonesia.
Daily Life and Group Dynamics
Two fully-flanged adult males will do their best to avoid each other. But if they find themselves vying for the attention of a sexually receptive female, these encounters can turn violent. Male combatants might fight for a few minutes or an hour or longer, causing minor to severe injuries to the other. Missing fingers, healed scars on their faces and heads, or even a missing eye are common in nearly all fully-flanged males.
Fights between flanged males and unflanged males do not appear to be an issue in the wild (according to a scientific study that examined their scat to compare testosterone levels in still-developing males to fully flanged males). Fully flanged males likely do not generally regard the younger males as a threat.
Orangutan females possess a sense of decorum and civility. They rarely engage in the type of violent aggression as practiced by combating flanged males, therefore their bodies are unmarred by such war wounds.
Even though Bornean orangutans are mostly solitary, they communicate through vocalizations, including a variety of sounds (like the long note of flanged males and also deep, throaty grunts to announce the threat of danger). In addtion they use gestures, as humans do, to indicate a desire or to make a point. Facial expressions convey sadness, joy, confusion, levity, fear, and many other emotions shared with human primates.
Reproduction and Family
Of all mammal species, orangutans are the slowest to breed, with an eight-year interval between births. Females first give birth at about 15 years of age.
A female Bornean orangutan will seek out a dominant flanged male with whom to mate. However, should she be caught alone by an unflanged male, he will force himself upon her in copulation.
Females give birth to a single infant after a gestation period of 8-9 monthss. Mothers carry their babies constantly for the first 2 or 3 years of their lives and will nurse them for 6 to 7 years, They also teach foraging techniques to their young.
Orangutans are considered mature at 8 years old, and this is when males strike out on their own. Female orangutans, however, remain with their mothers until their teen years to learn essential parenting skills, so that they will be capable of raising their own young when they become mothers themselves. Fathers do not participate in child-rearing.
Bornean organutans are sometimes referred to as the gardeners of their forests. They help the rainforest ecology by dispersing seeds while dropping partially-eaten fruits and through their fecal matter as they travel through the forest, thanks to their large and varied frugivorous diet.
Conservation Status and Threats
In February 2016, the threat to all Bornean orangutans was up-listed from Endangered to Critically Endangered by the International Union for Conservation of Nature , appearing on the IUCN Red List of Threatened Species (IUCN, 2016). The species now shares this ignoble distinction with Asia’s other great apes, the Sumatran orangutan, which has been Critically Endangered since 2008, and the Tapanuli orangutan, which was discovered and listed as Critically Endangered in 2017.
Facing an “extremely high risk of extinction in the wild,” the foremost threat to the Bornean orangutan’s survival is habitat loss, particularly from the slashing and burning of forests to transform habitat into palm oil plantations.
The palm oil industry is directly linked to deforestation, habitat degradation, climate change, animal cruelty, and indigenous rights abuses in the countries where it is produced. According to the World Wildlife Fund, an area the equivalent size of 300 football fields of rainforest is cleared each hour to make way for palm oil production. This large-scale deforestation is pushing the Bornean orangutan, along with many other species, to extinction.
Political unrest in Indonesia, poverty, and starvation are additional contributors to the Bornean orangutan’s demise. These dire factors have led indigenous people to hunt these animals for food and capture for the illegal pet trade.
According to World Wildlife Fund, 45,000 to 69,000 Bornean orangutans remain in the wild. That number might seem like a lot, but consider that in 2010 only 59.6 percent of Borneo’s forests were suitable for orangutans. And populations are predicted to decline as much as 86 percent by 2025, should this downward trajectory of habitat loss continue.
While in theory, much of the Bornean orangutan’s habitat is protected by Indonesian, Malaysian, and Brunei governmental law, enforcement is difficult. Furthermore, populations living in small patches of forest are isolated from other Bornean orangutans, thereby prohibiting successful reproduction. And because female orangutans only give birth every 8 years, orangutan populations take years to restore after natural disasters and human encroachment.
International trade of Bornean orangutans is banned under its listing in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. Unfortunately, this law is openly flouted.
But there is some hope.
Founded in 1990, the Orangutan Foundation is a United Kingdom-based charity and is the foremost orangutan conservation organization working actively across the range of both orangutan species. Its primary focus is protecting forest habitat so that orangutans have the best chance of survival in the wild. The foundation also works with local communities to promote research and education, so that indigenous people recognize that orangutans are essential citizens, through their role as seed dispersers, who nourish the habitat that is shared by the Bornean people and these great apes.
The Great Ape Survival Project, or GRASP, is a United Nations initiative committed to ensuring the long-term survival of chimpanzees, gorillas, bonobos, and orangutans and their habitats in Africa and Asia. GRASP, based in Kenya, is comprised of 106 partners that include international organizations in conservation and environmental protection. Each partner possesses a specific expertise and certain resources that GRASP directs to saving primate species. GRASP’s Borneo-based partners include the Orangutan Foundation, International Animal Rescue, the Borneo Orangutan Survival Foundation, and the Borneo Nature Foundation.
World Orangutan Events is “a non-partisan initiative to promote orangutan conservation and welfare, as well as inter-organization cooperation.” Orangutan Caring Week and International Orangutan Day are two examples of this initiative’s world-wide events to raise awareness.
Rehabilitation and reintroduction of captive Bornean orangutans, rescued from the illegal wildlife trade, is an example of direct action in saving the species.
Written by Kathleen Downey, August 2016