The Bornean orangutan (Pongo pygmaeus) is a type of orangutan found only on the island of Borneo. It is part of a group of great apes that live only in Asia and is the largest of the three species in the Pongo genus. This animal has a rough, reddish-colored fur and arms that can be up to 1.5 meters (4 feet 11 inches) long. It shows sexual differences—males are bigger than females and grow large cheek pads (called flanges), for example.

The Bornean orangutan lives in lowland and mountain rainforests on Borneo, up to an elevation of 1,500 meters (4,900 feet). It eats fruits, seeds, flowers, bird eggs, sap, and vines. This species is very smart, using tools and showing unique cultural behaviors. It is critically endangered, and threats like deforestation, palm oil farming, and hunting greatly endanger its survival.

Taxonomy

Bornean orangutans separated from Tapanuli orangutans about 674,000 years ago. Bornean and Sumatran orangutans split about 400,000 years ago, and they have shared some genes at a low level since then. Until 1996, Bornean and Sumatran orangutans were thought to be subspecies, but they were later classified as separate species after scientists studied their mitochondrial DNA. Tapanuli orangutans were recognized as a distinct species in 2017.

The Bornean orangutan has three subspecies:
• Northwest Bornean orangutan (Pongo pygmaeus pygmaeus) – found in Sarawak (Malaysia) and northern West Kalimantan (Indonesia).
• Central Bornean orangutan (P. p. wurmbii) – found in southern West Kalimantan and Central Kalimantan (Indonesia).
• Northeast Bornean orangutan (P. p. morio) – found in East Kalimantan (Indonesia) and Sabah (Malaysia).

Some scientists believe the group currently called P. p. wurmbii may be more closely related to Sumatran orangutans (P. abelii) than to Bornean orangutans. If this is true, P. abelii would be a subspecies of P. wurmbii. Additionally, the original location of P. pygmaeus is not certain. It may be from the population now called P. wurmbii, which could mean P. wurmbii is a later name for P. pygmaeus. Some researchers, like Bradon-Jones and others, think P. morio is the same as P. pygmaeus, and the population in East Kalimantan and Sabah might be a different, unnamed group.

In early October 2014, scientists from different countries discovered about 50 orangutans in several groups in South Kalimantan Province. This area had no previous records of orangutans.

As members of the Hominidae family, Bornean orangutans are one of the closest living relatives to humans (Homo sapiens).

This species was first discovered by native Malaysians. Orangutans appear in their folklore. However, the species was officially named and described by zoologist Carl Linnaeus in 1799. Its original name was Simia satyrus, meaning "satyr monkey." Later, scientists realized orangutans are not all one species, so the name was changed. The original specimen of this species is stored in the British Museum in London.

The genus name Pongo comes from the Bantu word "mpongo," which refers to a large primate. This name was originally used for chimpanzees in West African languages. The species name "pygmaeus" comes from the Greek word "pygmy," meaning "dwarf."

Description

The Bornean orangutan is the third-largest ape after the western gorilla and the largest ape that lives mainly in trees. Their body weights are similar to humans, even though humans are taller, and humans vary more in size. The Sumatran orangutan is about the same size but is slightly lighter on average. A study of wild orangutans found that male Bornean orangutans weigh about 75 kg (165 lb), with weights ranging from 50 to 100 kg (110 to 220 lb), and are 1.2–1.7 m (3 ft 11 in – 5 ft 7 in) long. Female Bornean orangutans weigh about 38.5 kg (85 lb), with weights ranging from 30 to 50 kg (66 to 110 lb), and are 1–1.2 m (3 ft 3 in – 3 ft 11 in) long. In captivity, orangutans can become very overweight, sometimes weighing more than 165 kg (364 lb). The heaviest known male orangutan in captivity was a male named "Andy," who weighed 204 kg (450 lb) in 1959 when he was 13 years old.

The Bornean orangutan has a unique body shape with very long arms that can measure up to 1.5 meters. It has grey skin, a coarse, shaggy, reddish coat, and grasping hands and feet. Its coat does not cover its face, unlike most mammals, but it has some hair on its face, including a beard and mustache. It also has large, fatty cheek pads called flanges and a hanging throat sac.

Bornean orangutans show strong differences between males and females. Males have much larger cheek pads, or flanges, made of muscle and fat, while females have flanges mostly made of muscle. Males also have larger canines and premolars, a more noticeable beard and mustache, and a larger throat sac. Among sexually mature males, there are two body types: smaller or larger. Larger males are more dominant, but smaller males can still breed successfully. At birth, there is little difference in size between male and female orangutans.

Distribution and habitat

The Bornean orangutan lives in tropical rain forests in the lowlands of Borneo and in mountainous rain forests up to 1,500 meters (4,900 feet) high. This species lives in the tops of both old and new forests and travels long distances to find trees with fruit.

It is found in two Malaysian states, Sabah and Sarawak, and four of the five Indonesian provinces in Kalimantan. Because of habitat loss, the orangutan’s range is now scattered across the island. The species is rare in the southeast part of Borneo and in the forests between the Rajang River in central Sarawak and the Padas River in western Sabah. Its presence in Brunei has not been confirmed.

The first complete skeleton of an orangutan was found in Hoa Binh province, Vietnam, and is believed to be from the late Pleistocene epoch. This ancient orangutan was similar to modern ones but had a smaller body compared to its head. These fossils show that orangutans once lived in mainland Southeast Asia, even though today they are only found in Malaysia and Indonesia.

Behavior and ecology

In history, orangutans lived in Southeast Asia, southern China, the island of Java, and southern Sumatra. They mainly live in peat swamp forests, tropical heath forests, and mixed dipterocarp forests. Bornean orangutans are more solitary than Sumatran orangutans. Two or three orangutans with overlapping territories may meet briefly, but they do not stay together long. Although orangutans are not territorial, adult males may show threatening behavior when meeting other males. They only socialize with females to mate. Males are the most solitary of all orangutans. Bornean orangutans live about 35–45 years in the wild and can live up to about 60 years in captivity.

Despite being tree-dwelling, Bornean orangutans travel on the ground more than Sumatran orangutans. This may be because there are no large predators in Borneo that threaten orangutans. In Sumatra, orangutans must avoid Sumatran tigers, which are dangerous predators.

Bornean orangutans build nests for sleeping or resting during the day. Young orangutans learn nest-building by watching their mothers. Juvenile orangutans practice this skill. Nests can be complex, with a foundation and mattress made from intertwined leaves and branches. Additional features, such as shade, waterproof roofs, "pillows," and "blankets" made from branches and leaves, may also be added. Nest-building in primates is considered an example of tool use, not animal architecture.

Bornean orangutans use tools such as leaves to clean themselves, a pad of leaves to hold spiny durian fruit, a leafy branch to swat bees, a bundle of branches as an "umbrella" during rain, a stick to scratch their backs, and a branch or tree trunk as a weapon.

The Bornean orangutan diet includes over 400 types of food, such as wild figs, durians, leaves, seeds, bird eggs, flowers, sap, vines, honey, fungi, spider webs, insects, and bark. They also eat the inner shoots of plants and vines. They get water from fruit and tree holes. Some orangutans have been seen eating dead fish on shore or catching live fish with their hands.

In some areas, orangutans eat soil to obtain minerals that help neutralize toxins and acids in their mostly plant-based diets. Rarely, they may hunt small primates, such as slow lorises.

Males and females usually meet only to mate. Subadult males try to mate with any female and are successful about half the time. Dominant males with flanges (a feature on their faces) call to attract females, who prefer to mate with them. Adult males often target females with weaned infants because these females are more likely to be fertile.

Females reach sexual maturity and have their first ovulatory cycle between 6 and 11 years of age. Those with more body fat may mature earlier. The estrous cycle lasts 22–30 days. Menopause has been observed in captive orangutans around age 48. Females typically give birth at 14–15 years old. Newborns nurse every 3–4 hours and begin eating soft food from their mothers’ lips at 4 months. During the first year, young orangutans cling to their mothers’ bodies by wrapping their fingers and gripping their hair. Offspring are weaned at about 4 years, though this may take longer. After weaning, they begin exploring but stay close to their mothers. They also play and travel with other young orangutans. On average, juveniles become independent around 7 years old. The birth rate of orangutans has decreased mainly due to habitat loss, which limits their access to nutrients.

A 2011 study on female orangutans in rehabilitation programs found that those given extra food had shorter time gaps between births and gave birth at a younger age.

Conservation status

The Bornean orangutan is more common than the Sumatran orangutan. There are about 104,700 Bornean orangutans living in the wild, while fewer than 14,000 Sumatran orangutans remain in the wild. Orangutans are becoming more endangered because of habitat loss and the bushmeat trade. Young orangutans are often captured and sold as pets, which usually results in the death of their mothers.

The Bornean orangutan is listed as critically endangered on the IUCN Red List of mammals and is protected under Appendix I of CITES. Scientists estimate that the total number of Bornean orangutans is less than 14% of what it was in the recent past, from around 10,000 years ago until the middle of the 20th century. This sharp decline has happened mostly in the past few decades due to human activities and development. Bornean orangutans are now found in small, scattered areas across Borneo. They are rarely seen in the southeast of the island and in the forest between the Rajang River in central Sarawak and the Padas River in western Sabah, including the Sultanate of Brunei. A population of about 6,900 orangutans lives in Sabangau National Park, but this area is at risk.

The United Nations Environment Programme supports this view. In a 2007 report, it stated that illegal logging, fires, and the expansion of palm oil plantations have caused orangutans to become critically endangered. If current trends continue, orangutans may become extinct. When forests are burned to make room for palm oil plantations, orangutans lose their homes. Some are burned or killed in these fires. Palm oil is used in many products, including packaged foods, deodorants, shampoos, soaps, candies, and baked goods. It accounts for more than one-tenth of Indonesia’s export earnings.

Climate change is another threat to Bornean orangutans. Human activities have changed rainfall patterns in Indonesia, making food less available. This makes it harder for orangutans to get enough nutrients to stay healthy and reproduce.

A survey in 2011, based on interviews with 6,983 people in 687 villages in Kalimantan between 2008 and 2009, found that between 750 and 1,800 orangutans were killed in the year before April 2008. These numbers were higher than previously believed, showing that orangutans in Kalimantan are in serious danger. The survey did not include numbers related to habitat loss from deforestation and palm oil plantations. It also found that 73% of people interviewed knew that orangutans are protected by Indonesian law.

However, the Indonesian government rarely punishes people who harm orangutans. In a rare case in 2011, two men were arrested for killing at least 20 orangutans and several long-nosed proboscis monkeys. They were ordered to do this by a supervisor at a palm oil plantation to protect the crop. The supervisor paid $100 for each dead orangutan and $22 for each monkey.

Several rescue and rehabilitation projects help orangutans in Borneo. The Borneo Orangutan Survival Foundation (BOS), founded by Willie Smits, operates rescue and rehabilitation centers in East Kalimantan (Wanariset and Samboja Lestari) and Central Kalimantan (Nyaru Menteng), which is managed by Lone Drøscher Nielsen. BOS also works to protect and restore orangutan habitats at Samboja Lestari and Mawas.

Orangutan Foundation International, started by Birutė Galdikas, rescues and rehabilitates orangutans to prepare them for release into protected rainforests. It also works to preserve rainforests for orangutans.

The Sepilok Orangutan Rehabilitation Centre, near Sandakan in Malaysian Borneo, opened in 1964 and was the first official orangutan rehabilitation project.

The Orangutan Foundation, founded by Ashley Leiman, operates in Central Kalimantan, Indonesia. It rescues orphaned orangutans and helps them develop survival skills through a soft-release program. When ready, orangutans are released into the Lamandau Wildlife Reserve. The foundation focuses on protecting habitats and helping local communities.

A study published in 2011 examined whether the lifespan of zoo-housed orangutans was linked to their well-being. Researchers studied 100 Sumatran orangutans, 54 Bornean orangutans, and 30 hybrid orangutans. Zoo staff used a questionnaire to assess the well-being of the orangutans. The study found that orangutans with higher well-being were less likely to die during the study period. It concluded that happiness was connected to longer lifespans in orangutans.

In late 2014, a female orangutan was not saved by veterinarians at Nyaru Menteng. During an operation, 40 air-rifle pellets were removed from her body. She was found at a palm oil plantation in Indonesian Borneo.

Genome and demographic history

Orangutans and humans separated into different groups about 14 to 18 million years ago. Around 17,000 years ago, Bornean orangutans moved to Sumatra, swapping places with the Sumatran orangutans that were already there. These two species have remained closely related throughout their history because they lived near each other. As a result, their genetic makeup and population history are similar. Scientists estimate the two species split about 3.5 million years ago. Even though they are now separate species, their genetic similarity is likely due to male orangutans from each group often moving between islands and mating with females from the other group. Because of this connection, researchers often study Bornean and Sumatran orangutans together, and many genetic discoveries relate to their shared history. Additionally, Bornean orangutans have less genetic diversity in their DNA compared to Sumatran orangutans. This is because Bornean orangutans have a smaller population.

Bornean and Sumatran orangutans belong to the same genus, so they share similar cultural behaviors found in most orangutan groups. These shared traditions likely occur because they live in similar environments and learn from each other early in life.

The Bornean orangutan has experienced a major split from its relatives and ancestors. During the Middle Pleistocene, there was little genetic exchange between the two species, as shown by studies of their Y-chromosomes. One reason for this may be the Sunda Shelf, where Borneo is located. During the Late Pleistocene, a dry climate increased genetic exchange between the two species. This led to early differences in their gene pools. Going back to the Middle Pleistocene, the Bornean orangutan population declined sharply, likely because they became isolated from their ancestors. Natural geographic barriers probably caused this isolation, allowing Bornean orangutans to move to new areas. This isolation also suggests that Bornean orangutans did not face a severe genetic bottleneck. Studies show that Bornean orangutans adapted physically to survive changes in their island’s climate.