The Bornean orangutan has a life span of 35-45 years in the wild; in captivity it can live to be about 60. A survey of wild orangutans found that males weigh on average 75 kilograms (170 lb), ranging from 50–100 kilograms (110–220 lb), and 1.2–1.4 metres (3.9–4.6 ft) long; females average 38.5 kilograms (85 lb), ranging from 30–50 kilograms (66–110 lb), and 1–1.2 metres (3.3–3.9 ft) long.
The Bornean orangutan is an endangered species, with deforestation, oil-palm plantations and killing posing a serious threat to its continued existence.
The Bornean orangutan and the Sumatran orangutan diverged about 400,000 years ago. There has been a continued low level of gene flow between them since then. The two orangutan species were considered merely subspecies until 1996, following sequencing of their mitochondrial DNA.
The Bornean orangutan has three subspecies:
- Northwest Bornean orangutan P. p. pygmaeus - Sarawak (Malaysia) & northern West Kalimantan (Indonesia)
- Central Bornean orangutan P. p. wurmbii - Southern West Kalimantan & Central Kalimantan (Indonesia)
- Northeast Bornean orangutan P. p. morio - East Kalimantan (Indonesia) & Sabah (Malaysia)
The Bornean orangutan has a distinctive body shape with very long arms that may reach up to two metres in length. It has a coarse, shaggy reddish coat and prehensile, grasping hands and feet.
Habitat and distribution
The Bornean orangutan lives in tropical and subtropical moist broadleaf forests in the Bornean lowlands as well as mountainous areas 1,500 metres (4,900 ft) above sea level. This species lives throughout the canopy of primary and secondary forests and moves large distances to find trees bearing fruit.
It can be found in the two Malaysian states of Sabah and Sarawak, and three of the four Indonesian Provinces of Kalimantan. Due to habitat destruction the species distribution is now highly patchy throughout the island, the species has become rare in the south-east of the island, as well as in the forests between the Rejang River in central Sarawak and the Padas River in western Sabah.
Behavior and ecology
In history, orangutans ranged throughout Southeast Asia and into southern China, as well as on the island of Java and in southern Sumatra. Orangutans primarily inhabit peat swamp forests, tropical health forests, and mixed dipterocarp forests.
The Bornean orangutan is more solitary than its Sumatran relatives. Two or three orangutans that have overlapping territories may interact, but only for short periods of time. Although orangutans are not territorial, adult males will display threatening behaviors upon meeting other males and only socializing with females to mate. Males are considered the most solitary of the orangutans.
Despite being arboreal, the Bornean orangutan travels on the ground more than its Sumatran counterpart. It is theorized this may be in part because there is no need to avoid the large predators which only exist in Sumatra such as the Sumatran tiger.
The Bornean orangutan diet is composed of over 400 types of food, including wild figs, durians, leaves, seeds, bird eggs, flowers, honey, insects, to a lesser extent than the Sumatran orangutan, and bark. They have also been known to consume the inner shoots of plants and vines. They get the necessary quantities of water from both fruit and from tree holes.
Bornean orangutans have been sighted using spears to catch fish. The species has been observed using tools such as leaves to wipe off feces, a pad of leaves for holding spiny durian fruit, a leafy branch for a bee swatter, a bunch of leafy branches held together as an "umbrella" while traveling in the rain, a single stick as backscratcher, and a branch or tree trunk as a missile." And in other regions, orangutans occasionally eat soil to get minerals that may neutralize the toxins and acids they consume in their primarily vegetarian diet. On rare occasions, orangutans will prey upon other, small primates such as slow lorises.
Males and females generally come together only to mate. Sub-adult males (unflanged) will try to mate with any female and will be successful around half the time. Dominant flanged males will call and advertise their position to receptive females, who prefer mating with flanged males. Adult males will often target females with weaned infants as mating partners because the female is likely to be fertile.
Females reach sexual maturity and experience their first ovulatory cycle between about 6 and 11 years of age, although females with more body fat may experience this at an earlier age. The estrous cycle lasts between 22 and 30 days and menopause has been reported in captive orangutans at about age 48. Females tend to give birth at about 14-15 years of age. Newborn orangutans nurse every three to four hours, and begin to take soft food from their mothers' lips by four months. During the first year of its life, the young clings to its mother's abdomen by entwining its fingers in and gripping her fur. Offspring are weaned at about four years but this could be much longer, and soon after they start their adolescent stage of exploring, but always within site of their mother. During this period they will also actively seek other young orangutans to play with and travel with.
A 2011 study on female orangutans in free-ranging rehabilitation programs found that individuals who were supplemented with food resources had shorter inter-birth intervals as well as a reduced age at first birth.
The Bornean orangutan is more common than the Sumatran, with about 54,500 individuals in the wild; there are only about 6,600 Sumatran orangutans left in the wild. Orangutans are becoming increasingly endangered due to habitat destruction and the bushmeat trade, and young orangutans are captured to be sold as pets, usually entailing the killing of their mothers.
The Bornean orangutan is endangered according to the IUCN Red List of mammals, and is listed on Appendix I of CITES. The total number of Bornean orangutans is estimated to be less than 14 percent of what it was in the recent past (from around 10,000 years ago until the middle of the twentieth century) and this sharp decline has occurred mostly over the past few decades due to human activities and development. Species distribution is now highly patchy throughout Borneo: it is apparently absent or uncommon in the south-east of the island, as well as in the forests between the Rejang River in central Sarawak and the Padas River in western Sabah (including the Sultanate of Brunei). There is a population of around 6,900 in Sabangau National Park, but this environment is at risk. According to an anthropologist at Harvard University, it is expected that in 10 to 20 years orangutans will be extinct in the wild if there is no serious effort to overcome the threats that they are facing.
This view is also supported by the United Nations Environment Programme, which stated in its 2007 report that due to illegal logging, fire and the extensive development of oil palm plantations, orangutans are endangered, and if the current trend continues, they will become extinct.
A November 2011 survey, based on interviews with 6,983 respondents in 687 villages across Kalimantan in 2008 to 2009, gave estimated orangutan killing rates of between 750 and 1800 in the year leading up to April 2008. These killing rates were higher than previously thought and confirm that, the continued existence of the orangutan in Kalimantan, is under serious threat. The survey did not quantify the additional threat to the species of habitat loss due to deforestation and expanding palm-oil plantations. The survey found that 73% of respondents knew that orangutans were protected by Indonesian law.
However the Indonesian government rarely prosecutes or punishes perpetrators. In a rare prosecution in November 2011, two men were arrested for killing at least 20 orangutans and a number of long-nosed proboscis monkeys. They were ordered to conduct the killings by the supervisor of a palm oil plantantion, to protect the crop, with a payment of $100 for a dead orangutan and $22 for a monkey.
Rescue and rehabilitation centers
A number of orangutan rescue and rehabilitation projects operate in Borneo.
The Borneo Orangutan Survival Foundation (BOS) founded by Dr Willie Smits has rescue and rehabilitation centres at Wanariset and Samboja Lestari in East Kalimantan and Nyaru Menteng, in Central Kalimantan founded and managed by Lone Drøscher Nielsen. BOS also works to conserve and recreate the fast disappearing rainforest habitat of the orangutan, at Samboja Lestari and Mawas.
Orangutan Foundation International, founded by Dr Birutė Galdikas, rescues and rehabilitates orangutans, preparing them for release back into protected areas of the Indonesian rain forest. In addition, OFI promotes the preservation of the rain forest for the orangutans.
The Sepilok Orangutan Rehabilitation Centre near Sandakan in the state of Sabah in Malaysian Borneo opened in 1964 as the first official orangutan rehabilitation project.