Bornean orangutans (Pongo pygmaeus) are currently found on the Southeast Asian island of Borneo and generally inhabits swampy and hilly tropical rainforests. Bornean orangutans have a patchy distribution throughout the island and is completely absent from the southeast region. Fossil evidence suggests that Bornean orangutans were once widespread throughout Southeast Asia and evenly distributed across the entire island of Borneo. Due to illegal logging and the destruction and conversion of tropical forest to agricultural land this once expansive range has decreased dramatically. ("Great Apes and Other Primates", 2011; Ancrenaz, et al., 2008; Lang, 2010; Schulz, et al., 2011)
Bornean orangutans are arboreal and rarely descend to the ground. They generally live in the old growth forests ranging from the lowland swampy areas to the dipterocarp forests. The peat swamps and flood-prone dipterocarp forests produce more fruit than the dry dipertocarp forests and have a higher density of Bornean orangutans because they migrate depending on fruit availability. Bornean orangutans inhabit the primary tropical rainforest and secondary forest at lower elevations and are rarely seen above elevations of 1000 meters. (Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010; Pamungkas and Marshall, 2005)
Bornean orangutans have orange-red hair and long arms, which are advantageous for traveling through the canopy. Bornean orangutans grasp with both their feet and hands, which suites their arboreal life. Both sexes have throat pouches for calling but the male’s throat pouches are larger than the females. Bornean orangutans are sexually dimorphic, with males having an average height and weight of 970 mm and 87 kg respectively, and females averaging 780 mm and 37 kg, respectively. Males also develop large cheek pads known as flanges and develop a sagittal crest where large temporal muscles attach. ("Great Apes and Other Primates", 2011; Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010)
Bornean orangutans exhibit bimaturism, or two different forms of mature males. These two types of males are denoted as being either flanged and unflanged. Flanged males are twice the size of females, have a large facial disk with flanges, and a large throat patch. Unflanged males look much more like the females as they are the same size and do not display the same calling behavior as flanged males. Both types of adult male orangutans reproduce in the population. Unflanged males may become flanged at any time, as it is a reflection of social hierarchy as well as age. Males between 8 and 15 years of age are generally unflanged and become flanged between 15 and 20. (Ancrenaz, et al., 2008; Lang, 2010)
Bornean orangutans are distinguishable from their Sumatran cousins in their morphology. After diverging 1.5 million years ago, Bornean orangutans have become heavier and thicker, have darker red coats, long course hair, and the males have larger flanges covered in bristly hair and larger throat pouches. (Ancrenaz, et al., 2008; Lang, 2010)
Dominant flanged males often have an established territory that will encompass multiple females' territories. The multiple females within the male’s territory will copulate with him and produce his offspring. Younger unflanged males often cannot sustain a home range of their own and are forced to wander throughout the forests. When these small, wandering males come into contact with a female, the small unflanged male will force copulation. This is different from the flanged males which will long-call; a call to help receptive females locate him. Females prefer to mate with flanged males, which may be a way to ensure protection from unflanged males. (Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010)
Bornean orangutans do not have a breeding season, but females show higher ovarian function during periods of food abundance. Ovulation in Bornean orangutans occurs on the 15th day of a 30-day cycle. Copulation generally occurs with both parties hanging with their arms and facing each other. Bornean orangutan's gestation period lasts about nine months after which they give birth to a single infant, although twins have been recorded. Research shows that female orangutans only breed every 6 to 8 years, and the young are nursed until age 6 and remain at the mother's side until the next birth. The offspring has contact with its mother after birth, but once female offspring start to display sexual behaviors, they begin traveling separately. Once the female offspring is separated from its mother completely, it will move off and establish a territory nearby its mother’s territory. Adolescence in Bornean orangutans starts at 5 years of age and lasts until around 8 years of age. Male offspring remain socially immature despite being sexually mature. The young males avoid contact with mature males and start to wander the forests until they become a flanged male and establish their own resident territory. Female Bornean orangutans will reach menopause around the age of 48 years. (Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010)
Female Bornean orangutans invest a lot of time in their offspring, taking care of them until they reach adolescence at around 6 years of age. Since Bornean orangutans are semi-solitary in nature, the males have very little contact and no investment in their young. From birth, the offspring will be in constant contact with the mother for 4 months and will be carried everywhere the mother goes. The offspring remains completely dependent upon the mother for the first 2 years of life. At about 5 years of age, the offspring will begin to make short trips on its own, usually staying within sight of the mother. The orangutan young may start to build its own nests as play, and will eventually start sleeping in the nests it builds. The offspring are usually weaned by 4 years of age and will begin adolescence soon after. The offspring will generally stay around the mother until the next offspring are born. After this, the young females establish their own territory and the young males travel the forest until they can establish their own home territory. ("Great Apes and Other Primates", 2011; Ancrenaz, et al., 2008; Lang, 2010)
Bornean orangutans are long lived like many of the other great ape species. They often live more than 50 years in the wild and have been documented to live up to 59 years in captivity. ("AnAge entry for Pongo pygmaeus", 2009; Lang, 2010)
Bornean orangutans are diurnal and rarely come down from the trees. Small groups of females may travel with their infants in search of food, but adult males are usually solitary. While all Bornean orangutans are generally solitary they may have occasional social connections. Groups of 6 or more Bornean orangutans are rare but can be found during times of mast fruiting; when a group of trees suddenly fruit at the same time. Daily and seasonal movements change frequently and are influenced by the availability of fruit. Bornean orangutans use multiple methods of locomotion. Brachiation is only seen in young orangutans whereas older orangutans walk quadrupedally, or occasionally bipedally. When walking quadrupedally, they walk on their fists rather than their knuckles, unlike other great apes. Bornean orangutans sleep in nest platforms made of vegetation 40 to 60 feet off the ground. Food is plucked with the fingers and the palm due to their inability to use their thumbs. Bornean orangutans cannot swim which make rivers and other water sources impassable boundaries, limiting their range. ("Great Apes and Other Primates", 2011; Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010; Pamungkas and Marshall, 2005; Schulz, et al., 2011)
Adult male Bornean orangutans can have home ranges from 2 to 6 sq km and will often incorporate multiple female home ranges. When a young female is establishing her home range, she will often choose a range nearby or bordering her mother's range. (Ancrenaz, et al., 2008; Lang, 2010)
Bornean orangutans are not as social as other species of great apes and do not have as many social vocalizations. The most prominent form of communication for Bornean orangutans is the long-call, a one to two minute call performed only by flanged males. The long-call can be heard from several kilometers away in the right conditions. The main purposes of long-calls are to inform other males of the caller's presence (when unflanged males hear long-calls they flee the area) and to call out to sexually responsive females. Long-calls are spontaneous and do not follow any specific pattern. Some evidence suggests that the long-call can even suppress the development of unflanged males. When the unflanged males hear a long-call, stress hormones are produced which inhibit the development of the unflanged males. The other type of calling produced by Bornean orangutans is a fast-call, which is most often made after male-to-male conflict. In addition to the long and fast calls, Bornean orangutans smack their lips to produce sounds when in small social groups. When scared, Bornean orangutans will funnel their lips and scream. (Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010)
Bornean orangutans are frugivorous, and spend two to three hours in the morning feeding avidly. Their diet consists of forest fruits, leaves and shoots, insects, sap, vines, spider webs, bird eggs, fungi, flowers, barks, and occasionally nutrient rich soils. Bornean orangutans have been documented eating more than 500 plant species as part of their diet. Fruits make up more than 60% of their total dietary intake and they will migrate depending on fruit availability. ("Great Apes and Other Primates", 2011; Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010; Pamungkas and Marshall, 2005)
The only predator of Bornean orangutans are humans. Even hunting for traditional purposes at a 2% hunting rate, is not sustainable for the current population of orangutans. Bornean orangutans are not subject to predation from large felines like their Sumatran cousins, although clouded leopards are able take down a young Bornean orangutan. (Ancrenaz, et al., 2008; Groves, 1971; Lang, 2010)
Since fruits make up more than 60% the Bornean orangutan diet, they play a vital role in seed dispersal, especially for the larger seeds which cannot be dispersed by smaller animals. Bornean orangutans play such a crucial role in seed dispersal that they have been given the title "gardeners of the forest". (Ancrenaz, et al., 2008)
The Bornean orangutans keep the forests healthy by dispersing seeds, and eco tourism for the Bornean orangutans draws in important revenue for orangutan conservation agencies. (Ancrenaz, et al., 2008; Lang, 2010)
Bornean orangutans have the highest density in areas where there is valuable timber such as the peat swamps. In the second half of the 19th century, the Bornean orangutans lost 80% of its viable habitat. These forests are also being illegally logged, as people are logging before the 30 to 40 year rest period is over. Palm oil tree saplings are eaten after logging occurs and the orangutans are searching for another food source. The Bornean orangutans also compete with humans for durian fruit and will on rare occasions attack humans. (Ancrenaz, et al., 2008; Groves, 1971)
Bornean orangutans are an endangered species. Since all Bornean orangutans are totally depenent on the trees for survival, forest degradation is devastating to the population. Even though the fruiting trees are not the coveted timber, the removal of trees from the area still negatively influences the overall quality of the forest. Because Bornean orangutans have to travel to find the fruiting trees, a patchy forest hinders travel and dispersal and increases competition for these limited resources. ("Pongo pygmaeus", 2012; Ancrenaz, et al., 2008; Lang, 2010)
If the Bornean orangutan is going to recover, habitat destruction must be stopped. These orangutans also need to be protected, and any harvesting for meat or for illegal pet trade must be stopped. Both of these current practices are not sustainable and may lead to the extinction of the Bornean orangutans. (Groves, 1971; Lang, 2010)
Benjamin Strobel (author), University of Wisconsin-Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, Alecia Stewart-Malone (editor), University of Wisconsin-Stevens Point, Laura Podzikowski (editor), Special Projects.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
animals that live only on an island or set of islands.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
having more than one female as a mate at one time
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
young are relatively well-developed when born
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