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General descriptionOrang-utan is derived from a Malay term meaning "man of the forest". Sumatran orangutans are the largest non-human primates in Asia and the largest arboreal primates. In fact, orabgutans are the only primarily arboreal great apes, characterized by strong sexual dimorphism and delayed development of mature male features, a long life span and the longest interbirth interval among mammals.
DistributionSumatran orangutans inhabit the northern part of island of Sumatra, in Indonesia. They are found in primary tropical lowland forests, including mangrove, swamp forests, and riparian forests. They live almost completely in the trees, building nests in which they nap or sleep for the night.
Conservation statusPongo abelii is the rarer than Pongo pygmaeus (Bornean orangutan) that still occurs in many scattered parts of Borneo. In 2002, the World Conservation Union put the species on the IUCN Red List with critically endangered status. In 2004, population of Sumatran orangutans was estimated to be 7,000-7,500 individuals and 40,000-50,000 Bornean individuals remained in the wild in fragmented populations.
Orangutans' crossing in Washington DC zoo
Interbirth interval is about 9.3 years, the longest among primates (Wich et al., 2004).
- Embryo Average gestation period is about 251 days.
- Post natal
- Infant An infant is completely dependent upon its mother for 2-3 years; weaning typically occurs around 48 months of age. Available data indicate that infant mortallity in the first year of life is approx. 8%, which is far lower than rates for mountain gorilla (26%) or chimpanzee (20%). This high infant survival in the wild may be explained by the absence or rarity of infanticide in orangutans.
- Juvenile Offsprings are dependent on their mother until 8-9 years of age; once fully developed, a male will leave his mother to find his own territory; developed, independent young female will either disperse or take up residence near her mother's territory. Juvenile mortality (before 11 years of age) was 33% as observed for period of 6.9 years in Sumatra (Wich et al., 2004).
- Adult Age of attainment of sexual maturity and adult size varies from 15 to 24 years old for males and from 9 years to 15 years for females. There are two distinct morphs of adult males: one called flanged that is large-bodied and possesses secondary sexual characteristics (e.g., pronounced cheek flanges) and the other called unflanged that is smaller, lacks secondary sexual characteristics, but is still capable of reproduction. Female life spans range from 44 to 53 years in the wild; male life spans are slightly longer, 47 to 58 years. The Sumatran Orangutan grows to about 4.6 feet tall and 200 pounds in males. Females are smaller, averaging 3 feet and 100 pounds.
Similarities between orangutan and human
Orangutan is considered to be most primitive of all apes and is the least similar to humans in DNA sequence similarity. Nevertheless, humans share many unique features with orangutan. Just a few most interesting are enumerated below.
- a hairline recedes from the eyebrows
- forehead hair orient forward
- male has beard and mustache
- longest hair length
Reproductive biology and life history
- no swelling or color change in the genitalia during ovulation
- females may mount and provide pelvic thrusting after first manipulating the penis to produce an erection
- prolonged copulation with average of 9 or 15 minutes (copulation times in other apes: ~1.5 min in gorilla, ~7 sec in chimpamzee, 13-15 sec in bonobos)
- ventroventral mating represents the majority of orientations in human and orangutans
- unlike other apes orangutans prefer to mate in private
- copulation during pregnancy occurs in orangutans and humans
- female orangutans may form long-term pair bonds with the same male between child-rearing intervals
- orangutans have the slowest rate of maturation of all the great apes and perhaps longevity in the wild (at least 58 years fro males and approx. 53 years for females)
- in their interest and ability to solve mechanical problems orangutans are superior to all other apes
- orangutans and humans are the only primates habitually to construct shelters with roofs
- orangutans readily imitate familiar humans and orangutans
- aesthetics: adolescent and subadult male orangutans sometimes carry fresh branches or vines when approaching another individual, usually draping them around the head or neck
- capacity for closed-mouth smile, which produces dimpling of the cheek in humans and orangutans and is either absent or extremely rare in other primates
- orangutans have fuzzy sense of species boundaries: males have forcibly mated with human females and females made physical attempts on human males
- intellectual performance by chimpanzees and orangutans in various cognitive tests is among the highest of any primate; shared abilities include understanding of bartering, planning, mirror self-recognition, intentional deception, tool usage, etc.
Orangutans in Tampa zoo, Florida, April 2013
Ancrenaz M, Dabek L, O'Neil S. The costs of exclusion: recognizing a role for local communities in biodiversity conservation. PLoS Biol. 2007 Oct 23;5(11):e289.
Pongo pygmaeus in Borneo. At eight years old, orangutans like Etin, who lives in the KOCP intensive study site in the Lower Kinabatangan Sanctuary, start wandering alone in the forest to find a new territory. (Image: Jamil Sinyor)
Gross L. Genetic evidence that humans have pushed orangutans to the brink of extinction. PLoS Biol. 2006 Feb;4(2):e57. Epub 2006 Jan 24.
Ongoing deforestation and palm oil plantations leave no room for the orang-utan.
- Grehan JR. Mona Lisa smile: the morphological enigma of human and great ape evolution. Anat Rec B New Anat. 2006 Jul;289(4):139-57. (Free article)
- Beaudrot LH, Kahlenberg SM, Marshall AJ. Why male orangutans do not kill infants. Behav Ecol Sociobiol. 2009 Sep;63(11):1549-1562.
- Animal Diversity Web: Pongo abelii
- Wikipedia: Sumatran Orangutan
Cover images credit: http://kotomatrix.ru/