Orangutans of the Rainforest


Describer (Date): Linnaeus, 1760 (Simia pygmaeus)

    Phylum: Chordata
        Class: Mammalia
             Order: Primates
                    Superfamily: Anthropoidea
                         Family: Hominidae (synonym: Pongidae)
                              Genus: Pongo
                                  Species: P. pgymaeus
                                        Subspecies: Pongo pygmaeus pygmaeus, Bornean Orangutan
                                                            Pongo pygmaeus abelii, Sumatran Orangutan

Taxonomy and Nomenclature

  • Some researchers believe that the Pongo is too different morphologically and behaviorally from humans to include it in Hominidae, and prefer to retain Pongidae.
  • Based on recent genetic data, many researchers believe that the subspecies of orangutan should be elevated to full species status; still controversial due to a high level of intra-island variation.
  • Common Names: Orangutan, Orang hutan, Mawas, Mawih, Kihau, Man of the Forest, Orange Ape


  • Of the great apes, orangutans are the least related to humans, splitting off from the common ancestral group the earliest (10 to 20 million years ago), followed by gorillas, and then finally by chimpanzees and bonobos.
  • Sivapithecus most probable ancestor, from late Miocene, Asia. Theory is controversial; many doubt the relationship due to differences in skeletal morphology between Pongo and Sivapithecus.
  • Recent discovery in northern Thailand of 130 million year old fossil teeth, very similar to the orangutan; adds to the confusion of orangutan evolution. Lufengpithecus chiangmuanensis could be a relative or ancestor (Chaimanee, et al.  2003)).
  • The two subspecies of orangutans diverged from one another 2.3 to 0.5 million years ago.


(Rijksen, and Meijaard, 1999)(Van Schtick et al., 1995)


  • Prehistoric distribution:
    • Originated on the Asian mainland approximately 2-3 million years ago.
    • Distribution spanned across mainland Asia from northern India, to southern China, Viet Nam, the Malay peninsula, Singapore, and Java.
  • Present range:
    • Sumatra and Borneo
    • The orangutan's range in Borneo is fragmented into at least 61 pieces, and in Sumatra into 23 pieces
    • The reduction in range of the orangutan during the Pleistocene was most likely due to selective hunting by prehistoric humans, and to changing environmental conditions.


  • Ideal habitat: alluvial forest, lowland swamps, and mountain foothills; up to 200-400 m in elevation; an abundance of fleshy fruits.
  • In Borneo orangutans are not found above 100 m; in Sumatra some populations can be found at 12,000-12,500 m.
  • Usually found within 100-150 km of water (stream, river, swamp)
  • Seasonal changes in abundance of orangutans due to heterogeneous distribution of fruit


(Delgado and van Natugnaro, 2000)(Grooves, 1971)

Body Weight:
males, 45-100 kg (99-220 lbs); females, 35-50 kg (77-110 lbs)
Body Length:
(average):males, 956 mm (37 in.); females, 776 mm (30 in.)
Standing Height:
(average): males, 1366 mm (54 in.); females, 1149 mm (45 in.)


  • Skin dark gray
  • Arms about twice as long as trunk
  • Legs are short, a little more than half the length of the arms
  • Cheek teeth bunodont (low, rounded)


  • Long, flowing, reddish pelage
  • Face of males and females sparsely covered, but may have beard and moustache.

Sexual Dimorphism

  • Very large cheek pads in males
  • Hanging throat sac present in both sexes, but much larger in males
  • Males are larger and heavier than females
  • Males have larger canines and first lower premolars
  • Males have more pronounced beard and moustache

Sub-specific Differences: May be due to individual rather than sub specific differences

  • Bornean orangutans (P. p. pygmaeus)
    • male facial flanges curved forward
    • male gular (throat) sacs larger and pendulous
    • darker color of hair and face
    • hair shorter and less dense
  • Sumatran orangutans (P.p. abelii)
    • male facial flanges lie flat
    • male gular (throat) sac smaller
    • lighter color of hair and face
    • hair longer, thicker, more wooly

(Rijksen, 1978)(Smith, et al., 1995)

  • Confiscated orangutans in Indonesia have high incidence of disease including tuberculosis, hepatitis A, B, C, and E, cholera, and malaria. Parasites also common.
  • Rehabilitant orangutans in Sumatra were found to have myiasis (fly maggots) infestations, leeches, intestinal parasites (helminth larvae, nematodes, hookworm), ticks, chiggers, scabies; also upper respiratory diseases such as the cold, sniffles, and flu.
  • Data on disease and pathology in the wild is limited.

(Bigchins, et al., 2001)(Rijksen, 2001)

Population Status

  • Bornean orangutan population declined from 23,000 to 15,400 between 1995 and 1998; approximately 7% of the estimated population from 1900.
  • Sumatran orangutan population in 2000 estimated at 12,500 individuals; approximately 14% of the estimated population from 1900.
  • It is estimated that orangutan populations have declined as much as 50% since 1990.
  • The present orangutan population in the wild is 14,000-25,000.
  • In 2002 the Nature Conservancy surveyed remote areas of Borneo and found evidence of approximately 1,000-1250 orangutans, previously unknown, representing up to 10% of the current orangutan population.
  • ISIS captive population (link requires Internet Explorer)
  • Conservation

    • CITES: Appendix I
    • IUCN: Vulnerable
    • In Indonesia: Protected
    • Rehabilitation centers have been set up to acclimate once-captive orangutans to life in the wild.
    • Problems with reintroductions: behavioral problems due to previous association with humans; high incidence of disease.

     Threats to survival

    • Habitat loss and fragmentation: logging, clearing for cash crops, human population pressure, fires, drought
    • Hunting by humans for the pet trade, sport, and for food
    • Political unrest, making it difficult to implement conservation strategies
    • Extremely slow reproductive rate makes the orangutan more vulnerable to long-term disturbance
    • Orangutans' highly arboreal lifestyle makes them more vulnerable to habitat fragmentation, as they rarely travel long distances on the ground.