Animal Info - Orang-utan

(Other Names: 紅毛猩猩, オランウータンBorneo Orang-utan, Maias, Orang-outan, Orang-után, Orangotango, Sumatran Orang-utan)

Pongo abelii and Pongo  pygmaeus

Status: P. abelii - Critically Endangered; P. pygmaeus - Endangered


Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (Taxonomy, IUCN Status, Countries Where Currently Found, Population Estimates, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Rate, Early Development, Dispersal, Maximum Reproductive Age, Maximum Age, Diet, Behavior, Social Organization, Mortality and Survival, Density and Range, Minimum Viable Population)
5. References


Profile

Pictures: Sumatran Orang-utan (6 Kb JPEG) (Kids Ecol. Corps); Young Orang-utan (13 Kb JPEG) (San Diego Zoo); Borneo Female Orang-utan and Young (23 Kb JPEG) (Gekoski-Kimmel/OFI)

Orang-utans have brown and rust-colored shaggy fur. They weigh an average of 50 kg (110 lb) and can weigh over 90 kg (200 lb). The orang-utan lives in tropical, swamp and mountain forests, where it eats mostly fruit, leaves and insects. The orang-utan is arboreal and diurnal. It exhibits a sophisticated use of tools for gathering food. Twigs and branches are utilized to construct a large nest-platform in a tree to sleep in at night.

Adult orang-utans are generally solitary, except when a male and a female are together for mating. The home range of an adult male usually overlaps the ranges of several adult females. Orang-utans are not territorial. Most animals in a given area appear to maintain a loose relationship, although adult males are hostile to one another. A single young is usually born about every six years.

The orang-utan was once found throughout Indo-China, Malaysia and north to China. In historical times it has only been known from Sumatra and Borneo. About 100 years ago it was present in most of the rainforest areas on these islands; however, it was never found in large numbers. It has declined drastically since then. The major causes of the orang-utan's decline have been 1.) in the past, capture for the pet and zoo trade, especially the capture of young, which usually involved killing the mother; and 2.) habitat loss, especially through permanent conversion to oil-palm plantations and for logging.


Tidbits

*** In the Malay language, "orang-utan" means "man of the forest."

*** "These animals are rare..." (Myers 1870).

*** Captive orang-utans score very highly in comparative intelligence experiments, which is somewhat surprising in view of their relatively simple life-style and social relationships (Macdonald 1984).

*** "The tool use we have observed among orang-utans rivals in sophistication the behavior of chimps. One female orang-utan used 54 tools for hunting insects and 20 tools for getting fruit. Each tool is custom-made for a particular task." (van Schaik & Dopyera 1997)


Status and Trends

Taxonomy:

Two species of Pongo are now differentiated: P. abelii ("Sumatran Orang-utan") and P. pygmaeus ("Orang-utan" or "Borneo Orang-utan") (Anon. 2001)

IUCN Status:

Countries Where the Orang-utan Is Currently Found:

2004 (Pongo abelii): Occurs in Indonesia (Sumatra).  (IUCN 2004)

2004 (Pongo pygmaeus): Occurs in Borneo (Indonesia (Kalimantan) and Malaysia (Sarawak)); may occur in Brunei. (IUCN 2004)

Population Estimates:

[Note: Figures given are for wild populations only.]

History of Distribution:

The orang-utan was once found throughout Indo-China, Malaysia and north to China, and possibly in India (e.g. the Siwalik Hills). In the past it was thought that the orang-utan had also occurred in Africa: "These animals are rare and inhabit the impenetrable forests of Borneo, Java and Sumatra, as well as those of Guinea and Congo..." (Myers 1870).

In historical times it has only been known to occur on Sumatra (Indonesia) and Borneo. About 100 years ago it was present in most of the rainforest areas on these islands; however, it was never found in large numbers. Although no population estimates are available prior to 1959, it is apparent from the earlier literature that it declined drastically during the century prior to the 1970's, especially after the departure of the Dutch from Indonesia and of the British from Singapore after World War II, whereupon the regulations and enforcement against commercial trade in orang-utans ceased to operate (Schuhmacher 1967). For example, its distribution in Sumatra declined 20-30% from the 1930's to the 1980's, and the species is now found only in the northern part of that island.  The Sumatran orang-utan is thought to have declined by more than 50% in the eight years prior to 2000 (IUCN 2003a, IUCN 2004).

Distribution Map (29 Kb JPEG) (iEARN Austral.)

Threats and Reasons for Decline:

The major threats have been 1.) in the past, capture for the pet and zoo trade, especially the capture of young, which usually involved killing the mother; and 2.) habitat loss, especially through permanent conversion to plantations and for logging.

In selectively-logged areas, orang-utan densities decrease on average by 60 % of prelogging levels.  Continued logging effectively eliminates orang-utans in the secondary forest left after timber depletion.  In one such area, orang-utan density fell by approximately 90 % within a year after selective logging followed by continued timber poaching.  (van Schaik et al. 2001)  

"The major threats to the survival of Sumatran orang-utans are identified as habitat loss (mainly from conversion to oil palm plantations), habitat degradation and habitat fragmentation. The immediate causes of this are identified as weak compliance with regulations and laws; weak law enforcement and the weak legal environment. Corruption is identified as the ultimate causal factor underlying these three immediate causal factors, along with a frontier mentality and bureaucratic constraints." (Yarrow Robertson & van Schaik 2001) 


Data on Biology and Ecology

Size and Weight:

A female orang-utan weighs 30 - 50 kg (66 - 110 lb) and grows to about 1.1 m (3.5') in height; a male weighs 50 - 90 kg (110 - 200 lb) and stands 1.2 - 1.5 m (4 - 5') tall.

Habitat:

The orang-utan is found in tropical, swamp and mountain forests.  

In Sumatra, orang-utans are largely lowland animals, being rare above 1000 m (3300') and virtually absent above 1500 m (4900').  The availability of fruit containing soft pulp (rather than dry or fibrous fruits) appears to be a major factor in their abundance patterns.  Altitudinal limits are even lower in Borneo where the mountain ranges also tend to be lower and thus vegetation zones are more altitudinally compressed.  (van Schaik et al. 2001)  

The orang-utan is one of the species that live in the Sundaland Biodiversity Hotspot (Cons. Intl. 2005) as well as the Northern Borneo-Palawan Moist Forests, Mt. Kinabalu Montane & Alpine Scrub & Forest, Sumatran-Nicobar Islands Lowland Forests, and Central Borneo Montane Forests Global 200 Ecoregions. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)

Age to Maturity:

Females reach puberty at 10 years of age, but do not give birth until they are 15.  Males usually become sexually mature at about 12 years. However, the time it takes for a male to attain full maturity, including the secondary sexual characteristics such as a facial "disk" formed from fibrous cheek flanges, a big throat pouch, and long hair on their arms and back, can range from 10 years to more than 20. (Macdonald 2001) 

Gestation Period:

233 - 265 days.

Birth Rate:

  • Usually only one young is born at a time. Occasionally twins are born.
  • Time between births is generally 7 - 9 years, (average 8).
  • A female orang-utan can produce at most four surviving young over a lifetime (Macdonald 2001).

Early Development:

Young orang-utans are usually weaned by the time they are about 3 years old and are carried by the mother when they travel until they are 4 years old (Macdonald 2001).

A young orang-utan is ready to fend for itself after 6 - 7 years (Speart 1992).

Dispersal:

Young females generally remain in the vicinity of their birth, but males emigrate to other areas (Nowak 1999).

Orang-utans are very poor dispersers in non-forest habitat, shunning these areas except in extreme discomfort (van Schaik et al. 2001) 

Maximum Reproductive Age:

About 30 years (male and female).

Maximum Age:

Estimates range up to 45 years in the wild and 59 years in captivity.

Diet:

About 60% of the orang-utan's diet consists of fruit, including durians, jackfruit, lychees, mangosteens, mangoes and figs. The remainder of the diet is mostly young leaves and shoots, but also included are insects, mineral-rich soil, tree bark and woody lianas and occasionally eggs and small vertebrates. Much of their water is obtained from the fruit in their diet, but it is also drunk from tree holes. (Macdonald 1984, 2001)

Behavior:

The orang-utan is arboreal and diurnal, with peaks of activity in the morning and late afternoon. It exhibits a sophisticated use of tools for gathering fruit and insects for food. An orang-utan utilizes twigs and branches to construct a large nest-platform in a tree that it sleeps in at night. It usually makes a new nest each night but sometimes reuses one.

Social Organization:

Although temporary groupings are sometimes formed, adults are generally solitary, except when a male and a female are together for mating. Home ranges of males overlap the ranges of several adult females. Most animals in a given area appear to maintain a loose relationship, although adult males are hostile to one another, apparently even after they are no longer sexually active.  Orang-utans are not territorial  (van Schaik et al. 2001).

Mortality and Survival:

Proportion of young that survive to age 1: approximately 0.91 (Dobson & Lyles 1989)

Density and Range:

Density:

  • In Sabah, densities ranged from 0.5 - 2 individuals/sq km (1.3 - 5 individuals/sq mi) (Davies 1986)
  • In Sabah, most orang-utans occurred at densities of 1.2 - 3.0 individuals/sq km (3.1 - 7.8 individuals/sq mi) whether or not the forests had been logged for commercial timber (Andau et al. 1994).
  • The "highest orang-utan density ever observed": 7 - 10 individuals/sq km (18 - 26 individuals/sq mi) (Gunung Leuser National Park, northern Sumatra) (van Schaik & Dopyera 1997)
  • Leuser Ecosystem, Northern Sumatra: prime habitat (fertile coastal swamps/alluvial floodplains and fertile uplands with soils unusually low in acidity): mean density = 3.5 indiv/sq km  (9.1 individuals/sq mi) (up to more than 7 or more indiv/sq km (18 individuals/sq mi)); good habitat (e.g. river valleys): mean density = 1.5 indiv/sq km (3.9  individuals/sq mi); marginal habitat: mean density = 0.75 indiv/sq km (2.0 individuals/sq mi) (van Schaik et al. 2001) 

Home range:

  • In Borneo, adult females, usually with dependent young, occupied overlapping home ranges of 0.65 sq km (0.25 sq mi) or less; adult males were generally alone and used home ranges of 2 - 6 sq km (0.8 - 2.3 sq mi). In Sumatra, both males and females lived in home ranges that overlapped considerably and were 2 - 10 sq km (0.8 - 3.8 sq mi) in extent. (Nowak 1999)

Minimum Viable Population:

Minimum viable population density: 0.10/sq km (0.26/sq mi) (Silva & Downing 1994).


References

Andau et al. 1994, Anon. 2001, Arkive, Aveling & Mitchell 1982, AZA 1998d, Borner 1976, Boyle 1963, Burton & Pearson 1987, Cons. Intl. 2005 Curry-Lindahl 1972, Davies 1986, Dobson & Lyles 1989, Fox 2002, iEARN Austral., IUCN 1966, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2004, Ivereigh 2003, Karesh 1997, Kids Ecol. Corps, Macdonald 1984, Macdonald 2001, Medway 1976, Myers 1870, Nowak 1999, Nowak & Paradiso 1983, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Oryx 1963b, Oryx 1977g, San Diego Zoo, Schaller 1961, Schuhmacher 1967, Silva & Downing 1994, Speart 1992, van Schaik & Dopyera 1997, van Schaik et al. 2001, Wildl. Cons. 2005, Yarrow Robertson & van Schaik 2001, ZooNet 1997


Top of Page | Search This Site

Home | Rarest Mammals | Species Index | Species Groups Index | Country Index | Links


Last modified: March 3, 2006;

© 1999 - 2014 Animal Info. Endangered animals of the world. SJ Contact Us.