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Conservation situation

With exponentially increasing habitat degradation, fragmentation, and transformation, orangutans are facing a number of threats (Kinnaird and O’brien, 1998; van Schaik et al., 2001; Meijaard et al., 2005; UNEP, 2007; Yuwono et al., 2007).

The timber industry and palm oil plantation development are the main driving forces behind the destruction of the forests. Between 1950-2000, 40% of Indonesia’s forests were cleared, reducing ground cover from roughly 162 million hectares to 98 million (FWI/GFW, 2002). Focusing on oil palm alone, of the 6.5 million hectares of land covered by plantations in 2006, 4.58 and 1.26 million were located in Sumatra and Kalimantan, respectively (EOA, 2007).

Although orangutans exhibit high behavioural and dietary flexibility that allows them to persist in secondary logged forest (Lackman-Ancrenaz et al., 2001), densities do decline following logging, particularly in the long term (reviewed in Rijksen and Meijaard, 1999; Meijaard et al., 2005). All current wild populations have already been deemed to be at their carrying capacity (Singleton and Aprianto, 2001). The Sumatran orangutan population has decreased by 86% over the past 100 years (van Schaik et al., 2001).

The most recent estimate places the figure around 7,300 left in the wild, with steady losses occurring every year (van Schaik et al., 2001; UNEP, 2007). Thus the Sumatran orangutan is now classified as critically endangered (Cr A2bcd) and is also listed as one of the twenty-five most endangered primates in the world (IUCN, 2006). The Bornean orangutan, with a greater remaining habitat range, is at less risk of immediate extinction and classified as Endangered (EN A2cd) (IUCN, 2006).

These two islands represent the last remaining habitat for orangutans. Forest cover in Sumatra was reduced by 61% from 1985-1997 due to logging, infrastructure development, internal migration, and plantation development (McConkey 2005), with the Sumatran orangutan population showing a decrease of 86% over the past 100 years (Robertson & van Schaik, 2001).

The most recent estimate places the figure around 6,624 left in the wild, with steady losses occurring every year (Wich et al., 2008). Thus the Sumatran orangutan is now classified as critically endangered (Cr A2bcd) and is also listed as one of the twenty-five most endangered primates in the world (IUCN, 2006). The Bornean orangutan, with a greater remaining habitat range and a population estimate of at least 54,000, is at less risk of immediate extinction but still classified as Endangered (EN A2cd) (IUCN, 2006; Wich et al., 2008).

Orangutans as a flagship species

Orangutans are highly charismatic species, and draw a great deal of attention to the rainforests of Sumatra and Borneo. They are what is referred to as an ‘umbrella species’. An umbrella species is one whose home range and habitat requirements are large enough that when it is protected, many of the species in that home range are also automatically protected.

The orangutan, with its predominantly arboreal (tree-dwelling) existence and generalized frugivory, equate to no other species being able to match it in functional representation of the rainforest (Rijksen & Meijaard, 1999). If there is an orangutan population at normal density, the area is likely to host at least five other primate species, at least five hornbill species (Family Bucerotidae), at least 50 different fruit tree species, and 15 different lianas (Rijksen & Meijaard, 1999).

A shortlist of species which share the Sumatran orangutans’ rainforest habitat:

  • Gibbons and siamangs (Family Hylobatidae)
  • Thomas leaf monkeys (Presbytis thomasi)
  • Long tailed macaques (Macaca fascicularis)
  • Pig tailed macaques (M. nemestrina)
  • Greater slow lorises (Nycticebus coucang)
  • Elephants (Elephas maximus sumatrensis)
  • Rhinoceros (Dicerorhinus sumatrensis)
  • Tigers (Panthera tigris sumatrae)
  • Sunbears (Helarctos melayanus)
  • Wild boars (Sus scrofa)
  • Rhinoceros hornbills (Buceros rhinoceros)
  • Various remarkable species of flora, such as the parasitic titan arum (Amorphophallus titanium), and the world’s largest individual flower, Rafflesia arnoldi

Laws concerning orangutan protection

In Indonesia, orangutans are legally protected. According to UU No. 5 (1990), any person who is found guilty of the poaching, killing, or trading (including for the pet trade) of orangutans can be sentenced to a maximum of five years imprisonment and/or a maximum of an $11,000 (£5,500) fine. Orangutans are further protected by Indonesian law under The Law of Wild Life Protection No. 233 /1931, UU No. 5 (1990), SK Menhut 10 Juni (1991) No. 301/Kpts-II (1991) and PP No. 7 (1999).

International legislation such as the Convention on International Trade in Endangered Species (CITES), prohibits the unlawful movement of orangutans between countries.

Orangutan distribution

Orangutans are restricted to the southeast Asian islands of Borneo (which is split between the Indonesian territory of Kalimantan and the Malayan territory of Sabah) and Sumatra, with over ninety per cent living in the territory of Indonesia, the world’s fourth most populous nation (Fig. 1.1). The Sumatran orangutan (Pongo abelii) is now recognized as a separate species from the Bornean orangutan (P. pygmaeus) (Zhang et al. 2001).

Sumatran orangutan distribution is currently restricted to 18 separated habitat blocks, ranging in size from 10km2 to 934km2, with the most viable populations being in the 2.5 million hectare Leuser Ecosystem (which includes the 1 million hectare Gunung Leuser National Park) (Wich et al. 2008). These ecosystems allow for orangutan densities of 3 to 6 individuals per square kilometer to occur with home ranges 5 to 25km2 or larger for males and 1 to 10 km2 for females (Rijksen & Meijaard 1999). Although the Leuser Ecosystem is an officially recognized conservation area it consists almost entirely of government forest land, approximately one third of which can be legally logged or transformed for agricultural use (van Schaik et al. 2001).

Orangutan life history

Female orangutans have the longest interbirth interval of any primate, with a mean duration of eight years (Galdikas and Wood, 1990). The mother-infant bond is very strong in orangutans, with offspring remaining dependent for up to six years (Rodman, 1988). Both species of orangutans are reported to survive up to forty-five years of age (and potentially past fifty) (Leighton et al., 1995; Singleton, 2004, cited in McConkey, 2005), with females not giving birth until approximately fifteen years of age (Galdikas, 1981). This equates to four to five surviving offspring per mother – perhaps the lowest reproductive potential of any mammal (van Schaik, 2001).

Orangutan sociality

Wild populations of orangutans consist of solitary adult males, lone adult females usually accompanied by one or two dependent offspring, and independent subadults or adolescents (Galdikas, 1981; Rodman, 1988). Adult males form a home range which encompasses a series of smaller overlapping adult female home ranges. There is a marked level of aggression between adult males and these home ranges are actively patrolled and defended against other adult males 1998; Utami et al. 1997). Females tend to stay near the range they were born, whereas males disperse and form a home range two to three times the size of females (McConkey, 2005).

Orangutans have this semi-solitary nature due to dietary constraints inherent in the Southeast Asian rainforests (Delgado & van Schaik 2000). This is the main factor as animals that are better fed have more time and energy for sociality (van Schaik, 2001). Sociality in orangutans can thus perhaps best be described as “neighborhoods, where residents know many others, but know them less well as the home range overlap decreases” (van Schaik, 2001, p.30).

Adult male orangutan long calls

The adult male alone emits a powerful, bellowing vocalization termed the “long call” which is audible to humans up to 800m away (Galdikas 1981; Schuermann 1982). The function of long calls is disputed. Some posit it may serve as a mechanism to announce one’s presence to females and intimidate other males (Delgado & van Schaik 2000; Maggioncalda et al. 1999). Others believe the long call to only be important to other males and claim it has minimal intersexual function (Mitani 1985). It could also be that adult male long calls serve as socioendocrine signals that serve in deferring subadult male development (Dixson 1998; Graham 1988; Graham & Nadler 1990; Maggioncalda et al. 1999).

Male bimaturism

There is a pattern of bimaturism observed in males (Utami Atmoko & van Hooff 2004): (1) the fully developed male with secondary sexual characteristics – large cheek flanges, enlarged laryngeal sac, beard, and growing to approximately twice the size of an adult female; and (2) the arrested subadult whom is fully fertile yet retains the characteristics of an adolescent male – slightly larger than a female but otherwise undeveloped. The proximate mechanism by which subadult male orangutans develop secondary sexual characteristics is yet unknown (Delgado & van Schaik 2000; Graham & Nadler 1990)!.


Due to such levels of habitat transformation, an increasing number of orangutans are being displaced from the forest (Eudey, 1995; Rijksen, 1995; Wolfe and Fuentes, 2007). With the opening up of the forest, orangutans are often captured and sold into the pet trade. However it is illegal in Indonesia (Undang-Undang No 5 Tahun 1990) to obtain and keep orangutans (WWF, 2005), so upon discovery they are confiscated by the authorities and taken into reintroduction programs.

Rehabilitation and reintroduction (henceforth referred to as ‘reintroduction’) of orangutans began in the 1960s when it was thought that the orangutan was nearly extinct in the wild, with an estimated number of 5,000 (Harrison, 1962, cited in Singleton and Aprianto, 2001). It is intended for the purposes of fighting the illegal pet trade as well as to reinforce the free ranging populations living in the wild (Rijksen and Meijaard, 1999). .

Fast Facts

Q: What do orangutans eat? Their main food is fruit (60%) Young leaves (25%) Flowers and bark (10%) Insects, mainly ants, termites and crickets (5%) And the occasional egg. In Sumatra they have been seen eating slow loris (Nycticebus coucang), but it is felt this is opportunistic feeding and not active hunting as is seen in chimpanzees (Pan troglodytes).

Q: Are orangutans nocturnal? No, they are active during daylight and go to bed at sunset – 7pm.

Q: How long can orangutans live? In the wild an average lifespan is 45-50 years. They have been known to live up to 60 years in captivity.

Q: How many babies are born at a time? Usually only one infant, very rarely are twins born, they are pregnant the same length of time as humans, nearly 9 months.

Q: When does the infant leave its mother? Orangutan infants stay with their mother until they are about 6 or 7 years old. They receive breast milk for the first three years of their life but also learn to eat other foods. The mother teaches them everything about survival in the forest. They have a very close relationship.

Q: Do they live in families? No, as adults they spend most of the time on their own. Babies and children stay together with their mother. However mothers and young orangutans do sometimes meet up and the infants play together (see above!).

Q: How old are orangutans before they reach maturity? Females can start having babies between 9 and 12 years old. Male orangutans start between the ages of 9 and 15 years. After that he will grow his beard, moustache then cheek pads grow. The cheek pads and throat pouch may not appear until he is older than 20 years and might not happen at all (see above!).

Q: Do orangutans have houses? They make or use old nests but only for short time stays during the day and overnight.

Q: Where do orangutans sleep? They sleep in their nests, usually a new one every evening. They are woven in a branch of a tree often very well made, like a big basket. Sometimes the nests can be more than a metre across. Orangutans also build nest in the daytime to rest and play in; a mother with young children might build 2 or 3 nests a day. A mother also uses a nest to give birth in.

Q: Are they dangerous or aggressive? Normally no, sometimes in captivity they can become aggressive as a result of how they are treated. They are up to 4 times stronger than humans and have 4 hands and can bite hard. Usually they are very peaceful animals. If an adult male meets another, they will try and avoid a fight by giving threat displays and staring at each other. If this does not work then they may fight.

Q: Do orangutans have any predators? Since the orangutan is the most arboreal (tree-living) ape, they are relatively safe from predation. However, there are a few – primarily man! The clouded leopard and the Sumatran tigers are also predators but with their decline in population this is not so much of an issue any longer.



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