45.
Sumatran Orangutan
(Pongo abelii)
CR
Overview
Orangutans are the only great apes to occur outside of Africa, and are the largest arboreal mammals in the world. They are extremely intelligent, and have shown evidence of tool use and culture - traits once believed to be uniquely human. Despite being one of our closest relatives, human activities are having a devastating impact on the Sumatran orangutan and its habitat. This species is the slowest breeding of all mammals, giving birth to a single young every 8 years. With such a low reproductive rate even a small decrease in numbers can lead to extinction. Concerted conservation efforts are needed to prevent this peaceful primate from being first great ape to become extinct in the wild.
Urgent Conservation Actions
Included expanding the moratorium on logging concessions, improving patrols and law enforcement, stopping illegal logging, promoting forest restoration, halting road construction and addressing human-orangutan conflict.
Distribution
Sumatra, Indonesia
Associated Blog Posts
5th Apr 12
  On the 26th of March 2012, a huge fire raged across the Tripa peat swamp forests in Aceh, Indonesia, started by the company PT Kallista Alam to...  Read

Media from ARKive
ARKive image - Sumatran orangutan infant
ARKive video - Sumatran orangutan overview
ARKive video - Juvenile Sumatran orangutans playing
ARKive image - Sumatran orangutan infant held by mother
ARKive video - Infant Sumatran orangutans interacting with mothers
ARKive image - Sumatran orangutan female with infant
ARKive video - Female Sumatran orangutan suckling young
ARKive image - Sumatran orangutan female nursing infant
ARKive video - Sumatran orangutans feeding on leaves
ARKive image - Sumatran orangutan with infant
ARKive image - Sumatran orangutan female with older infant
ARKive video - Sumatran orangutans stripping bark from tree
ARKive image - Sumatran orangutan infant hanging upside down from tree
ARKive video - Group of Sumatran orangutans feeding on fruit
ARKive image - Sumatran orangutan infant helped by mother
ARKive video - Mother & juvenile Sumatran orangutans drink water from a hole in a tree
ARKive video - Sumatran orangutan eating the roots of a fern
ARKive image - Young Sumatran orangutan licking sap from tree
ARKive image - Sumatran orangutan and young catching rain
ARKive video - Sumatran orangutans eating ants from tree
Evolutionary Distinctiveness
Order: Primates
Family: Hominidae
The family Hominidae comprises seven living species in four genera: Homo (humans), Gorilla (gorillas), Pan (chimpanzees) and Pongo (orangutans). Apes are thought to have diverged from Old World monkeys between 22 and 30 million years ago (mya). They were confined to Africa until around 15-17 mya, when they colonised Eurasia across a newly formed land bridge between the two continents. Here they underwent rapid dispersal and diversification, with the evolution of many new species including the ancestors of modern orangutans. This Eurasian ape radiation also includes the extinct genus Sivapithecus (formerly known as Ramapithecus), which was once thought to be one of the earliest human ancestors. Out of all the great apes, orangutans are the least closely related to humans, having split off from the early hominid lineage 10 to 12 million years ago. Gorillas were the next lineage to diverge, followed finally by the chimpanzee-bonobo lineage.

The orangutan is the only Great Ape in Asia and has recently been re-classified as comprising two distinct species, (reflecting their geographical distribution): Pongo pygmaeus (on Borneo) and Pongo abelii (on Sumatra). Genetic studies have identified the Sumatran orangutan as the more ancient lineage.
Description
Size: 
Head and body length: Up to 1.4 m (male)
Weight: 100 kg (males)
Orangutans are the largest arboreal mammal in the world. They have a coarse, shaggy reddish-brown coat, which covers most of their body with the exception of the hands, soles of their feet and part of the face. The colour varies from bright orange in young animals to maroon or dark brown in some adults. Skin colour also varies, from pink in youngsters to almost black in some adults. Their long, powerful arms can reach up to 2 m in length. Both the thumbs and the large toes are opposable, allowing the apes to grasp branches with both its hands and feet.

The orangutan is highly sexually dimorphic, with males growing to about twice the size of females. When sexually mature, males develop flanges on either side of their faces, known as ‘cheek pads’. These are deposits of subcutaneous fat bound by connective tissue. Adult males also develop throat sacs, which can be inflated to add resonance to the male’s loud ‘long-call’.

The two species of orangutan differ slightly in appearance and behaviour. Sumatran orangutans are generally thinner, have a paler red coat and have longer fur around their faces than the Bornean species. They also have narrower faces and cheek pads.
Ecology
Orangutans eat, sleep and travel in the trees. They are active during the day, and spend the majority of their time searching for and consuming food. Fruit such as figs, durians, jackfruit, lychees, mangosteens and mangos are eaten when available, along with smaller quantities of leaves, seeds, ants, termites and bark. Individuals tend to switch to eating these lower quality foods when fruit is scarce, rather than move to another area. In some areas over 400 different types of food have been recorded as part of the species’ diet. At night, individuals sleep in a nest made of twigs or leaves high up in the trees. They generally make a new nest each night, although old nests are occasionally re-used.

Unlike other diurnal primates – which are social and gregarious – orangutans lead a semi-solitary lifestyle. This is thought to be primarily due to the scattered distribution of their food. There is generally not enough fruit in an area at any one time to support a large group of orang-utans. Adult males occupy large, overlapping home ranges, which encompass those of several females. They spend almost all of their time alone, coming together with females only to mate. Although males are not territorial, they are generally hostile to one another. Confrontations are rare, as the male’s long-call is thought to serve to repel rivals, as well as advertise his availability to sexually receptive females. Female orangutans are slightly more social than the males. They maintain small, overlapping home ranges, and occasionally come together to feed when food is plentiful. In general, juvenile males and females display the most social behaviour, and are often observed feeding, playing and travelling together in groups. Social behaviour in Sumatran orangutans tends to coincide with the simultaneous (or “mast”) fruiting of fig trees, which does not occur in Borneo. The fact that Sumatran orangutans have more opportunity to come together to eat fruit that the Bornean species has enabled greater sociality among individuals. This in turn has enabled them to learn tool-using behaviour from one another. Orangutans play an important role in their forest habitat; they act as seed dispersers and help to open up the forest canopy which allows light to reach the forest floor so that the forest can regenerate.

The orangutan is the slowest breeding of all primates. Females reach sexual maturity at around 12-15 years of age, and generally give birth to a single young every 8-9 years thereafter, depending on the quality of the habitat. Infants are totally dependent on their mothers, and are carried constantly for the first two to three years of their lives. Weaning occurs at around 3.5 years, but the infant will remain close to its mother for at least another three years, learning the spatial and temporal patterns of fruiting in the forest. When the young disperse, females usually set up a home range adjacent to their mothers, while males tend to travel further afield. Life expectancy in the wild is thought to be more than 50 years. The incredibly long inter-birth period – the longest of any land-based mammal – means that a female orangutan can produce a maximum of four surviving young during her lifetime.
Habitat
Inhabits lowland tropical rainforests and swamps up to 800 meters above sea level.
Distribution
Fossil evidence indicates that orangutans once ranged throughout south-east Asia as far north as China. Today, they are only found in pockets of forests on the islands of Borneo and Sumatra. The Sumatran orangutan is restricted to remaining patches of rainforest in northern Sumatra, Indonesia. Most remaining populations occur in and around Gunung Leuser National Park near Aceh, a protected area around 10,950 km² in area.
Population Estimate
There are believed to be around 6,600 individuals surviving in just ten fragmented habitat units.
Population Trend
Decreasing. The population is believed to have declined by more than 80% in the last 75 years.
Status
Classified as Critically Endangered (CR A2cd) on the 2010 IUCN Red List of Threatened Species.
Threats
The Sumatran orangutan is listed as one of the top 25 most endangered primates. The greatest threats to species are habitat loss and fragmentation resulting from logging, conversion of forest to agricultural land and oil palm plantations, and road construction. Habitat supporting around 1,000 orangutans was being lost each year in the Gunung Leuser Ecosystem alone during the late 1990s. This was largely due to legal logging concessions and conversion of lowland forests to palm oil estates, but illegal logging and encroachment was also taking place in some areas.

The rate of habitat loss decreased markedly in many areas during the Aceh civil conflict, as activities in the forests became unsafe, and as a result of a moratorium imposed on logging in the province by the Aceh government. However, a peace deal negotiated in 2005 led to political stability and many new applications to open up logging concessions and palm oil estates in orangutan habitat. Of major concern is the re-issuing of logging permits for large tracts of forest in Aceh and the controversial Ladia Galaska road project in the Leuser Ecosystem, which is poised to fragment two of the three largest remaining orangutan populations. The increased access provided by the road is also likely to result in illegal encroachment and logging, and poaching of threatened species.

Throughout their range orangutans are sometimes killed as pests along forest edges as they raid agricultural crops, and in the far south of their range they are occasionally still hunted as food. The pet trade, which was booming from 1900 to the 1960s, with a further surge in the 1980s, resulted in the death of up to 30,000 orang-utans. For every young orangutan that ends up in captivity there is a loss of about 50 from the wild population, due to the number that are directly killed before and the loss of a potential breeding animals. A small but significant pet trade in young Sumatran orangutans still persists.
Conservation Underway
Since 1975 orangutans have been listed under Appendix I of CITES, which affords them the highest degree of protection against international trade. They are also legally protected from hunting throughout their range. However, these regulations are difficult to enforce. By far the most significant populations, totalling some 5,600 animals, are found within the Leuser Ecosystem, a 26,000 km² conservation area that encompasses the smaller Gunung Leuser National Park (10,950 km²) and the 1,025 km² Singkil Swamps Wildlife Reserve. The Ecosystem and the national park within it form the only conservation area of note where viable wild populations of the Sumatran orangutan exist. However, the mountainous terrain of the National Park is not ideal habitat for the predominantly lowland orang-utan, and the majority are found outside the park boundaries.

Orangutans found in logging areas are often transported to sanctuaries created by the Indonesian government while orphaned youngsters may be “rehabilitated” for release at rehabilitation centres. However, these measures can only save a small number of animals and overcrowding and inbreeding in the relatively small, isolated reserves are likely.
Conservation Proposed
Recommended conservation actions include: effective law enforcement and prosecution to stop hunting of orangutans for food and trade; mitigation of human-orangutan conflict in agricultural areas, including large-scale plantations; audits to assess the compliance of forestry concessions to their legal obligation to ensure orangutans are not hunted in concession areas; increased environmental awareness at a local level; and mechanisms for monitoring orangutan populations and forest cover.
Links
References
Mittermeier, R. A. et al. 2006. Primates in Peril: The World’s 25 Most Endangered Primates, 2004–2006. Primate Conservation (20): 1–28.

Singleton, I., Wich, S.A. & Griffiths, M. 2008. Pongo abelii. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on 05 November 2009.

Wich, S. A. et al. 2008. Review: Distribution and conservation status of the orang-utan (Pongo spp.) on Borneo and Sumatra: how many remain? Oryx, 42(3), 329–339.

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