Background Information
Orangutans are the world's largest tree-dwelling mammals. The name means "man of the forest" (8). It is the only primate species to experience bimaturism in males and the only non-human ape still inhabiting Asia (3 & 4). Recent reviews of the subspecies have found the Bornean (Pongo pygmaeus) and Sumatran (Pongo abelii) to be two distinct species rather than sub-species (5). This reflects their geographical distribution (4 & 6). The two species display both behavioural and physical differences, sumatrans are more frugivorous, and have narrower cheek pads (4). Not only do the Bornean orangutans tend to be smaller in size and darker in colour but they are also divided into several further distinct geographic types (3).
Exact numbers are unknown but significantly decreasing. Most recent population estimates are shown below:
Conservation Status :
Social status: Orangutans have the longest juvenile/mother dependency of any animal, and will often nurse until they are 6 or 7 years of age. They are semi-solitary individuals (3), however individuals will maintain complex social networks of loose relationships (6). Males tend to leave when they reach puberty while females will stay with their mothers for longer. They will only come together for a few days during when females are receptive to mating or when food in abundant (3). Orangutans are very intelligent animals, and will regularly use tools for varying purposes, for example to using leaves as an umbrella during excessive rain periods. Each night they make a nest high up in the trees using leaves and branches (3). Tool use, however has mostly been observed in the Sumatran species (4). |
Average height standing up:
Average weight:
Average lifespan:
Offspring:
(3) |
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The orangutan has a similar digestive tract to that of the Gorilla, they both contain a large intestine with high volume and length. This reflects their ability to ferment large amounts of fibre and metabolise energy (11). Orangutan diets contain large amounts of non-starch polysaccharides, which require microbial fermentation in order to be metabolised as energy. The gastrointestinal tract of these animals is formed by a simple stomach, a relatively long small intestine and a complex haustrated caecum and colon. It is believed that digesta retention and fermentation of non-starch polysaccharides occurs in the proximal colon (12).
Like many aspects of exotic animal nutrition, the degree of fibre fermentation in orangutans is not known. They are classed as frugivores however the chemical composition of their diet and their gastrointestinal anatomy suggests that they depend heavily on the fermentation of fibre for a substantial portion of energy (13). |
Wild Diet
Orangutan diet consists primarily of fruit, shoots, seeds, leaves, bark, insects (10), nuts and honey. Their diet composition varies monthly as they are strong opportunistic foragers (15). The Sumatran oraguntan eats more fruits and insects than the Bornean (14). Fruits can account for over 60% of their diet (6), this dietary preference is believed to be responsible for their solitary status as availability is seasonal and cannot accommodate large groups (10). They will consume less energy dense foods during these periods, some experts believe that they use energy reserves that had been previously stored as fat during high availability periods (11). Data from other studies also suggest that orangutans efficiently use stored fat from fruit-rich periods during times of shortage (16). During these scarce periods, orangutans will spend the majority of their time foraging for shoots and leaves. They have also been observed eating soil, and on rare occasions small vertebrates (14) and have been known to feed on more than 500 species of plant (6).
Foraging differs between sexes (15) but they spend an average of 4.3-6.3 hours per day performing this task and often show bimodal patterns of foraging (14) in various habitats (15). Most of their water requirements are met through the consumption of vegetation (14). |
Captive Diet
Captive orangutans receive significantly different diets than they would in the wild. This has lead to health problems, like cardiovascular disease, obesity, undesirable behaviours and metabolic abnormalities. In captivity, orangutans receive diets consisting mainly of commercially manufactured feeds/biscuits and fruits which have a much higher calorific value than in the wild. Due to the lack of dietary information most zoos follow recommendations established by the National Research Council found in the Nutrient Requirements of Nonhuman Primates (2003) manual. The wide range of foods eaten in the wild creates difficulties in assessing its nutritional composition and what time of the year they should be provided (17). |