Behaviour

The amount of time orangutans spend in different activities varies greatly, depending on a range of external and internal factors such as food availability, social behaviour and age. As the graph below illustrates, orangutans spend a significant amount of their time either feeding or resting.  Daily activity shows two peaks; after leaving the nest in the morning, orangutans spend 2-3 hours foraging and feeding, before resting for several hours, often building a 'day nest' in which to rest.  They spend another couple of hours foraging and feeding in the afternoon. Sleeping night nests are built anywhere between mid afternoon and early evening. Within a typical day, an adult's range may vary between 90 metres and more than three kilometres, with males generally travelling further.

The two species of orangutan display differing amounts of their time in the trees and on the ground. Sumatran orangutans tend to stay off the forest floor more, due to the presence of tigers. However, both species spend a great deal of their time up in the forest canopy, where they use both their hands and feet (with opposable thumbs and 'big' toes, respectively) to hold on to and manipulate branches as they move through the forest. When on the ground, orangutans walk quadrupedally, using their fists to bear weight. In contrast, African great apes knuckle-walk. On occasions, orangutans are seen walking bipedally and there is much debate as to whether human bipedalism originated in the ancestral anthropoid ape common to both orangutans and humans, rather than in early humans.

One aspect of behaviour which sets orangutans apart from all other monkeys and apes is their semi-solitary social behaviour. Bornean orangutans are not being strictly solitary and display social behaviour in terms of mother-young groupings, occasional male-female pair bonds after copulation and feeding aggregations around certain tree-fruiting events. Females and males are estimated to spend 25% and 9% (respectively) of their time in the company of other orangutans. The Bornean orangutan is less social than its Sumatran counterpart; probably due to greater competition and less availability of simultaneous fruiting and fig trees.

In terms of territory and ranges, young males do often band together, travelling in small parties, which break up before adulthood. An adult female typically occupies a home range along with her infant and any dependant juveniles and these ranges overlap with those of other adult females, which may be mothers, aunts or sisters. Several of these female home ranges fall within the area of an adult male territory, where he attempts to exercise exclusive breeding rights with the receptive females. However, other males often enter these territories in search of females. Bornean orangutans practice a behaviour known as 'philopatry', whereby they remain within the groups or home ranges in which they were born, while males leave at sexual maturity.  These small groups of related females in their overlapping home ranges attract unrelated males, avoiding the problems associated with inbreeding. Although often related, adult females can be aggressive to one another when they meet, or can coexist in a non-aggressive manner.  Males encountering each other usually display some form of agonistic behaviour, such as attack or threatening behaviour or conversely, retreat or appeasement. After leaving their mother, male Bornean orangutans pass through a nomadic phase, where they travel often long distances until they find a suitable territory, where they typically secure a territory through the displacement of the resident male. This displacement occurs as aggressive vocalisations, visual display and even fighting.

Photographs kindly provided by David Slater, Nick Bramley, STA

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Bornean orangutan (Pongo pygmaeus) orang-utan - ape facts behaviour - Borneo Sabah South East Asia - Wildlife Holiday Responsible Travel