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BiologyBornean orang-utans are predominantly solitary, occupying large overlapping home ranges. The largest arboreal mammal, they spend almost all of their time in the trees, clambering between branches or using their body weight to bend and sway trees (2). Each night a nest is built from bent branches, high up in the trees (5). Orang-utans are the slowest breeding of all mammal species, with an inter-birth interval of approximately eight years (7). They are long-lived and females tend to only give birth after they reach 15 years of age. The infant spends its first two to three years being carried constantly and will still remain close to the mother for at least another three years (7). The orang-utan diet is composed of over 400 types of food, including wild figs (Ficus spp.) and durians (Durio spp.) (7). When fruit is scarce however, orang-utans will feed on leaves, seeds and even bark (5).