Orangutans are large, arboreal apes primarily found in the rainforests of Borneo and Sumatra in Southeast Asia. Their name, “person of the forest,” reflects their arboreal lives. These primates are largely herbivorous, with their diet closely linked to the diverse plant life within their habitat.
Primary Food Sources
Orangutans consume a wide variety of foods, with ripe fruits forming the largest portion of their diet, sometimes making up as much as 90% when abundant. They show a preference for fleshy, calorie-rich fruits such as durians, figs, and jackfruits. These fruits provide essential sugars and fats, supplying the energy needed for their large bodies and arboreal lifestyle.
Beyond fruits, orangutans incorporate other plant parts. Young leaves and shoots constitute a significant portion, around 25% of their diet, alongside flowers, buds, and even roots. They also consume bark, especially the nutrient-rich inner layer called cambium, which is a key food source when fruits are scarce.
Orangutans eat various insects, including termites, ants, bees, and caterpillars, which provide protein. Occasionally, they may also consume bird eggs or small vertebrates like slow lorises. Some orangutans even ingest soil, a practice known as geophagy, thought to help neutralize plant toxins and provide minerals.
Seasonal Variations and Foraging
The availability of food, particularly fruits, fluctuates seasonally in the rainforest. Orangutans adapt their diet to these changes, relying on “fallback foods” such as leaves, bark, and insects when fruits are less abundant. This dietary flexibility allows them to survive periods of scarcity.
Orangutans employ intelligent foraging strategies to locate food sources. They possess extensive knowledge of their forest environment, including the locations of fruiting trees and their seasonal cycles. Their memory helps them track changes in fruit availability. Orangutans typically spend up to six hours a day foraging, often moving slowly through the canopy as they search for food. While much of their water comes from succulent fruits, they also drink from leaves, tree hollows, or occasionally directly from streams.
Dietary Differences Across Species
While the diets of the three recognized orangutan species—Bornean (Pongo pygmaeus), Sumatran (Pongo abelii), and Tapanuli (Pongo tapanuliensis)—are broadly similar, subtle distinctions exist reflecting their specific habitats.
Sumatran orangutans, for instance, tend to be more consistently frugivorous due to more predictable fruit supplies in their environment. They also appear to consume more insects compared to their Bornean counterparts.
Bornean orangutans, inhabiting rainforests with more unpredictable fruiting seasons, show a greater reliance on bark and other fibrous vegetation as fallback foods. Their digestive systems are adapted to efficiently extract nutrients from these tougher plant materials.
The recently identified Tapanuli orangutan, found in a limited region of Sumatra, exhibits some unique dietary behaviors, including the consumption of unusual items like certain caterpillars and conifer cones.