At night, females and youngsters sleep in a nest of branches placed in the fork of a tree. Because males are heavier, they generally prefer to sleep on the ground. At daybreak, orangutans leave their nests and go searching for food. Orangutans are far less sociable than other apes, and do not live in large social groups. Adult males are particularly solitary, and stake out areas of forest that they defend as their own territories, fighting other males who intrude, if necessary.
Females occasionally group together loosely with their young.
Fruits, nuts, leaves, bark, insects, and eggs form the diet of an orangutan. When the food supply in a particular area is plentiful, an orangutan may remain in one place for a period of time to feed. Orangutans, like the other apes, appear to be highly intelligent. The can memorize the geography of their surroundings and will travel great distances to find trees that have ripe fruit. When orangutans are thirsty, they locate a hollow in a tree where water has collected from past rainstorms.