As nighttime approaches in a tropical rain forest in parts of Sumatra and Borneo in Asia, orangutans prepare for sleep. In forks of trees high off the ground, shaggy, red-haired apes bend branches down to form comfortable mattresses of leaves and twigs. They sometimes add a roof built from more branches, so that if it rains they will stay dry.

Equipped with very long, powerful arms and hook-shaped hands and feet, these apes climb and swing from tree to tree with ease. They reach from one tree to the next with their long arms, grasping the next branch with long hands or feet, and swing their bodies across the gap. If a baby following its mother reaches a gap between trees that is too wide for it to navigate, its mother makes a living bridge for the baby to scamper across. Sometimes heavier males can't find branches strong enough to hold their weight, so they climb down to get to the next suitable tree.

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On the ground, orangutans walk on all fours. Orangutans find their food in the trees where they live. More than half their diet consists of fruit. They also eat nuts, bark, and other parts of plants and trees. Every once in a while they eat insects such as ants and termites, as well as bird eggs.

Orangutans find the water they need for drinking up in the trees—in hollows, on leaves, or even on their own fur after a rain. Trees are essential to every aspect of the orangutans' world. The cutting down of trees—deforestation—has landed this species on the endangered species list.

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