An infant Sumatran orangutan in Gunung Leuser National Park, Indonesia

© Cyril Ruoso/Minden Pictures

An infant Sumatran orangutan in Gunung Leuser National Park, Indonesia

Orangutans are only found in the rainforests of Sumatra and Borneo, where they are known as the heaviest mammals to travel by tree. Infants, like the baby Sumatran orangutan shown here, travel with their mothers for several years before setting out on their own. All three species of orangutans are critically endangered and face many challenges, including habitat loss and the illegal wildlife trade. Non-profits like the World Wildlife Fund are working to protect habitat for orangutans and many other species in Southeast Asia.