Youngsters also get yogurt. The fruits they consume often have much more fiber and less water and sugar than fruit substitutes found in zoos. In Southeast Asia, they consume leaves, buds, young twigs of trees, fruits, seeds and nuts, as well as some insects, occasional bird eggs and small animals. With a bigger hindgut, they can harbor more bacteria to break down the plant cell walls for energy. Two main problems with zoo animals include obesity and diabetes.
Orangutans typically eat fruits and leaves in nature, and very little animal matter.
Some of the zoo problems may be associated with diets that are too easily digested, along with not enough exercise or activity in obtaining foods. The aye-aye is a very primitive primate from Madagascar. It has a very long middle finger, which it uses to tap on trees to find insects, then to dig them out for dinner. But last year I had the opportunity to work with a woman who studied their feeding habits for her doctoral thesis. During the two years she watched, they ate nuts of a certain tree, large grubs, small grubs, and a dry fungus.