The Koala (Phascolarctos cinereus) is an arboreal (tree-dwelling) herbivorous animal native to Australia, feeding almost exclusively on the leaves of the Eucalyptus tree, and the only known member of the family Phascolarctidae. This animal sleeps about 18 hours a day so it is rarely awake at all. Although sometimes referred to as a koala bear, it is not a bear at all, but rather a marsupial, which means it raises its young in a pouch on its belly.
The koala is found all along the eastern coast of Australia from near Adelaide to the southern part of Cape York Peninsula, and as far from the coast as there is enough rainfall to support suitable forests. The koalas of South Australia were largely exterminated during the early part of the 20th century, but the state has since been repopulated with Victorian stock. The koala is not found in Tasmania or Western Australia.
The pouch of the koala, unlike those of kangaroos and possums, but like those of wombats and the extinct Tasmanian tiger, faces to the rear, i.e., downward. And as the mother is unable to lick the pouch clean in readiness for a new fetus, as the kangaroo does, it has a remarkable self-cleaning mechanism.
The koala feeds almost exclusively on the leaves of selected species of the eucalyptus (Australian gum) tree. Its diet affects many of its characteristics.
The eucalyptus is unpalatable to other animals because of its high phenol and terpene content. The Koala's digestive system is especially designed or adapted to detoxify the poisonous chemicals in the leaves.
Besides being poisonous, Eucalyptus leaves are also fibrous and low in nutrition. To deal with this, koalas possess a very slow metabolic rate which allows them to keep food in their digestive system longer, thus maximising the amount of energy they can extract from it. At the same time, their slow metabolic rate reduces their energy requirements. Koalas will sleep for up to 18 hours per day in order to conserve energy.