Dean M. Chriss
Koala #2, Great Otway National Park, Victoria, Australia
(Click image to enlarge)
The koala (Phascolarctos cinereus) is a marsupial herbivore native to Australia and the only representative of the family Phascolarctidae still in existence. Koalas are found in coastal regions of eastern and southern Australia, and inland in regions with enough moisture to support suitable woodlands. Koalas are not found in Tasmania or Western Australia. Contrary to the popular name "koala bear", they are not bears.
These typically sleepy and slow moving animals can leap more than six feet to nearby tree branches and live almost entirely on eucalypt leaves. Although koalas obtain most of their water from the leaves, they will sometimes drink water from streams. They sleep as much as 18 hours a day due to their low-energy diet. When temperatures rise above approximately 26 ºC (80 ºF), koalas increase the evaporative cooling in their airways by increasing their respiration rates. They simultaneously compensate for the extra water loss by decreasing the amount of water in their urine. Unlike bears, koalas do not have an insulating layer of fat below their skin. In colder temperatures koalas will curl their bodies into a ball when sleeping to reduce heat loss. At temperatures below about 10 ºC (50 ºF) koalas will sometimes shiver to produce extra body heat.