Koala bear is often incorrectly used as the common name for Phascolarctos cinereus.  Phascolarctos cinereus is not a bear, and one of the main differentiating characteristics is that koalas are herbivores, whereas bears are carnivores (Sotzek 1997).  Even the giant panda, whose diet consists almost entirely of bamboo, is still considered a carnivore because of its carnivorous genes and digestive system (San Diego Zoo 2011). 

Koalas almost exclusively feed on the leaves from eucalyptus, a genus of flowering trees most commonly found in Australia (Lee 1988). Although there are more than 600 species of eucalyptus, koalas only eat 20 of these species, and actually prefer only a handful (PBS Nature 2013).  Koalas eat approximately two and a half pounds of leaves each day (Grosvenor 1998).  The eucalyptus leaves are low in protein, hard to digest, and toxic to most organisms (Encyclopedia of Life 2013).  A reasonable question is “why would the koala’s diet consist almost entirely of this innutritious plant?”  The benefit to eucalyptus leaves is that they provoke little competition.  However, the koala had to evolutionary adapt to consume these plants as the majority of their diet.  Koala stomachs contain bacteria that are able to metabolize the toxins that are present in the leaves (Encyclopedia of Life 2013).  They also have powerful jaws and enlarged hindguts, so the maximum amount of nutrients can be extracted from the eucalyptus leaves (Lee 1988).  In addition, koalas have very low metabolic rate and relatively small brains (Encyclopedia of Life 2013), and sleep up to twenty hours a day (Phillips 2006).  Thus, koalas don’t burn vast amounts of energy.  There is also some evidence that suggests koalas vomit their partially digested food and then re-chew it.  This process, termed myrecism, would result in greater energy being extracted from the eucalyptus leaves (Encyclopedia of Life 2013).

To the Aborigines, the native people of Australia, koala means “no drink” (Sotzek 1997).  Koalas drink very little water, and get most of the water they need from the eucalyptus leaves (Grosvenor 1998), as these leaves have a high water content (PBS Nature 2013).  

Up until about nine months, baby koalas only drink their mother’s milk (Grosvenor 1998).  After that point, baby koalas slowly start to wean off milk.  During this stage, baby koalas feed on their mother’s liquefied feces, called pap.  This substance provides the young koala with the necessary microorganisms needed to digest eucalyptus leaves(Encyclopedia of Life 2013).  When a koala is one year old, it no longer needs it’s mother’s milk as a source of nutrients and can survive off a diet of mostly eucalyptus leaves (Grosvenor 1998).  This is when the baby koala leaves its mother.

To view a short clip of a mother koala eating eucalyptus leaves click here