Koala Food & Diets

The Koala Diet

Eucalypt leaves are generally regarded to be highly toxic to animals.  They are quite low in protein and quite high in substances generally regarded as being extremely indigestible to most digestive systems, such as terpene and phenolic compounds. Despite this it remains the staple food for the koala. 

This is believed to have happened in an evolutionary manner when eucalypt trees were even more prolific in Australia than they are even today, and the koala happened to have discovered a niche food source that was unchallenged by any other species.

Metabolism

The koala, as does a wombat, has a quite low metabolic rate, and as a result it remains motionless for most hours of the day.  It sleeps most of that time, as the stomach and intestines slowly do their work of extracting what little protein there is from the eucalypt leaves to give it the energy it needs to survive.  That being said the koala is capable of quite fast aggressive action if sufficiently roused and can be quite quick in scampering along the ground between trees when it is most vulnerable to attack.  They can also be aggressive between each other at times but this is usually short lived.

Feed times

They feed at any time of the day and night for about three of their active five hours whilst awake.  During this time they eat approximately 500g of eucalypt leaves which they chew to an extremely fine paste prior to swallowing.  Its liver then goes about its work deactivating the toxic compounds while the large intestine, which is greatly enlarged, extracts the most nutrients it can from the extremely poor quality diet. 

Most of this breaking down work is done through the process of bacterial fermentation.  The ability to digest in this manner is what is passed down by the mother during the weaning process when the young joey first starts leaving the pouch to feed on the mothers ‘pap’.

Leaf varieties

A koala can digest a wide range of eucalypt leaves, even the leaves of some other plant species, such as; wattle, myrtle, tea tree, melaleuca and paperbark.  Its preferences even change from one area to another, as in the south the Swamp Gum, Blue Gum and Manna Gum is the taste of preference, whereas in the north they prefer Tallowwood and Grey Gum.  Along the great Australian inland river systems and even into their seasonal swamp land koalas can be found enjoying the leaves of the Red Gum, right out into the most arid of outback regions.

There is a total of 680 different species of eucalypt that the koala can eat and it seems they remain strongly in favour of larger trees but put off with trees having leaves with too high a concentration of formylated phloroglucinol (PSM) compounds or too low a concentration of nitrogen.  It therefore appears that the koalas diet is strongly influenced by plant chemistry which seriously limits its food availability, which in turn increasingly limits its population growth potential as our forests decline through increased farming and harvesting practices.