The koala is a tree-dwelling, folivorous marsupial found in scattered populations along the eastern seaboard of Australia – from west of Cairns in far north Queensland through to South Australia. More isolated populations are also found on the tablelands of the Great Dividing Range and the western plains of both Queensland and NSW. Koalas are found across Victoria and populations on mainland South Australia as far as Adelaide. There are also populations relocated from the mainland to islands off Queensland, Victoria and South Australia.
Due to habitat loss, the koala is now under threat, making it a sentinel animal for forest-dwelling species in this country. Basically, if the koala is wiped out, whatever (and whoever) is responsible for its eventual extinction will also precipitate the demise of other fauna and flora. Australia holds the shameful title of having the greatest number of extinctions of mammals in the world.
Even though koalas are seen as solitary animals, they actually live their lives as part of a dynamic, ordered hierarchical system.
Each koala within the population lives in an individual home range. The home range size is dictated by the age, sex and social standing of each koala which includes the amount of trees, how far apart they are located and what use they have. A koala occupies its home range for life unless pushed out through age, infirmity or habitat removal. All home ranges within each population overlap at various points. Koalas also vocalise to each other, so communication for this animal is an integral part of daily life.
The fittest, biggest and most virile male koala is the alpha male. He occupies the best quality habitat, which is usually the largest in size with his territory overlapping the home ranges of 3–4 higher ranking breeding females.
Often there is an alpha female, a healthy, fit, fertile, breeding koala who occupies prime habitat adjacent to the alpha male. It is necessary for all breeding females to obtain good-quality habitat. Lactation takes a lot from an animal living on a low energy/low nutrient diet, so a breeding female’s range must be able to sustain both herself and her young.
There are four main marsupial species that feed on eucalypt leaf – the greater glider, the common ringtail possum, the common brush tail possum and the koala. Both the greater glider and the koala use eucalypts as their principal food source.
Koalas, a monogastric hindgut fermenter, not only have a large and complex digestive system (see Figure 3) to accommodate their diet of eucalypt leaves, their whole lifestyle has evolved around it. Starting with the selection of the right leaf type, the koala grabs a branch, then sniffs the leaf to check its quality (and toxicity level) prior to consumption. The leaf is broken off with a strong biting action, masticated, mixed with saliva to allow enzymes to begin the breakdown process, and then swallowed, before ending up in the stomach.
Koalas “chew” their leaf in a methodical size-reduction process. Provided koalas have unworn, sharp interlocking cusp points on their molars, this is done efficiently. Aged koalas with worn, flat teeth cannot achieve an adequate breakdown of leaf. The result is that such koalas cannot make use of their food and will basically starve to death.
We often get asked why we cannot “cure” some koala diseases and why we cannot give a number of drugs to koalas. Well this is why…..
Eucalypt foliage is very tough and contains a number of chemical compounds designed to protect the tree. These compounds are quite toxic and would kill the majority of animals (or people for that matter) if they decided to eat them. Koalas along with possums and gliders have evolved over millions of years the ability to live on a diet of eucalypt leaves without suffering any issues with the deadly chemical compounds.
So how does a koala cope with the toxins? With a super liver of course!
Koalas have developed an amazing liver that is quite big, has multi lobes and very complex. Its job is to breakdown and excrete all those nasty compounds and eliminate them from the body via the urine.
This liver works so well, that a number of medications that are given to koalas are metabolized, broken down and excreted out before they have any chance of reaching the bloodstream and doing the job they are designed to do.
Chlamydia is an obligate, intracellular bacteria that is found in many species of bird and mammals worldwide.
How does chlamydia occur in koalas?
It is likely that many strains of this disease have existed for a very long time within koala population, acting as natural population regulators. In the early 1800’s Europeans settling in Australia brought with them agricultural livestock such as sheep, cattle and pigs. Records from this period reported koalas “curled up at the base of trees, with diseased eyes and looking very sick”. Research using DNA sequencing has shown that some of the current strains of chlamydia are very similar to those found in cattle, sheep and pigs. It is highly likely that these strains of chlamydia “jumped ship” from agricultural animals into koalas – how this transmission occurred is still largely unknown. These “newer” strains are considered to be more virulent exposing koalas to diseases they have not had enough evolutionary time to adapt to and thus the disease had a major impact on wild koala populations even as far back as the 1800’s. This scenario is similar to our first nation’s people of this country who were first exposed to European diseases in the 1880’s such as influenza with disastrous results.
The second biggest reason for admission to the hospital is koalas being hit by motor vehicles. Depending on the level of trauma to the animals, we have a reasonably good success rate with treating this problem. It is very distressing to admit a healthy, fit young animal who has their whole future in front of them but whose injuries are so bad they die before we can treat them or shortly after arrival.
As motor vehicle injuries are usually quite traumatic to the koala it can often be a long rehabilitative process but every koala is given the best possible chance to recover.
Important:If you believe the koala you saw is injured or in any way distressed, please call our 24-hour Rescue Line immediately on (02) 6584 1522
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