KOALA
(Phascolarctos cinereus)

Description
The koala reaches maximum length of 50-82cm and has a lifespan of about 18 years for females and probably several years less for males.  It has a large, round head with large, round, furry ears and a stout body covered with thick ash-grey to deep brown fur with patches of white on the chest and neck, inside the arms and legs and inside the ears.  Koalas have a vestigial tail. The legs are short and the feet large. On the front paw, two fingers are opposed to the other three, rather like a human's thumb, so they can be moved in opposition to the fingers. This allows the koala to grip more securely. On the hind paw, there is no claw on the big toe, and the second and third toes are fused together to form a 'grooming claw'.

Males are larger than females and are more aggressive. An adult male koala can weigh between 8 and 14 kilograms and a female between 6 and 11 kilograms. Mature males are recognisable by the brown 'scent gland' in the centre of their white chest, which is used to mark the base of trees within its territory.

Koalas from the southern part of the distribution, where they have adapted to the colder climate by an increase in body weight and thicker fur, are much larger than those from the most northern part.

Distribution
Koalas inhabit cool-temperate to tropical wet and dry eucalypt forests and woodland. They are found in Queensland, New South Wales, Victoria and South Australia. Their range extends from the Atherton Tableland west of Cairns in Queensland to islands off the coast of Victoria and South Australia in the south, and west to central and western Queensland, New South Wales and Victoria.

Diet
Koalas feed almost exclusively on the leaves of eucalypts and will eat only 120 of the 700-800 species of eucalypt found in Australia. Seasonal preference is shown for many of those eaten. Research has shown that socially stable koala populations occur only when there are favourite tree species present. Even if a selected species occurs within an area, the koala population will not use it unless one or two other favourite species are available.

Koala is an aboriginal word meaning “no drink”. Eucalyptus leaves have a high water content reducing the need for koalas to drink. However, despite popular belief, the koala does drink water.  Eucalyptus leaves are high in fibre and low in protein and to most animals are extremely toxic. The leaves contain strong-smelling oils, phenolic compounds and sometimes cyanide precursors. The oils and phenolic compounds are detoxified in the koala liver. Koalas have an enlarged caecum (similar to the human appendix) in which fermentation of the eucalyptus leaves occur.

A very slow metabolic rate allows koalas to retain food within their digestive system for a relatively long period of time, maximising the amount of energy able to be extracted. At the same time, this slow metabolic rate minimises energy requirements and they will sleep for up to 18 hours per day in order to conserve energy. They may show some activity by day but usually spend the daylight hours asleep in the fork of a tree.

Koalas eat approximately 200 to 500 grams of leaves per day. They have sharp front incisors and the molars are shaped to allow the koala to cut and shear the leaves rather than just crush them. A gap between the incisors and the molars, called a 'diastema', allows the tongue to move the mass of leaves around the mouth efficiently.

Breeding
Sexual maturity is reached at two years of age but males seldom have the opportunity to mate before the age of three or four. Mating occurs from October to February.

Females start breeding at about two years of age and usually produce only one offspring each year until about 14 years of age. Females give birth to a single 'joey' after a gestation of 34-36days. Twins are rare. The tiny baby, which is roughly 2 centimetres long and weighs less than 1 gram looks rather like a pink jellybean as it is totally hairless, blind and has no ears.  It makes its way from the urogenital opening to the pouch where it attaches itself to one of the two teats, which swells to fill its mouth. This prevents the joey from being dislodged.

It is interesting to note that the female koalas pouch opens downward much like the pouch of its more terrestrial relative, the wombat.  Having such a pouch would be an asset to Wombats being animals that scoop dirt under their bellies when digging.  It will not catch the dirt.  For Koalas that live high in trees however, it would be a handicap except for a special adaptation that has been developed.  The mother has a strong sphincter muscle at the pouch opening which she contracts to prevent the baby from falling out.

The joey remains in the pouch for about six months. From about 22 to 30 weeks, the weaning process from milk to eucalyptus commences. At this time the females produce a substance called "pap" which the mother produces in addition to milk. This is a specialised form of faeces, is soft and runny and comes from the caecum. It contains micro-organisms present in the mothers digestive system which are essential to the digestion of eucalyptus leaves.

The joey leans out of the pouch opening to feed regularly on the pap and as it grows it emerges totally from the pouch and can be seen feeding as it lies on its mother's belly. Eventually it begins to feed upon leaves as it rides on her back. The young koala continues to take milk from its mother until it is about a year old. At this stage it is too large for the pouch. To compensate the mother's teat elongates to protrude from the pouch opening. Joeys remain with their mothers until the appearance outside the pouch of the next season's joey at which time it is fully weaned

Conservation Status and threats.
Koalas are protected by law in Australia. The conservation status of the species varies across Australia, from secure in some areas to vulnerable or extinct in others. A recent survey showed that there are far fewer koalas in the wild than was formerly thought.

The biggest threat to the Koala population is the human. Fragmentation of habitats by roads, urban development and agriculture alters population dynamics. As the species has such a specialised diet, land clearing is considered to be a major threat.  

Since European settlement, approximately 80% of Australia's eucalypt forests have been decimated. Of the remaining 20% almost none is protected and most occurs on privately owned land. Australian Eucalypt forests are often subjected to bushfires and periods of drought and these add further pressure to the koala populations.

Over 4000 koalas are killed each year by either dogs or cars.  Natural predators of the koala include goannas dingoes, powerful owls, wedge-tailed eagles, and pythons, all of which are most likely to prey upon juvenile koalas.  Feral animals such as foxes and cats are another threat .

Disease
Aside from a range of cancers like leukaemia and skin cancers, there are 4 common koala diseases caused by the Chlamydia organism: 
- Conjunctivitis that can cause blindness, 
- Pneumonia, 
- Urinary tract infections and;
- Reproductive tract infections, which can cause female infertility.

The symptoms of Chlamydia manifest as sore eyes, chest infections, and "wet bottom" or "dirty tail". Different strains of Chlamydia bacteria are thought to cause these diseases.  In 1995, scientists isolated two strains called Chlamydia pecorum and Chlamydia pneumoniae.  The organism exists but is harmless in populations with plenty of resources, but manifests in times of stress, such as happens when habitat is reduced.

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