Koala
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[Photo] Koala looks down, Kangaroo Island. Source http://www-personal.umich.edu/~popec/images/au_08.jpg, Date May, 2002. Author Cody Pope

The Koala (Phascolarctos cinereus) is a thickset arboreal marsupial herbivore native to Australia, and the only extant representative of the family Phascolarctidae.

The Koala is found all along the eastern coast of Australia from near Adelaide to the southern part of Cape York Peninsula, and as far into the hinterland as there is enough rainfall to support suitable forests. The Koalas of South Australia were largely exterminated during the early part of the 20th century, but the state has since been repopulated with Victorian stock. The Koala is not found in Tasmania or Western Australia.

Names
The word "koala" comes from the Dharuk word gula.[3] Closely related words appear in other Australian Aboriginal languages, including:

The Ngunnawal of the Canberra region also call it gula.
In the Blue Mountains of New South Wales, Aborigines called Koalas by the word Cullawines.
In the Murray Region, Aborigines called Koalas by the word Karbors.
Other Aboriginal names for Koalas include: Bangaroos, Koolewongs, Narnagoons and Colos. [4].
It is commonly said that the common name 'Koala' is an Aboriginal word meaning "no drink." [dubious ??? see talk page] The Koala actually does drink water, but only rarely, due to its diet consisting of eucalyptus leaves, which contain sufficient water to obviate the need for the Koala to climb down for a drink.

Early European settlers to Australia called the Koala the Native Bear and the Koala is still sometimes called the Koala Bear, although it is not even a placental mammal (like bears and most other mammals) - it is a marsupial. The Koala's scientific name comes from the Greek: phaskolos meaning "pouch" and; arktos meaning "bear". The cinereus epithet is Latin and means "ash-coloured".

Physical description
The Koala is broadly similar in appearance to the wombat (its closest living relative), but has a thicker, more luxurious coat, much larger ears, and longer limbs, which are equipped with large, sharp claws to assist with climbing. Weight varies from about 14 kg for a large, southern male, to about 5 kg for a small northern female. Contrary to popular belief, their fur is thick, not soft and cuddly. Koalas' five fingers per paw are arranged with the first two as opposable thumbs, providing better gripping ability.

The Koala has an unusually small brain, with about 40% of the cranial cavity being filled with fluid, while the brain itself is like "a pair of shrivelled walnut halves on top of the brain stem, in contact neither with each other nor the bones of the skull. It is the only animal on Earth with such a strangely reduced brain."[5]

It is a generally silent animal, but males have a very loud advertising call that can be heard from almost a kilometre away during the breeding season. There is little reliable information about the lifespan of the Koala, but in captivity they have been observed to reach the age of 15 years.

Life cycle
Females reach sexual maturity at 2 to 3 years of age, males at 3 to 4 years. If healthy, a female Koala can produce one young each year for about 12 years. Gestation is 35 days; twins are very rare. Mating normally occurs between December and March, the Southern Hemisphere's summer.

A baby Koala is referred to as a joey and is hairless, blind, and earless. At birth the joey, only the size of a jelly bean, crawls into the downward-facing pouch on the mother's belly (which is closed by a drawstring-like muscle that the mother can tighten at will) and attaches itself to one of the two teats. The downward-facing pouch provides a much shorter trip from the birth canal to the pouch than in other marsupials. Thus, the forearms need not be as developed for the journey into the pouch, and can develop more fully for excellent climbing ability later in life. Young remain hidden in the pouch for about six months, only feeding on milk. During this time they grow ears, eyes, and fur. The joey then begins to explore outside of the pouch. At about 30 weeks it has begun to eat the semi-liquid form of the mother’s excrement called "pap". The baby Koala will remain with the mother for another six months or so, riding on her back, and feeding on both milk and gum leaves until weaning is complete at about 12 months of age. Young females disperse to nearby areas at that time; young males often stay in the mother's home range until they are two or three years old.

Ecology and behavior
The Koala lives almost entirely on eucalyptus leaves. This is likely to be an evolutionary adaptation that takes advantage of an otherwise unfilled ecological niche, since eucalyptus leaves are low in protein, high in indigestible substances, and contain phenolic and terpene compounds that are toxic to most species. Like wombats and sloths, the Koala has a very low metabolic rate for a mammal (which conserves energy) and rests motionless for about 19 hours a day, sleeping most of that time. Koalas spend about 3 of their 5 active hours eating. It feeds at any time of day, but usually at night. An average Koala eats 500 grams of eucalyptus leaves each day, chewing them in its powerful jaws to a very fine paste before swallowing. The liver deactivates the toxic components ready for excretion, and the hind gut (especially the caecum) is greatly enlarged to extract the maximum amount of nutrient from the poor quality diet. Much of this is done through bacterial fermentation: when young are being weaned, the mother passes unusually soft faeces, called pap, which is rich in these bacteria, thus passing these essential digestive aids onto her offspring.

The Koala will eat the leaves of a wide range of eucalypts, and occasionally even some exotic species, but it has firm preferences for particular varieties. These preferences vary from one region to another: in the south Manna Gum, Blue Gum and Swamp Gum are favoured; Grey Gum and Tallowwood are important in the north, and the ubiquitous River Red Gum of the isolated seasonal swamps and watercourses that meander across the dry inland plains allows the Koala to exist in surprisingly arid areas. Many factors determine which of the 800 species of eucalyptus trees the Koala eats. Among trees of their favourite species, however, the major factor that determines which individual trees the Koala chooses is the concentration of a group of phenolic toxins called formylated phloroglucinol compounds.

http://en.wikipedia.org/wiki/Koala

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