Koala

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Koalas :: Koala_Lumpur_-_Journey_to_the_Edge

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. Koala - American Heritage Dictionary Closely related words appear in other Australian Aboriginal languages, including:

In the Blue Mountains of New South Wales, Aborigines called Koalas by the word Cullawines.
Near Sydney, Aborigines called Koalas by the word Koolahs.
In the Murray Region, Aborigines called Koalas by the word Karbors.
Other Aboriginal names for Koalas include: Bangaroos, Koolewongs, Narnagoons and Colos. "The Koala", Burton, Barbara, Lone Pine Sanctuary & Fisheries and Wildlife Department, Lansdowne Press (1974).

It is commonly said that the common name 'Koala' is an Aboriginal word meaning "no drink." 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 part of the bear family. The Koala's scientific name comes from the Greek: phaskolos meaning "pouch" and; arktos meaning "bear". The cinereus part is Latin and means "ash-coloured".

Taxonomy and evolution

Although three subspecies have been described, these are arbitrary selections from a cline and are not generally accepted as valid. Following Bergmann's Rule, southern individuals from the cooler climates are larger. A typical Victorian Koala (formerly P. cinereus victor) has longer, thicker fur, is a darker, softer grey, often with chocolate-brown highlights on the back and forearms, and has a more prominently light-coloured ventral side and fluffy white ear tufts. Typical weights are 12 kg for males and 8.5 kg for females. In tropical and sub-tropical Queensland, however, the Koala is smaller (at around 6.5 kg for an average male and just over 5 kg for an average female), a lighter, often rather scruffy grey in colour, and has shorter, thinner fur. In Queensland the Koala was previously classified as the subspecies P. cinereus adustus, and the intermediate forms in New South Wales as P. cinereus cinereus. The variation from one form to another is continuous, and there are substantial differences between individual Koalas in any given region such as hair color.

Koala fossils are quite rare, but some have been found in northern Australia dating to 20 million years ago. During this time, the northern half of Australia was rainforest. The Koala did not specialise in a diet of eucalyptus until the climate cooled and eucalyptus forests grew in the place of rainforests. The fossil record indicates that before 50,000 years ago, Giant Koalas inhabited the southern regions of Australia. The Koala fills the same ecological role as the sloth of South America. Its origins are unclear; however, since its pouch opens backwards instead of forwards like most other marsupials, it is theorised that it may have evolved from a burrowing marsupial.

Physical description

The Koala is broadly similar in appearance to the wombat (its closest living relative), but has a thicker, softer 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. Much as the Flamingo's bright color comes from the carotene they eat, the Koala has been observed as smelling like large cough drops due to their diet of eucalyptus.

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."Flannery, T.F., The Future Eaters, An ecological History of the Australasian Lands and People, (Reed New Holland, Sydney, 1994). p.86

It is a generally silent creature, 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.

Ecology and behaviour

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 wean, 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 eucalypti, 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.

Females are solitary and occupy distinct home ranges that they rarely leave. In the more fertile areas, these ranges overlap; in areas where suitable food trees are scarce they tend to be larger and more exclusive. Males are not territorial, but do not tolerate one another, particularly not during the breeding season: dominant individuals attack subordinate ones, and most adult males carry scars on their face, ears and forearms as a result.

The Koala is almost entirely arboreal. It does not make nests, but sleeps in a tree fork or on a branch. It climbs using its powerful claws for grip, usually moving quite slowly but can climb rapidly when needed. The Koala will leap confidently from one tree to another if they are reasonably close together. Its climbing is aided by a pair of thumbs on each paw, and it is the only other animal aside from primates to possess fingerprints. Longer distances are traversed on the ground in a slow but effective waddle. If threatened, the Koala breaks into a surprisingly athletic gallop, heading for the nearest tree and bounding up it to a safe height. There the Koala waits for the intruder to go away with the patience of a creature that routinely sleeps for 18 hours a day. The Koala is also rather adept at swimming, but this has rarely been witnessed.

Reproduction

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. 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.

Conservation status

The Koala was hunted almost to extinction in the early 20th century, largely for its fur. In recent years, some colonies have been hard hit by disease, especially chlamydia. The Koala requires large areas of healthy, connected forest and will travel long distances along tree corridors in search of new territory and mates. The ever-increasing human population of the coastal parts of the continent continues to cut these corridors by agricultural and residential development, forestry and road-building, marooning Koala colonies in decreasing areas of bush. The Australian Koala Foundation has mapped 40,000 km² of land for Koala habitat and claims it has strong evidence to suggest wild Koala populations are in serious decline throughout the species' natural range. Although the species covers a massive area, only 'pieces' of Koala habitat remain. These pieces need to be managed, protected and restored in a coordinated way. Presently, many are being lost to weeds, cleared for agriculture, or carved up by developers. Other threats come from logging, poor management, attacks from feral and domestic animals, disease and roads.

In contrast to the situation on much of the mainland, where populations are declining, the Koalas of many island and isolated populations have reached what some have described as "plague" proportions. On Kangaroo Island in South Australia, Koalas introduced some 90 years ago have thrived in the absence of predators and competition. Combined with an inability to migrate to new areas, this has caused the Koala populations to become unsustainable and threaten the Island's unique ecology. In particular, species of Manna Gum, native to the island, are being stripped by Koalas at a rate faster than they can regenerate, endangering local birds and invertebrates that rely on them, and causing the extinction of at least one isolated population of manna. Koala numbers are estimated at over 30,000, with ecologists suggesting that the Island can sustain 10,000 at most. Although cull has been suggested as a means to reduce Koala numbers, with the South Australian Government seriously considering such in 1996, this has met with fierce opposition both domestically and internationally, and the species remains protected. The popularity of the Koala has made the possibility of a cull politically improbable, with any negative perception likely to impact on tourism and a Government's electability. In place of a cull, sterilisation and translocation programmes have had only limited success in reducing numbers thus far, and remain expensive. There is evidence that Koalas relocated to the mainland have difficulty establishing themselves in the different circumstances. A mooted alternative to the complex sterilisation method, wherein the animal must first be captured, are hormonal implants that can be injected via darts.

The Koala occurs in four Australian states. Under state legislation, the species is listed as Vulnerable in the South East Queensland Bioregion, Vulnerable in New South Wales and Rare in South Australia. The species' national status is under review. The IUCN lists the species as Near Threatened.

Cultural references

In popular Western culture, the animal is usually either depicted as a cuddly innocent, or as a curmudgeon character never terribly impressed by the things he sees around him. Qantas airlines used a Koala who continually complains about the airline's reliability in a series of television commercials. Rugby union team Queensland Reds has the Koala as its logo. An Australian children's show has animated characters headed by The Koala Brothers. Eminent cartoonist Patrick Cook has periodically depicted the koala as a wine-swilling creature of homicidal, rather than merely curmudgeonly, inclinations.

Koalas as pets

In spite of their looks, people generally do not have Koalas as pets. This is as they are unsuited to a suburban environment, and as it is actually illegal in Australia to do so.

References

Ben Fordham, "Koala cull: the Kangaroo Island controversy", A Current Affair (15 April 2004).

Mammals of Australia | Vombatiforms | Australian Aboriginal terms

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