Koalas

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Name
The koala's scientific name, phascolarctos cinereus, comes from phaskolos meaning 'pouch' and 'arktos' meaning bear. The cinereus part means 'ash-coloured'. Some people refer to the koala as a koala bear, but this is incorrect, since koalas are not part of the bear family. This mistake goes back to the early 1800s when the taxonomy of the koala was not fully understood. The word "koala" comes from an Aboriginal word meaning "does not drink." This again is technically incorrect - koalas do occasionally drink. They do, however, gain most of the water they need from their food and from dew that has formed on leaves.

Koalas are found all along the eastern coast of Australia  and as far inland as there is enough rainfall to support suitable forests.Where suitable trees are widely spaced koalas need to spend too much time on the ground to avoid the attention of predators. They are absent from Tasmania.

Physical description
Variations in koalas can be seen across even individual populations. However, the main observable difference is in size and colouration, with those in the south generally being heavier, darker and with longer fur  than those in the north. This difference is due to climate - the climate of Victoria being significantly cooler than that of Queensland - and leads to southern males (12Kg) weighing nearly twice that of their northern cousin (6.5Kg)

The koala's nearest living relative is the wombat, and this is easy to see. However, koalas have developed a thicker, softer coat, much larger ears, and longer limbs, which are equipped with large, sharp claws to assist with climbing, all adaptations for their arboreal life. Weight extremes are about 14 kg for a large, southern male, to about 5 kg for a small northern female. They are usually silent, but males have a  loud groan-like call  used for announcing it's  presence during the breeding season and females emit a similarly loud 'scream' when feeling threatened by the presence of a male. Koalas life span is roughly 8-10 years in the wild and 10-12 years in captivity.

Ecology and behaviour
Koalas live almost entirely on eucalyptus leaves, on average eating 500 to 1000 grams  (1.1 to 2.2 pounds) each day. This is likely to be an evolutionary adaptation that takes advantage of an otherwise unfilled ecological niche, since eucalyptus leaves are a poor food source, being low in protein, high in indigestible substances, and indeed  would be toxic to most other species. Koalas are one of only three species (the others being the ring tailed possum and one of the glider family) that can exist entirely on gum leaves. Because of the low amount of energy that is derived from this food koalas have developed a very low metabolic rate compared to other mammals (which saves energy) and rests for about 20 hours a day, sleeping most of that time. They will feed at any time of day, but usually at night. The liver neutralizes the toxic components and the greatly enlarged hind gut  extracts the maximum amount of nutrition from the leaves. When young koalas are being weaned, the mother passes unusually soft faeces, called pap, on which the young feed. This pap is rich in the bacteria which help neutralize the toxic components of the leaves, and thus these essential digestive aids are passed onto her offspring.

Female koalas are generally solitary but spend much of their adult lives with young. They have distinct home ranges which only tend to overlap in the more fertile areas. These territories will be larger where food is scarce. Although males are not regarded as territorial, they do not tolerate each other, especially during the breeding season when dominant males attack subordinate ones. Most adult males carry scars about the head and arms as a result.

Koalas are almost completely tree dwelling. They make use of a large bony plate in the lower back to rest comfortably  in a tree fork or on a branch. They have long claws and a powerful grip which they use for climbing easily through trees. Motion is normally sedate but can be surprisingly rapid when required. The are comfortable hopping between branches and when on the ground will break into a gallop if threatened, whence they will rapidly climb the nearest tree and wait patiently for the danger to pass. If a predator follows the koala up a tree it is not unusual for the koala to urinate on its follower in order to deter it. Koalas are proficient swimmers, although this behaviour is rarely witnessed.

Reproduction
Males reach sexual maturity at 3 to 4 years old, females at 2 to 3 years. If the female remains healthy and the food supply is adequate, a female koala can produce one young each year for the remainder of her life. Mating normally happens between December and March, the Southern Hemisphere's summer, and gestation is 35 days.

The baby koala is known as a joey and is hairless, earless and blind. At birth the joey, the size of a jelly bean, crawls into the mother's downward-facing pouch and attaches itself to one of the two teats. The teat will then swell into the joeys' mouth, thus preventing it from becoming detached. Here it remains hidden for about six months, only feeding on milk. By the end of this period the joey will have grown eyes and ears and will then start to emerge from the pouch for the first time. It is at this time that the joey will feed on it's mothers' pap. Weaning will not be complete for another six months, during which time the joey will stay close to its mother, usually either on her back or chest. Over this period its diet will gradually change until it is exclusively feeding on gum leaves. Young males may stay within their  mother's home territory until they are two or three years old.

Conservation status
The koala has long been hunted by aborigines for food but was hunted close to extinction by European settlers in the early 20th century, largely for its fur. Indeed, by the 1920s the koala was absent from South Australia and close to extinct in Victoria. Hunting of koalas was outlawed across Australia in the 1930s. Since then the threat to koalas has come mainly from habitat loss. Koalas rely on large areas of connected corridors of forest for a continuous supply of fresh leaves but pressure for alternative land uses (housing, farming, roads etc) has led to widespread fragmentation of eucalyptus forests. These remaining patches of forest are often not of sufficiently high quality  for a population to remain healthy. Other threats to koalas have come from the spread of disease (chlamydia), from road traffic and from domestic and feral dogs. There is little agreement as to the actual number of wild koalas but it is accepted that the population is in decline and  remains well down on the pre-large-scale hunting days.

There are many island and isolated populations where koala populations have flourished to such an extent that some regard them as a pest due to the damage inflicted on trees. Kangaroo Island, in South Australia, introduced koalas early in the 20th century in order to help protect the species. Here they have thrived due to the lack of competition and predation, the estimated population now being approximately 30,000.  Many blame this "over-population " for the widespread destruction of local gum species and so have called for a cull to bring the population down to a more "manageable" 10,000. However, there is much disagreement on the way forward, with others suggesting the cause of tree death is in fact disease and suggesting that the problem is not too many koalas but too few trees. They suggest the way forward is tree protection and tree planting rather than culling. So far culling has proved politically unacceptable as there would undoubtedly be an international backlash. Sterilization and re-location programmes have so far had only limited success in reducing numbers and remain expensive.

Main sources for this information:
Koala: Origins of an icon. Stephen Jackson
Wikipedia
The Australian Koala Foundation web site
Mammals of Australia, Menkhorst and Knight.

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