Koala

Koalas are primarily nocturnal, spending most of their time in the branches of trees where they can feed, rest and gain some protection from ground-dwelling predators (6). Much of a koala's time is spent sleeping, and when awake they are still a fairly sedentary species. An adult consumes about 500g of fresh leaves per day (3). Koalas feed on a variety of trees, but the bulk of their diet comes from only a few eucalypt species (6), with marked local and regional differences for the species of eucalypts preferred (5). Eucalyptus leaves are very fibrous and highly toxic, but koalas have evolved to cope with these problems with special cheek teeth that grind the leaves into a fine paste, which is then digested by microbes in the caecum part of the intestine which is unusually long, at around 200cm, and has a blind end, unlike the caecum in most other mammals. Some of the poisons are detoxified in the liver. The diet does not provide much energy, but the long periods spent sleeping, along with their relatively small brains, help compensate for this (3). There is also evidence that suggests koalas may perform myrecism - regurgitating and re-chewing partially digested food, which extracts more energy from the food (7). Both males and females reach sexual maturity at around two years old, but males are rarely large enough to compete for mating access until four years old. Females normally give birth to one young every year but in older females this may reduce to one every two years. The newborn 'joey' is underdeveloped and crawls rapidly through the mother's fur to her pouch, where it suckles for six months. During weaning, in addition to milk, the joey feeds on a substance called 'pap' which is a liquefied form of the mother's faeces and provides the joey's digestive system with the micro-organisms necessary for digesting the eucalyptus leaves (4). Having first left the pouch during this time, the joey rides on its mother's belly, and later rides on her back. It normally remains with its mother until the following year's joey has emerged from the pouch (3).

Although koalas are a protected species, their numbers have markedly decreased due to habitat loss, and many populations are now living in isolated patches of habitat, putting them at greater risk of localised extinctions. Remaining koala habitat is mostly on privately-owned land so landowners have a responsibility to conserve them. As an important step in its aim to achieve national species-specific legislation that would effectively protect koala habitat over all of the koala's range, in July 2004 the Australian Koala Foundation submitted a nomination to the Australian Government, supported by a large amount of scientific data, to list the koala as Vulnerable nationally as a matter of urgency. To date this has not been achieved. Without legislation that encourages landowners, through incentives, to protect habitat on their land, there are fears koala numbers will decline to such an extent that populations will be incapable of ever recovering (5). Legislation, along with continued research and monitoring, will be necessary to prevent this Australian icon from further declining as a result of competing land use pressures (5).

Koalas are bear-like in appearance, with a stout body and large paws, but are in fact marsupials, not bears. Their fur is predominantly grey to light brown, being lighter and shorter in the warmer north of their range, where the koalas are also smaller (3). The chin, chest and insides of the ears and forelimbs are white, with white speckling on the rump and long white hairs edging the large, round ears. Koalas are adapted to life spent mainly in the trees, with a vestigial tail, and unusually long forelimbs in relation to their hind limbs, and specially adapted paws to aid in gripping and climbing. They have large claws and rough pads on their paws. The first and second digits of the front paws, as well as the first digits of the hind paws, are opposed to the others, like thumbs, to help to grip branches. The first digit of each hind paw has no claw, and the second and third digits are partially fused together to form a grooming claw for removing ticks (5). Males are larger and heavier than females, with a broader face. Mature males are distinguishable from females as they have a brown gland on their chests that produces scent used to mark trees within the territory. Being marsupials, the females have a pouch with a backwards-facing opening and a strong, contracting ring-shaped muscle at the pouch opening which prevents the young from falling out (5).

Koalas live in eucalypt forests and woodlands, from cool-temperate to tropical areas (3).

Populations exist in a band down the eastern and southern coasts and inland areas of Queensland, New South Wales, Victoria and South Australia, as well as on islands off Queensland, Victoria and South Australia (5).

Classified as Lower Risk - near threatened (LR/nt) on the IUCN Red List 2003 (1). Listed as Vulnerable in the southeast Queensland bioregion under the Nature Conservation Act 1992 and as Common in the rest of the state. Classified as Vulnerable under the New South Wales Threatened Species Conservation Act 1995. Victoria has no official listing and in South Australia, koalas are listed as Rare (5).

Koala numbers reached a low point in the 1930s, due mainly to the fur trade, when many local populations, including that in South Australia, became extinct, although they have since been re-introduced to South Australia. Other factors in their decline included land clearing, disease, fire and drought. Whilst the koala population as a whole has recovered somewhat since then, its current conservation status varies across its range (3). Major threats now include land clearing and urbanisation resulting in lost, fragmented and low quality habitats. Koalas are confined by their diet to a specialised habitat of which around 80% has been destroyed since Europeans settled in Australia. They are also threatened by fires, droughts, disease (particularly due to the Chlamydia bacterium), death by road traffic and predation by dog. Recently there has been a lot of attention in the media suggesting that koalas in some isolated patches of habitat have been the cause of defoliation of eucalyptus trees, resulting in calls for a cull of the koalas in these areas. That the koalas are to blame is a contentious issue amongst scientists and authorities and there is evidence to suggest that several other factors may be the cause (5).