The koala lives within the temperate to sub-tropical zones of eastern Australia. Its habitat is eucalypt woodland and bushland, but of the several hundred species of eucalyptus ("gum trees"), koalas prefer about 60 varieties, with their specific preferences being limited to a couple of dozen.

Koalas are particular to Eastern Australia, and can be found along the eastern and south-eastern coastal regions. They live in cool temperate zones, right up to hot, sub-tropical zones. Koalas live in a range of habitats, as long as there are abundant eucalyptus trees of the sort they prefer. They are found on coastal islands, tall eucalypt forests, bushland and low woodlands inland.

Koalas spend most of their time nestled in the branches of their favoured trees. They do not shelter in tree hollows or nests, but sit comfortably wedged in between tree branches.

Koalas are not found in rainforests, nor in grasslands or deserts. These biomes do not support the eucalyptus trees which koalas favour. They are also not found in Alpine or snowy regions.

The koala is a marsupial mammal which means it has a pouch and suckles its young. Koalas have grey fur and have large rounded ears on top of a big head. They are usually only approximately 60-85cm tall with a stout body and short legs used for climbing. Their size, colouring and shape vary depending on geographic range, for example, southern koalas have thicker and darker fur and are generally larger than those in Queensland which have short, paler grey fur. Males weigh between 6-10 kilograms compared to females who are slightly smaller and range between 5-7 kilograms. Males can also be distinguished by a small bare patch in the middle of the chest which is often stained brown, especially during breeding season. Koalas are closely related to the wombat.

Koalas are considered arboreal (tree dwelling) mammals however they do descend to the ground to move from one tree to the other. Being mostly nocturnal, a koala will spend most of its time sleeping in branches throughout the day and feed mostly at dusk (they sleep for around 18 hours each day). Although koalas are mostly active at night, they will move around during the day. They will move if they are disturbed, if they are too hot, too cold or simply to find a new feed tree. During the day, they tend to move mid-morning (10am-11am) and late afternoon (3pm-4pm).

Koalas are mainly solitary animals except during the mating season. They communicate through a variety of calls consisting of bellows, grunts and low pitched snarls. These calls are often heard during the mating season.

The Koala is the only mammal, other than the Greater Glider and Ringtail Possum, which can survive on a diet of eucalytus leaves. Eucalyptus leaves are very fibrous and low in nutrition, and to most animals are extremely poisonous. To cope with such a diet, nature has equipped koalas with specialised adaptations.

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. Koalas also sleep somewhere between 18 and 22 hours each day in order to conserve energy.

The Koala's digestive system is especially adapted to detoxify the poisonous chemicals in the leaves. The toxins are thought to be produced by the gum trees as a protection against leaf-eating animals like insects. Trees which grow on less fertile soils seem to have more toxins than those growing on good soils. This could be one reason why koalas will eat only certain types of eucalypts, and why they will sometimes even avoid them when they are growing on certain soils.

Photos by August, Hsueh-Cheng Ho

Koalas have a special fibre-digesting organ called a caecum. Other animals, such as humans also have a caecum, but the koala's is very long (200 cms). The caecum contains millions of bacteria which break down the fibre into substances which are easier to absorb. Even so, the koala is still only able to absorb 25 per cent of fibre eaten. Water is also absorbed from the gumleaves, so that koalas rarely need to drink, although they can do so if necessary, such as in times of drought when the water content of the leaves is reduced.

P.Schouten, From 'Koalas, the little Australians we'd all hate to lose' Bill Phillips AGPS

Each koala eats approximately 200 to 500 grams of leaves per day. The teeth are adapted to deal with their specialised diet. The sharp front incisors nip the leaves from the tree. The molars, or back teeth 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.

Koalas are very fussy eaters and have strong preferences for different types of gum leaves. In Australia there are over 600 types of eucalypts, but koalas will not eat a large proportion of these. Within a particular area, as few as one, and generally no more than two or three species of eucalypt will be regularly browsed. (we call these "primary browse trees") while a variety of other species, including some non-eucalypts, appear to be browsed occasionally or used for just sitting or sleeping in.

Different species of eucalypts grow in different parts of Australia, so a koala in Victoria would have a very different diet from one in Queensland. Also, just think how boring it would be to eat the same thing every day. Koalas like a change, too, and sometimes they will eat from other trees such as wattle, tea tree or paperbark.

Koalas or koala-like animals probably first evolved on the Australian continent during the period when Australia began to drift slowly northward, gradually separating from the Antarctic land mass some 45 million years ago. Fossil remains of koala-like animals have been found dating back to 25 million years ago.

As the climate changed and Australia became drier, vegetation altered until what we recognise as eucalyptus, or gum trees, evolved and koalas became dependent on them for food.

Aborigines are thought to have arrived in Australia 60,000 years ago or more. Koalas, like all Australian animals, were an important part of Aboriginal culture and feature in many of their myths and legends.

They were a readily available source of food but koalas remained abundant over their range before the arrival of Europeans with the First Fleet in 1788.

Illustrations by J. Morrison, from Bill Phillips: 'The little Australians we'd all hate to lose'

John Price was the first European to record koalas. He described them in his account of a journey into the Blue Mountains near Sydney in 1798. The koala was given its scientific name, phascolarctos cinereus, meaning 'ash grey pouched bear' in 1816. Subsequently, it was discovered that the koala was not a bear at all, but a member of a specialised group of mammals called 'marsupials', which give birth to immature young and carry them in a pouch. Today, most marsupials are found in Australia and Papua New Guinea.

'Koala' is thought to mean 'no drink' in the Aboriginal language, although there are many different languages spoken by Aboriginal people throughout the country. The name for koala appears in diverse forms in the written accounts of early settlers as cullewine, koolewong, colo, colah, koolah, kaola, koala, karbor, boorabee, and goribun.

As the new colony progressed, the clearing of forests for farmland began, and with it the beginning of the loss of habitat to the native animals. European settlers identified the koala as a source of fur to trade, and in the ensuing years up until the 1930's, millions of koalas were shot for their pelts.

From Bill Phillips: 'The little Australians we'd all hate to lose'

By 1924 koalas were extinct in South Australia, severely depleted in New South Wales, and estimates for Victoria go as low as 500 animals. At this time, the focus of the fur trade moved north to Queensland. In 1919 the Qld Government announced a six month open season on koalas, and in that period alone, 1 million koalas were killed. Although the season officially remained closed until 1927, when the season re-opened, over 800,000 were slaughtered in just over 1 month. Public outrage at the slaughter forced governments in all states to declare the koala a 'Protected Species' by the late 1930's. However, no such laws were brought in to protect the gum trees upon which koalas rely for their food and shelter. Except for some recently implemented laws in NSW, this remains the case throughout the koala's range.

The breeding season for koalas runs roughly from August to February. This is a time of increased activity, and sound levels increase as males bellow more frequently. This is also when the young from the previous year are dispersing from their mothers. Where koalas live near suburban settlements and major roads, this period heralds the busiest time for koala carers, as koalas on the move cross paths with cars and dogs, and accompanying stress levels mean a higher incidence of sickness.

Females generally start breeding at about three or four years of age and usually produce only one offspring each year. However, not all females in a wild population will breed each year. Some produce offspring only every two or three years, depending on factors such as the age of the female and the quality of the habitat. In the average female's life span of about twelve years, this means that one female may produce only 5 or 6 offspring over her lifetime.

Once a female has conceived it is a short 35 days before the birth of the new baby, called a "joey". 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.

The joey makes its way from the birth canal to the pouch completely unaided, relying on its already well-developed senses of smell and touch, strong forelimbs and claws and an innate sense of direction. Once inside the safety of the pouch, it attaches itself to one of the two teats, which swells to fill its mouth. This prevents the joey from being dislodged from its source of food. The mother contracts her strong sphincter muscle at the pouch opening to prevent the baby from falling out.

P.Schouten, From 'Koalas, the little Australians we'd all hate to lose' Bill Phillips AGPS

The young koala drinks only mother's milk for the first six to seven months and remains in the pouch for that time, slowly growing and developing eyes, ears, fur etc. At about 22 weeks, its eyes open and it begins to peep out of the pouch. From about 22 to 30 weeks, it begins to feed upon a substance called "pap" which the mother produces in addition to milk. Pap is a specialised form of faeces, or droppings, which forms an important part of the young koala's diet, allowing it to make the transition from milk to eucalyptus leaves, rather like a human baby is fed "mushy" food when it starts to eat solids. Pap is soft and runny and thought to come from the caecum. It allows the mother to pass on micro-organisms present in her own digestive system which are essential to the digestion of eucalyptus leaves, and is a rich source of protein.

The joey leans out of the pouch opening on the centre of the mother's abdomen to feed on the pap, stretching it open towards the source of the pap, and therefore 'downwards' or 'backwards'. This is why koalas are sometimes said to have a 'backward-opening' pouch, although this is not strictly true.

The baby feeds regularly on the pap and as it grows it emerges totally from the pouch and lies on its mother's belly to feed. Eventually it begins to feed upon fresh leaves as it rides on her back. The young koala continues to take milk from its mother until it is about a year old, but as it can no longer fit in the pouch, the mother's teat elongates to protrude from the pouch opening. Young koalas remain with their mothers until the appearance outside the pouch of the next season's joey. It is then time for the previous year's joey to disperse and find its own home range. If a female does not reproduce each year, the joey stays with her longer and has a greater chance of survival when it does leave its mother.

Females generally live longer than males as the males are more often injured during fights, they tend to travel longer distances with the resulting increase in risks such as cars and dogs, and they more often occupy poorer habitat. Putting a life span on the average koala can be misleading because some survive only for a period of weeks or months, while others survive to old age. Koalas living in an undisturbed habitat would have a greater life expectancy than those living in suburbia. Some estimates for the average life-span of an adult wild male koala are ten years, but the average survival rate for a dispersing sub-adult male living near a highway or a housing estate is closer to two or three years.