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Koala ecology

Scientific name

Phascolarctos cinereus

Genus: Phascolarcto – phaskolos meaning pouched; arktos meaning bear (derived from Greek).

Species: cinereus meaning ashy-grey (derived from Latin).

Classification

Koalas are marsupials, a subclass of mammals. They belong to a unique family called Phascolarctidae. They are so different from any other living marsupial that only they belong to this family. Their closest living relatives are wombats.

Conservation status

Under Queensland’s Nature Conservation Act 1992, koalas are listed as 'regionally vulnerable' in the South East Queensland Bioregion (New South Wales border to Gladstone, and west to Toowoomba). Outside of this bioregion, the koala is 'of least concern' (common) in Queensland, but still totally protected.

In the national context, in 2012, the Commonwealth Government listed the koala as ‘vulnerable’ in Queensland under the Environment Protection and Biodiversity Conservation Act 1999 (Commonwealth).

Habitat and distribution

Estimated distribution of koalas in Queensland

Estimated distribution of koalas in Queensland

Koalas live over a range of open forest and woodland communities but ultimately their habitat is defined by the presence of a select group of food trees.  Koalas are found in higher densities where food trees are growing on more fertile soils and along watercourses. They do, however, remain in areas where their habitat has been partially cleared and in urban areas.

The distribution of koalas covers much of Queensland, New South Wales and Victoria, and a small area in South Australia. Over the past 200 years, their distribution does not appear to have reduced, however, individual koala populations have declined. Local extinctions have occurred due to clearing and fragmentation of eucalypt woodlands and forests for agriculture and human settlement. Fossil records indicate that many years ago, the koala inhabited parts of Western Australia and the Northern Territory. There are no fossil records of koalas ever living in Tasmania.

In Queensland, the greatest concentration of koalas is in South East Queensland where they now compete for space with a rapidly growing human population.

Description

Koalas have a large round head with big furry ears and a stout body. They are covered in fur (grey-brown in colour with white fur on the chest, inner arms, ears and bottom). Their nose and the palms of their paws have no fur. Their bottoms enable them to wedge comfortably in tree forks.

Koalas have poor vision and rely heavily on their other senses. Koalas have good hearing which helps them detect predators and other koalas. Their large black nose gives them an acute sense of smell helping them detect other koalas and find their favourite food trees. The male uses a scent gland on his chest to mark trees by rubbing the gland up and down the trunk. The gland oozes a clear, oily, strong smelling liquid.

A matter of size

Victorian koala (left) compared to a Queensland koala (right)

Victorian koala (left) compared to a Queensland koala (right)

Fur colour largely depends on the geographical location of the koala.  Koalas in Queensland are smaller, less furry and lighter in colour than those in southern Australian states. Queensland's female koalas on average weigh between 5 to 6 kg and males weigh between 6 to 8 kg. In Victoria, females average weight is 8.5 kg and males 12 kg.

Claws for climbing

Koala front paws (top) and hind paws (bottom)

Koala front paws (top) and hind paws (bottom)

Koala scratches on a Grey gum (Eucalyptus major)

Koala scratches on a Grey gum (Eucalyptus major)

Koalas have long, strong arms, short powerful legs and large feet with sharp claws for climbing. Koalas are largely considered arboreal (tree dwelling) mammals, however, they usually walk over the ground to get from one tree to another. When koalas are on the ground, they amble awkwardly but can break into a quick gallop when disturbed.

They have two opposable thumbs on their fore paws which allows them to have a better grip, which is essential for climbing tall trees. When climbing, koalas grip the trunk of a tree with both arms and pull upwards (while pushing with their legs). In doing this, koalas leave behind characteristic scratches in the bark of gum trees—clearly seen on smooth-barked gum trees. Stringybarks that have been regularly climbed by koalas will also have the outer layer of weathered bark scratched away, exposing the fresh layer beneath.

Difference between male and female koalas

Male koala (top) a female koala (bottom)

Male koala (top) a female koala (bottom)

The face of a male koala is about one and a half times bigger than a female’s face. Males have larger noses and their chins protrude further. Males also have a large scent gland which shows as a dirty patch on their white chest. This gives them a strong musky odour.

Compared to male koalas, females have smaller faces, a clean white chest and a pouch. The backward facing pouch protects the young while its mother climbs and travels from tree to tree. It also gives the joey easy access for ‘pap’ feeding. Pap is a special runny faeces produced by the mother koala which is full of the bacteria that the joey needs to digest leaves when it is older.

Diet

Koalas only eat eucalypt leaves and a few other related species. They need to consume about 500 grams (approximately two shopping bags) of leaves each day. Most other animals (excluding a range of insects) avoid eucalypt leaves due to the toxicity of the oils they contain.

Eucalypt leaves are toxic, but koalas are able to break down these toxins using a specialised digestive system. First, the leaves are ground into a paste by the koala's heavily ridged molars, allowing any nutrients to be absorbed in the stomach. Toxins in the leaves are isolated by the liver and excreted as waste in their urine and faeces. The residue is then broken down by bacteria in an elongated, coiled sac (the caecum) that branch off the large intestine before any remaining nutrients are digested.

Koalas are fairly sedentary, sleeping up to 20 hours a day, as their specialised diet of eucalypt leaves is low in energy and nutrients. Koalas are mostly active at night (nocturnal) and around dawn and dusk. However, they can be seen moving during the day if they are disturbed or if they get too hot or cold and need to find a new tree.

Behaviour

Koalas are solitary animals living within a network of overlapping home ranges, which allows contact between individuals for mating. Males will try to establish dominance over the home ranges of a number of females during the mating season. These home ranges vary in size depending on the density of the population and the abundance of suitable food trees.

In spring, adult males begin to call as a way of advertising their presence to surrounding koalas. Males will seek out a mate and fight with rival males to establish their dominance.

Reproduction and lifecycle

Males begin to breed at three to four years of age. Females breed when they are two years old, generally giving birth each year.

Following a pregnancy of 35 days, a koala gives birth to a single young (rarely twins). Births usually take place between November and February. The young stays in the pouch for the next six months before emerging for the first time. The joey will then spend between six and 12 months riding on its mother's back.

By 12 months of age, the young is weaned and takes up a home range, which overlaps with its mother, for much of the next year. Between the age of two and three years, these young disperse beyond their original home range to establish their own range, usually during the breeding season.

On average, koalas live to 10 to 12 years of age in the wild. Although females can continue to breed into their 'teens' and may live as long as 18 years, males are thought to have a slightly shorter lifespan.

Chlamydia is a bacterial infection affecting almost all koalas in South East Queensland. The stress-related disease weakens the immune system and can cause blindness and reproductive tract disease which renders female koalas infertile. Koala infertility from Chlamydia infection is one contributing factor to the current decline in koala numbers.

How to spot a koala in the wild

Koalas are among the most easily recognised of all Australian animals, however, they often go unnoticed as they rest wedged in a tree fork, high in a gum tree. From the ground, a koala may appear to be little more than a bump on the tree itself.

The fur on a koala's bottom has a 'speckled' appearance which makes koalas difficult to spot from the ground. The easiest way to discover a koala resting in a tree involves looking down, not up. While a koala sitting in the crown of a tree can be difficult to see, its droppings on the ground are quite obvious. These are small green-brown, fibrous pellets about 20 mm long and as thick as a pencil. The fresher the pellets, the more likely koalas are somewhere overhead.

Another sign that koalas are around is the distinctive call given by males during the breeding season over the summer months. The call is produced as the male 'snores' as he inhales and then gives a loud, deep roar as he breathes out. On a still night, the call can be heard almost a kilometre away. Females may also produce a low-pitched bellow similar to a male to indicate they are ready to mate. They will also 'squawk' and 'wail' during mating.

Koala sounds

Listen to an audio clip of a koala (MP3 audio file, 189K)†

Martin, R.W. and Handasyde, K.A. (1995) Koala Phascolarctos cinereus, in Strahan, R. (ed.), The Mammals of Australia, Reed Books, Sydney.

Martin, R. and Handasyde, K. (1999) The Koala: Natural History, Conservation and Management, New South Wales University Press, Kensington.

Available from the library catalogue

The documents referred to on this page are available from the department’s online library catalogue.

† Requires an appropriate media player

Last updated
11 July 2012