Nature conservation
Koala Species Outline
Species outline
Koala
Scientific name
Phascolarctos cinereus (Phascol = pouched; arctos = bear; cinereus = ashy-grey)
Animal group
Marsupials (the koala is so different from any other living marsupial that it has been placed in a unique family of mammals, Phascolarctidae). Its closest living relatives are the wombats.
Conservation status
In the South East Queensland Bioregion (an area from the New South Wales border to Gladstone and west to Toowoomba in the south and to Murgon in the north), the koala is listed as 'regionally vulnerable' under the Nature Conservation Act 1992. In the rest of Queensland it is "of least concern" (common) but still totally protected.
Description
Koalas are among the most easily recognised of all Australian animals but often go unnoticed as they rest wedged in the fork of a branch, high in a gum tree. From this angle, a koala may appear to be little more than a bump on the tree itself - but many people may not even take the time to look up in the first place.
The easiest way of discovering if a koala is 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 20mm long and as thick as a pencil.
The fresher the pellets, the more likely a koala is somewhere overhead.
When koalas are on the ground they amble awkwardly but can break into a quick gallop when disturbed.
When climbing, koalas grip the trunk of a tree with both arms and pull upward while pushing with their legs. In the process, they leave behind characteristic scratches in the bark of gum trees that are much larger than those made by a possum or glider and could only be confused with the claw marks of a large goanna. These scratches are clearly seen on smooth-barked gum trees. Stringybarks or ironbarks that have been regularly climbed by koalas will have the outer layer of weathered bark scratched away, exposing the fresh layer beneath.
The final 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 it inhales and then gives a load, deep roar as it breathes out. On a still night, the call can be heard almost a kilometre away.
Females may also produce a low-pitched bellow when another koala climbs the tree they are in and will also "squawk" and "wail" when mating.
Illustration of skull/bones
Photo DERM.
Sometimes koala bones are found, particularly near roadsides where they have died after being hit by cars. A koala skull with its squarish sides and flat top is very distinctive while other parts of the skeleton could easily be confused with the bones of a range of other mammals. If you find the remains of a koala you should also look to see if it has an ear tag or even a radio collar. These are fitted to koalas involved in ongoing research programs or when they are released after being rehabilitated. Please report the finding of any remains, collars or tags to the nearest Department of Environment and Resource Management office as it will contribute to DERM's research programs.
Habitat and distribution
Koalas occur over a range of open forest and woodland communities but ultimately their habitat is defined by the presence of a select group of food tree species. The koala's diet is restricted to the leaves of a number of eucalypts and other closely related species.
Koalas occur in higher densities where food trees are growing on more fertile soils and along watercourses but they will also remain in areas where their habitat has been partially cleared.
The distribution of the koala covers much of the eastern states of Queensland, New South Wales and Victoria, and a small area in South Australia. Over the last 200 years their distribution does not appear to have contracted but individual koala populations have declined and local extinctions have occurred as eucalypt woodland and forest have been cleared or fragmented by clearing for agriculture and human settlement.
In Queensland, the greatest concentration of koalas is in the south east where they now compete for space with a rapidly growing human population.
Diet, behaviour and reproduction
The koala and the greater glider are the only two marsupials that feed on the leaves of a number of gum trees, and a few related species, with the koala having an intake of about 500 grams of leaves each day. Most other animals (excluding a range of insects) avoid eucalypt leaves given the toxicity of the oils they contain.
While eucalypt leaves have evolved to be distasteful and even toxic, the koala has taken up the evolutionary challenge to break down these toxins and use these leaves as a food source. To do this, the koala has evolved a specialised digestive system. First, the leaves are ground into a paste by the koala's heavily ridged molars, making most of their nutrients available for absorption in the stomach. Any toxins in the leaves are isolated by the liver and excreted. The residue is then fermented in an elongated, coiled sac (the caecum) that branches off the large intestine before any remaining nutrients are digested.
Remaining inactive for up to 20 hours a day is also a strategy that helps the koala cope with its low nutrient diet.
Koalas are solitary animals living within a network of overlapping home ranges. Overlapping home ranges allow contact between individuals for mating with a single male establishing his 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.
Females begin to breed at two years of age, giving birth each year. Failure to breed over two years is often a sign that the koala has a chlamydial infection rendering it infertile. Koala infertility from chlamydia is one contributing factor to the current decline in koala numbers.
Following a gestation period of 35 days, a koala gives birth to a single young, or rarely twins. Births usually take place between November and February. The young stays in the pouch for the next six months then emerges and spends an increasing amount of time riding on the mother's back.
By 12 months the young is weaned and takes up a home range that overlaps with its mother for the next year. Between the age of two and four years these young disperse, usually during the breeding season.
Females can continue to breed into their 'teens' and may live as long as 18 years. Males are suspected to have a slightly shorter lifespan.
Threatening process
The biggest threat facing koalas is habitat loss. Much of the koala's habitat overlaps with those parts of Queensland where the most clearing has occurred for urban, industrial and rural development. In South East Queensland, The South East Queensland Regional Plan 2005-2026 projects an annual population growth of between 40,000 and 60,000 people each year and this is placing considerable pressure on the area's remaining koala habitat.
The removal of individual trees is further whittling away this remaining habitat and exposing these areas to secondary threats including weed infestations, inappropriate frequencies and intensities of burning and incompatible management practices, and the longer-term impacts of drought and climate change.
As habitat patches become smaller and more fragmented, koalas are more likely to move through developed areas where they have to cross roads and enter properties where they can be attacked by dogs or even drown in backyard swimming pools.
Next to habitat clearing, the next most serious threat is death from vehicle strikes. In South East Queensland more than 320 koalas each year are killed in vehicle-related accidents.
An average of more than 230 koalas are delivered each year to the two koala hospitals in South East Queensland due to attacks by dogs. Further, between 1997 and 2008, an average of more than 130 koalas were killed by dogs each year. While this level of koala mortality is less than that due to motor vehicles, it is nonetheless significant for a threatened species, particularly as it is believed that many dog attacks go unreported.
Koalas are also susceptible to a number of diseases with a chlamydial infection being common in many Queensland populations. Where a koala hasn't bred for two successive years it is usually a sign of infertility caused by chlamydial disease.
Information sources
Koalas in Pine Rivers
Shire: distribution, abundance and management
Trees for koalas: coastal south east
Queensland
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.
Last updated: 20 April 2009
