Koalas are possibly our most iconic native animals; instantly recognisable worldwide as a symbol of Australia and found nowhere else.
Sadly, their dramatic and continuing decline is perhaps just as symbolic.
Perched high in gum trees, with their stocky, tailless body, large heads and fluffy ears, Koalas live almost entirely on eucalyptus leaves, which are tough to digest.
As a result they’ve developed a very slow metabolism to save energy – in fact they can sleep for up to 20 hours a day!
Weighing 4kg to 15kg, Koalas are among the largest tree-dwelling marsupials and males are up to 50% bigger than females.
Mostly active at night, with their sharp claws and opposable digits, Koalas are most at home high in the tree canopy and come down to ground only to move trees or to another habitat patch. They get all the moisture they need from gum leaves and only need water in times of drought (when leaves dry out).
There are more than 700 species of eucalypts and Koalas are quite fussy eaters – only around 50 are suitable and around a dozen make up their staple diet.
Often they’ll choose to only browse their favourite species or limit themselves to two or three, and they prefer new growth on the tips of branches, which have the softest and juiciest leaves.
Since different eucalypts grow in different parts of Australia, a Koala’s exact diet depends on where it lives. Koalas have fantastic hearing and an even better sense of smell, which is how they choose the best leaves to eat.
Despite their incredible digestive system, they can still only absorb about 25% of the nutrients from the leaves, and the rest is excreted as undigested fibre. So they need to eat a lot of leaves – adults will put away around 500g to 1kg of leaves each night!
For this reason they need to move around a number of trees. Each adult has several home trees in its range, which will overlap with those of other Koalas.
Socialising and breeding
Koalas are not social animals – in fact they’re territorial and adults will generally only tolerate each other when breeding. Mature males have a dark mark in the middle of their chests, which are scent glands that they rub on trees to mark their territories.
Koalas communicate with a range of sounds – the most surprising is a loud belch or bellow. This is the sound males use to call out to females when they’re ready to breed.
Koalas are seasonal breeders, mating in spring through to early autumn. A joey the size of a kidney bean will be born 35 days after mating. It will crawl to its mother’s teat, relying on its strong arms and sense of smell and touch. There it will stay attached for 13 weeks and won’t open its eyes until week 22.
Before it can eat gum leaves, which are toxic for most mammals, joeys feed for a few weeks on their mother’s droppings, which gives them access to micro-organisms from her intestine that are needed to digest the leaves.
At around 7 months they will start climbing on their mothers’ backs and will be independent by their first birthday.
Younger females will usually birth a joey each year. Older animals may only reproduce every two or three years.
Where do Koalas live?
Koalas can be found in Eastern Australia – through much of Queensland (from the Atherton Tablelands west of Cairns moving south), NSW, Victoria and a small section of South Australia.
Thanks to reintroductions, Koalas are still distributed over much of their former range, but numbers have been drastically reduced and populations are becoming fragmented by the reduction in continuous habitat.
Koalas need a lot of space and a lot of trees – about 100 each.
Koalas continue to be most abundant on the central and north coast of NSW and the south east corner of Queensland.
Animals vary in size and colour depending on their location. Those in southern NSW and Victoria are often larger and slightly darker, with thicker fur than northern populations – probably an adaptation to keep them warmer in cooler climates.
Threats to Koalas
Koalas can live 13 to 18 years in the wild, and have few natural predators. Dingoes may prey upon some on the ground and birds of prey such as owls or Wedge-tailed Eagles are threats to young.
However, humans are directly responsible for the decline in Koala numbers since European settlement. Love for these iconic animals was initially expressed through their systematic slaughter, to meet the demand for skins in London.
Australia’s Marsupial Destruction Act (1877) officially sanctioned and encouraged the industry and by 1894 between 10,000 and 30,000 Koala skins were reportedly being exported to London annually.*
The Koala was protected in Victoria in 1898, and NSW in 1903 but despite some protection in Queensland from 1906, the slaughter of Koalas continued. From the last quarter of the nineteenth century to the 1930s there was a thriving trade in the skins of native animals.
One million Koala skins were sold in the open season in 1919 and as many as two million were estimated to have been exported in 1924.**
Today, although Koalas themselves are protected by law, most of the suitable habitat remaining occurs on private land, which is largely unprotected. Woodlands continue to be cleared for agricultural and urban development.
Sadly, with their homes cleared, individuals are vulnerable to be killed by cars or dogs as urban areas encroach on remnant habitat, and climate change is expected to further shrink the suitable habitat available.
With their slow movements, Koalas are also susceptible to bushfires, and can be affected by dehydration during heat waves. Chlamydia is also a significant threat and is more prevalent in stressed populations.
In 2022 the status of Koalas in Queensland and NSW moved from vulnerable to ‘endangered’.
What’s Bush Heritage doing?
We have Koalas on both our Carnarvon Station Reserve and Goonderoo Reserves and they've also been spotted at Currumbin Valley Reserve (all are in Queensland). As staff and volunteers have discovered, Koalas are not always easy to spot!
Despite their size and unmistakable features, they can climb to some of the highest, thinnest tree branches where their silhouettes are broken up by waving foliage and a glary skyline. Combined with their stillness and sleepy habits, they can easily go unnoticed by people working below.
At Goonderoo, we're now rolling out a dedicated monitoring program to pay close attention to the health and dynamics of the local Koala population and their habitat. We also help conserve Koalas by managing the threat of invasive species (predators and weeds) which degrade habitat.
Bush Heritage is very fortunate to have found strong partners in this work. The Fitzroy Basin Association has been extremely generous in funding the purchase of extra monitoring equipment, to be used not only on the Koala surveys but regular surveillance of predator activity. The Nature Refuge Landowner Grant will cover the cost of engaging a Koala expert to support the design of the monitoring program.
Donate today to help us continue this and other vital conservation work. Most of our operating costs are funded by generous individuals. Donations over $2 are tax-deductible and we can't thank you enough for your support.
* R. Lydekker A Handbook of the Marsupulia and Montremata. London. H Allen & Co, 1894.
** Roger Martin & Kathrine Handasyde. THE KOALA Natural History, Conservation & Management, Sydney. UNSW Press. 1999. p. 23