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Episode 314: Koala Encore

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The cute and cuddly koala bear (image from earth.com)

There are few animals more emblematic of Australias marsupials than the cute and cuddly koala bear. Marsupials are thought to have evolved away from eutherians (animals with placentas), 148 million years ago, with the relatives of the modern days marsupials we are familiar with evolving in North American around 90 million years ago. It is suggested that eventually they migrated to South America, then moved to ancient Antarctica, long before it became a frozen continent, crossing into a land mass that would become Australia when it broke away 55 million years ago. These isolated animals then began to evolve into the kangaroos, koalas and Tasmanian devils we know today, to mention just a few. During a deep freeze period in the earth’s history, far ranging tropical forests dried up, leaving a much drier continent when the ice retreated. It was into this new environment koalas evolved, adapting to eat drought tolerant plants like their favourite eucalyptus. They have one of the longest fossil records of any marsupial and are part of a once very ecologically and morphologically diverse family called the Phascolarctidae, of which they are the only remaining member. Their name originates from the Aboriginal word for ‘no drink/no water’, a reflection of how little water they need.

How exactly does an animal get by in arid Australia without drinking you might ask? Well, their specialised diet of eucalyptus leaves means they can obtain most of the water they need from the leaves of this plant, although they will drink water in severe heat waves or bushfires. Koalas are extra specially adapted to eat eucalyptus leaves, as compounds in the plant make them fatally toxic to most animals. Over time, koalas have evolved a combination of specialised dietary enzymes and symbiotic gut bacteria that enable them to digest these tough leaves and extract all the nutrients from them. They also have a highly developed sense of smell that allows them to sniff out the most nutritious leaves; so the big black button nose isn’t just cute, its functional too!

A koala munching on its favourite dinner of eucalyptus leaves (image from reference.com)

Is the future of the koala going up in smoke?

Koalas have had a long and rocky history with humans. In the early 20th century, fur traders almost wiped them out, with an estimated 10 million koalas killed for their pelts. Fortunately, people began to recognise the uniqueness of Australian mammals, and actions were taken to stop the fur trade and begin to conserve them.

European fur traders in the early 1900’s, with several koala skins nailed to the wall behind them. This trade almost wiped the koala out, before conservationists stepped in. (image from www.abc.net.au)

Although their numbers have recovered today, they are classed as vulnerable on the IUCN red list, and their populations are in decline across most of their range in Eastern and South Eastern Australia. Their population densities vary considerable, and there are considerable concerns about those areas with a high number of animals, as they are very susceptible to disease or a serious environmental event like a bushfire.

Dealing with infectious disease is an important part of koala conservation. They are particularly vulnerable to viruses like Koala retrovirus and gammherpesvirus, parasites like Trypanosoma irwini, a serious blood parasite and Chlamydia pecorum, the most significant pathogen affecting this cuddly marsupial. Although the infection can often be asymptomatic, if it persists, koalas can suffer from arthritis, blindness, infertility and respiratory disease; a bleak outcome for an animal already teetering towards endangered status.

There has been significant habitat destruction and urbanisation of coastal areas and conversion of vital eucalypt forest to agriculture across large swathes of Australia. Since European arrival to the continent, 50% of prime koala habitat has been lost. Although research has shown that Koalas can manage habitat change provided there are enough trees present, this still leaves them at huge risk from domestic dog attacks and vehicle collisions. Some parts of Australia have even implemented specialised wildlife highways for their koalas to cross busy main roads.

A sign from an area of Australia facing huge potential deforestation. Many conservationists are fighting to protect large areas of koala habitat (image from www.echo.net)

Like so many species, koalas are particularly threatened by climate change. We all saw the devastating wildfires of early 2020, which saw an estimated 30,000 koalas killed in the infernos that raged across Australia. Koalas are particularly vulnerable due to two major reasons; eucalyptus trees have high oil content, meaning if they catch fire they go up quickly, often leaving unfortunate koalas no time to escape. Secondly, increasing levels of carbon dioxide in the atmosphere have been shown to affect the quality of their eucalyptus food. In elevated carbon dioxide levels, the protein concentration of eucalyptus leaves decreases, leaving the beleaguered koalas with poorer quality, less nutritious food. Droughts will also cause eucalyptus leaves to drop their leaves as a stress response, leaving little resources to spread out amongst the koala population. This can lead to young animals being completely excluded from prime feeding grounds by older, more dominant males, putting them at risk of starvation. They may  look cute, but koalas are pretty antisocial and actually rather grumpy, and won’t think twice of kicking a smaller fellow koala out of the tree.

A stark image of a koala clinging to a burnt tree amidst the devastation of a bushfire. Although bushfires can be a healthy and natural, the extreme, repeated wildfires in Australia are devastating ecosystems, and the koala itself. (image from wwf.org)

Some conservationists actually consider the koala bear to be functionally extinct, which is classed as a species that either can no longer play an effective role in their ecosystem or have reached low enough numbers that they won’t breed enough healthy offspring. Between 2018 and 2021, the koala population dropped by 30%, and there are concerns they have reached a tipping point that means they won’t recover.

Conservation optimism

Although more work needs to be done to secure the future of the koala bear, there are conservation management plans now in place in New South Wales, Victoria and Queensland. Legally, whenever building companies want to build new developments, they have to complete surveys and consider koalas in their plans, such as ensuring sufficient trees and refuge areas for the chilled-out bears to hide away in. In busy urban areas, special ‘wildlife highways’ have been put in place for koalas to cross bustling roads safely. Scientists did not have a lot of hope that koalas would learn to use these highways, considering them to be too dozy and doped out on eucalyptus leaves to figure out anything more complex than their next nap. However, GPS collars and camera traps revealed that koalas used these structures to trundle from one area to the next in search of a eucalyptus dinner. This has benefited not just koalas, but also other species like echidnas, goannas, possums and wallabies.

A Koala using a wildlife passageway to cross a busy road in Queensland. (image from www.bbc.co.uk)

Although some areas have gone to the effort and cost of installing highways, there are still significant injuries to koalas from cars and pet dogs, alongside the serious burns koalas can suffer in forest fires. There are several amazing wildlife hospitals and rehab centres across Australia, including the Australia Zoo Wildlife Hospital, based at Steve Irwin’s world-famous zoo. You can see a tour of the Wildlife Zoo Hospital with Robert Irwin in the videos at the end of this writeup, featuring a cute koala getting first class care after an injury.

A Koala injured in a wildfire being nursed back to health by Dana Mitchell, owner of Kangaroo Island Wildlife Park (image from www.mindfood.com)

There are ongoing habitat restoration efforts across areas devastated by wildfires, led by charities like the Australian Koala Foundation (Home – Australian Koala Foundation (savethekoala.com)). Koalas have been successfully reintroduced into several islands off the coast of Australia, including Philips Island, which houses a conservation  reserve protecting not just koalas but a multitude of other species. Koalas are fantastic ambassador animals for all bush dwelling animals, and if we can protect them and their habitat, we can protect so many other species.

Awesome videos!




Black, K.H. Price, G.J. Archer, M. Hand, S.J. (2014) ‘Bearing up well? Understanding the past, present and future of Australia’s koalas.’ Gondwana Research

Madden, D. Whaite, A. Jones, E. Belov, K. Timms, P. and Polkinghorne, A. (2018) ‘Koala immunology and infectious diseases: how much can the koala bear?’ Developmental and Comparative Immunology

Ogura, T. Nakayama, T. Yamabe, K. Shigeno, H. Tani, Y. Yugawa, M. Shibata, E. Miyakawa, E. and Ohata, M. (2019) ‘Koalas utilise volatile compounds to choose preferred Eucalyptus leaves.’ Journal of Zoo and Aquarium Research

Seabrook, L. McAlpine, C. Baxter, G. Rhodes, J. Bradley, A. and Lunney, D. (2011) ‘Drought-driven change in wildlife distribution and numbers: a case study of koalas in south west Queensland.’ Wildlife Research

Shiffman, M.E. Soo, R.M. Dennis, P.G. Morrison, M. Tyson, G.W. and Hugenholtz, P. (2017) ‘Gene and genome centric analyses of koala and wombat fecal microbiomes point to metabolic specialisation for Eucalyptus digestion.’ PeerJ

Waugh, C. Khan, S.A. Carver, S. Hanger, J. Loader, J. Polkinghorne, A. Beageley, K. and Timms, P. (2016) ‘A prototype recombinant-protein based Chlamydia pecorum vaccine results in reduced chlamydial burden and less clinical disease in free ranging koalas.’ PLOS One




January 11, 2023
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