What do koalas eat?
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The koala, (Phascolarctos cinereus), a marsupial native to Australia is most recognized for its distinct diet primarily consisting of eucalyptus leaves. Despite the vast diversity of eucalyptus species, koalas exhibit a fondness for a select few of eucalypts.
Koalas are facing unprecedented threats to their survival, from habitat destruction to climate change. By supporting our efforts, you can help provide the care and protection these iconic animals desperately need. Read on to learn about the vital role of diet in koala health and discover how you can contribute to their wellbeing. Every donation, no matter the size, helps us make a significant impact.
Koalas are facing unprecedented threats to their survival, from habitat destruction to climate change. By supporting our efforts, you can help provide the care and protection these iconic animals desperately need. Read on to learn about the vital role of diet in koala health and discover how you can contribute to their wellbeing. Every donation, no matter the size, helps us make a significant impact.
Koalas and Their Unique Eucalyptus Diet
Koalas rely almost entirely on eucalyptus leaves for food, even though these leaves are tough, low in nutrients, and difficult to digest (Lawler et al., 1998). They also contain natural chemicals called phenolics and terpenes, which are toxic to most animals (Foley, Iason, & McArthur, 1999).
So how do koalas survive on a diet that most animals avoid? They have developed special adaptations that allow them to process eucalyptus leaves efficiently. One key adaptation is their slow metabolism, which helps them conserve energy while digesting this tough diet (Ellis & Bercovitch, 2011).
Another remarkable feature is their unusually long caecum—a part of their digestive system that is the longest relative to body size of any animal. This organ is home to special bacteria that break down the tough plant material, turning it into nutrients the koala can absorb (Osawa, 1990).
Koalas and Their Unique Eucalyptus Diet
Koalas rely almost entirely on eucalyptus leaves for food, even though these leaves are tough, low in nutrients, and difficult to digest (Lawler et al., 1998). They also contain natural chemicals called phenolics and terpenes, which are toxic to most animals (Foley, Iason, & McArthur, 1999).
So how do koalas survive on a diet that most animals avoid? They have developed special adaptations that allow them to process eucalyptus leaves efficiently. One key adaptation is their slow metabolism, which helps them conserve energy while digesting this tough diet (Ellis & Bercovitch, 2011).
Another remarkable feature is their unusually long caecum—a part of their digestive system that is the longest relative to body size of any animal. This organ is home to special bacteria that break down the tough plant material, turning it into nutrients the koala can absorb (Osawa, 1990).
Koalas may rely on eucalyptus leaves for food, but they don’t just eat any leaf they come across. In fact, they are quite selective about what they consume, which is why they are often described as "fussy" eaters.
Research shows that koalas carefully choose their leaves based on nutritional content and the levels of natural plant chemicals, known as secondary metabolites, which can affect digestibility and taste (Marsh, Wallis, & Foley, 2003).
They also tend to prefer leaves from older eucalyptus trees, which are believed to have higher protein content, making them a more nutritious option (Ellis, Melzer, & Carrick, 2002). This pickiness isn’t just about preference—it’s a crucial survival strategy that helps them get the most out of their limited diet.
By being selective, koalas have adapted to thrive on a food source that would be unsuitable for most other plant-eating animals.
Research shows that koalas carefully choose their leaves based on nutritional content and the levels of natural plant chemicals, known as secondary metabolites, which can affect digestibility and taste (Marsh, Wallis, & Foley, 2003).
They also tend to prefer leaves from older eucalyptus trees, which are believed to have higher protein content, making them a more nutritious option (Ellis, Melzer, & Carrick, 2002). This pickiness isn’t just about preference—it’s a crucial survival strategy that helps them get the most out of their limited diet.
By being selective, koalas have adapted to thrive on a food source that would be unsuitable for most other plant-eating animals.
Are there any other plants that they might consider in their diet?
In conditions such as drought or lack of preferred eucalyptus species, koalas may even turn to exotic plant species introduced in their habitats. Furthermore, their partiality towards specific types of bark and wood likely reflects the mineral content within these substances, offering a glimpse into their dietary adaptability under ecological pressures.
Koalas, rather than being a gourmet of eucalyptus, doesn't only limit its diet to this single species. The complexity of the koala diet is seldom spoken of, with them adding other plant genera like Corymbia, Melaleuca, Causarina and Angophora, all of which are directly related to Eucalyptus, particularly when the situation is urgent.
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Favorite Leaves
Koalas' fondness for specific eucalyptus species is well-established. However, their preferences can fluctuate greatly depending on the region due to variations in eucalyptus species availability across Australia.
Still, several eucalyptus species regularly grace the koala's plate:
1. **Eucalyptus camaldulensis** (River Red Gum): Widespread and a koala favorite.
2. **Eucalyptus tereticornis** (Forest Red Gum): Frequently found in koala diets.
3. **Eucalyptus microcorys** (Tallowwood): A popular choice for koalas in New South Wales and Queensland.
4. **Eucalyptus punctata** (Grey Gum): A frequent constituent of the koala's diet in New South Wales and Queensland.
5. **Eucalyptus viminalis** (Manna Gum): A favored food source, particularly among koalas in Victoria and South Australia
6. ** Swamp Gum (Eucalyptus ovata), , River Red Gum (Eucalyptus camaldulensis), Blue Gum (Eucalyptus leucoxylon), Long-leaved Box (Eucalyptus goniocalyx) and Brown Stringybark (Eucalyptus obliqua) - All South Australian favorites
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The Koala's Sense of Smell
Despite the apparent sameness of eucalyptus, koalas demonstrate an uncanny ability to identify and select leaves with higher protein content and fewer defensive chemicals like tannins and phenolic compounds (Marsh, Wallis, & Foley, 2003).
Yet another astounding adaptation is the koala's more effective water conservation method. Given that their habitat is so arid, koalas have evolved to obtain most of their water requirements from eucalyptus leaves and look for alternative water sources only in certain situations but they will drink water if they get a chance to do so. (Ellis & Melzer, 2003).
Despite the apparent sameness of eucalyptus, koalas demonstrate an uncanny ability to identify and select leaves with higher protein content and fewer defensive chemicals like tannins and phenolic compounds (Marsh, Wallis, & Foley, 2003).
Yet another astounding adaptation is the koala's more effective water conservation method. Given that their habitat is so arid, koalas have evolved to obtain most of their water requirements from eucalyptus leaves and look for alternative water sources only in certain situations but they will drink water if they get a chance to do so. (Ellis & Melzer, 2003).
Do koalas eat soil?
While eucalyptus leaves make up the majority of a koala’s diet, they also consume soil—particularly from termite mounds. This behavior is thought to provide essential minerals and digestive enzymes that support their metabolism. In fact, sick koalas have been observed eating soil, leading researchers to suggest they may be "self-medicating" by doing so. Care facilities even offer soil to unwell koalas in bowls to aid their recovery (Gillett et al., 2019).
Soil contains a variety of minerals that eucalyptus leaves lack, making this behavior—known as geophagy—an important dietary supplement. Some researchers also believe that eating soil, especially clay-rich soil, may help koalas detoxify their bodies (Barker et al., 2005).
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Dietary Implications of loving leaf (and needing moisture in the leaf)
Koalas have a highly specialised diet, which gives them an advantage by reducing competition for food. However, this comes with challenges—eucalyptus leaves are low in nutrients and contain natural toxins that koalas must process to survive.
Research suggests that climate change may make eucalyptus leaves even less nutritious, putting koalas at greater risk (Moore et al., 2010).
The water content in fresh eucalyptus leaves can provide a large portion of a koala’s hydration—studies show koalas obtain approximately 74–81% of their daily water intake from leaf moisture alone (Mella, Ward, & McArthur, 2019). But when eucalyptus trees are exposed to heat and drought - and with climate change this is now happening more than ever, so leaves begin to lose moisture—a process known as desiccation. You can think of it like a sponge drying out. At first, the leaves may still feel soft and moist, but over time they become drier and less able to hold water.
Scientists measure desiccation time to understand how long it takes for leaves to dry out once water is no longer available. In one study looking at a range of eucalyptus species, some leaves lost their moisture in just 4 days, while others took up to 14 days to fully dry (Blackman et al., 2019).
This matters because:
- Species with a short desiccation time lose water quickly and become poor sources of hydration for koalas.
- Species with a longer desiccation time hold onto water longer, giving koalas more time to access moist, hydrating leaves—especially during heatwaves or when rainfall is low.
Leaves that dry out quickly are simply less helpful to koalas, especially when droughts last for weeks or months.
During droughts or heatwaves, leaf moisture drops significantly, posing a risk to koalas. In water-stressed trees, leaf moisture may fall to around 50% or lower. Koalas tend to prefer leaves with a moisture content of at least 55–65%, and if leaves fall below this threshold, they may avoid eating them (Ellis et al., 2010). In extreme drought, leaf moisture has been recorded as low as 51% in some habitats—levels that proved insufficient to sustain koalas, with documented fatalities due to dehydration (Ellis et al., 2010).
This problem is a poignant example of how climate extremes impact wildlife: the hardy eucalyptus tree can endure drought by dropping leaves, but the koala then faces a landscape of crunchy, dry leaves that can’t sustain them. Understanding eucalyptus leaf desiccation helps explain why, in tough times, koalas need a helping hand (or a helping sip) to quench their thirst.
But as always we stress to anyone who sees a koala drinking water on the ground and not returning to the trees, to contact your local koala rescue organisation for advice.
How can you help our koalas?
Did you know that you have the power to make a real difference in the lives of some of Australia's most beloved creatures? Our organization is passionately dedicated to providing free veterinary care for koalas.
Your generous support doesn't just help us keep our doors open; it becomes a lifeline for these precious creatures, enabling us to continue to offer vital medical aid to koalas, and indeed all wildlife, in desperate need. When you donate to our cause, you're not just giving money, you're giving a koala another chance at life, another day in the trees, another eucalyptus leaf to munch on.
Make a difference today - by supporting us, you become an invaluable part of the rescue efforts, directly contributing to the well-being of koalas in urgent need of veterinary care. Thank you for considering to stand with us in this crucial mission. Together, we can ensure a brighter future for these adorable animals!
Did you know that you have the power to make a real difference in the lives of some of Australia's most beloved creatures? Our organization is passionately dedicated to providing free veterinary care for koalas.
Your generous support doesn't just help us keep our doors open; it becomes a lifeline for these precious creatures, enabling us to continue to offer vital medical aid to koalas, and indeed all wildlife, in desperate need. When you donate to our cause, you're not just giving money, you're giving a koala another chance at life, another day in the trees, another eucalyptus leaf to munch on.
Make a difference today - by supporting us, you become an invaluable part of the rescue efforts, directly contributing to the well-being of koalas in urgent need of veterinary care. Thank you for considering to stand with us in this crucial mission. Together, we can ensure a brighter future for these adorable animals!
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References:
Cork, S. J., & Sanson, G. D. (1990). Digestive adaptations of the koala. Australian Natural History, 23(7), 498-503.
Ellis, W. A., & Bercovitch, F. B. (2011). Body size, reproductive phenology and life history in Koalas. Journal of Mammalogy, 92(1), 102-112.
Ellis, W. A., Melzer, A., & Carrick, F. N. (2002). Breeding dynamics of koalas in open woodlands. Wildlife Research, 29(1), 19-25.
Foley, W. J., Iason, G. R., & McArthur, C. (1999). Role of plant secondary metabolites in the diet of the koala. In: Nutrition for the 21st Century (pp. 45-58). Federation of Asian and Oceanian Biochemists and Molecular Biologists (FAOBMB).
Gillett, A., & Hanger, J. (2019). 32 Koala. Current Therapy in Medicine of Australian Mammals, 463.
Lawler, I. R., Stapley, J., Foley, W. J., & Eschler, B. M. (1998). Ecological example of conditioned flavor aversion in plant–herbivore interactions: effect of terpenes of Eucalyptus leaves on feeding by common ringtail and brushtail possums. Journal of Chemical Ecology, 24(1), 1-9.
Lunney, D., Crowther, M. S., Wallis, I., Foley, W. J., & Lemon, J. (2012). Koalas and climate change: a case study on the Liverpool Plains, north-west New South Wales. In Wildlife and Climate Change: Towards Robust Conservation Strategies for Australian Fauna, 150.
Marsh, K. J., Wallis, I. R., & Foley, W. J. (2003). The effect of inactivating tannins on the intake of Eucalyptus foliage by a specialist Eucalyptus folivore (Pseudocheirus peregrinus) and a generalist herbivore (Trichosurus vulpecula). Australian Journal of Zoology, 51(1), 31-42.
Moore, B. D., Wallis, I. R., Marsh, K. J., & Foley, W. J. (2004). The role of nutrition in the conservation of the marsupial folivores of eucalypt forests. In Conservation of Australia’s forest fauna (pp. 549-575). Royal Zoological Society of New South Wales.
Moore, B. D., & Foley, W. J. (2005). Tree use by koalas in a chemically complex landscape. Nature, 435(7041), 488-490.
Osawa, R. (1990). Formation of a clear zone on tannin-treated nutrient agar by a Streptococcus sp. isolated from feces of koalas. Applied and Environmental Microbiology, 56(3), 829-831
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Phillips, S., & Hopkins, M. (2007). Tweed Coast Koala Habitat Studyhttps://www.tweed.nsw.gov.au/files/assets/public/documents/environment/native-plants-and-wildlife/koala-habitat-study.pdf
Understanding koala life - Department for Environment and Water
Source: Strahan, Ronald (Ed) (1998) Complete Book of Australian Mammals, Australian Museum. Koala scent gland
https://cdn.environment.sa.gov.au/environment/docs/pa-fact-koalalife.pdf
Ellis, W., Melzer, A., Carrick, F., & Hasegawa, M. (2010). Tree use, diet and home range of the koala (Phascolarctos cinereus) at Blair Athol, central Queensland. Wildlife Research, 29(3), 303–311v
Mella, V. S. A., Ward, S. J., & McArthur, C. (2019). Needing a drink: Rainfall and temperature drive the use of free water by a threatened arboreal folivore. PLOS ONE, 14(5), e0216964.
Mella, V. S. A., Orr, C., & Hall, L. S. (2020). An insight into natural koala drinking behaviour. Ethology, 126(8), 858–863.
