Koalas: Australia’s Pickiest Eaters

Koalas, one of nature’s pickiest eaters, choose to only dine on eucalyptus leaves. (Photo credit: Purestock/Getty Images)

Many people have favorite foods. But the koala takes favorite food to the extreme. These Australian marsupials have evolved to live almost exclusively on eucalyptus leaves. And if that isn’t picky enough, recent research suggests that koalas are highly selective as to the species of eucalyptus they prefer and even the individual trees from which they choose to eat. How have these animals become so picky, and how can scientists use this information to aid in koala conservation efforts?

Filling a Niche

In ecological terms, the highly-selective diet of the koala makes them a specialist, that is, a consumer that primarily eats one specific organism or a very small number of organisms. Specialist species are generally sensitive to environmental changes, especially changes that affect the availability of their food source. However, the pickiness of koalas is likely an evolutionary adaptation.

Eucalyptus trees are the dominant trees of Australia. In fact, there are more than 700 species in the genus Eucalyptus, and most are native to Australia. However, the leaves of these trees are actually very low in protein, not easily digested, and contain compounds that are toxic to most species. Therefore, the ability for koalas to specialize in eating eucalyptus leaves has allowed them to fill an ecological niche. Koalas have virtually no competition for their preferred food source.

Koalas spend approximately 18-20 hours each day sleeping, and most of the remaining time is spent eating. They eat about 500 grams of eucalyptus leaves each day. A number of adaptations allow koalas to digest this food efficiently:

  • Powerful jaws allow the koala to chew the leaves into a very fine paste.
  • The koalas liver is able to deactivate the toxic compounds found in eucalyptus leaves.
  • A portion of the koalas large intestine is greatly enlarged to maximize the amount of nutrients extracted.

Studying Feeding Preference

Recent research has focused on finding what characteristics of eucalyptus leaves make them tasty for koalas. In one study, scientists tested a variety of leaves on captive koalas and recorded how much they ate. By analyzing the chemical composition of the leaves that koalas preferred, these scientists found that koalas ate less when the leaves provided to them were high in certain chemicals called formylated phloroglucinol compounds, or FPCs.

The next step in this study was to track wild koalas in a eucalyptus woodland. The scientists found that they were able to use the taste preferences of the captive koalas, based on chemical composition, to predict the tree preference of wild koalas. In addition, the scientists found that koalas spent more time in larger trees that were surrounded either by smaller, less-tasty trees or by larger trees that were equally tasty. Using this combination of leaf chemistry, tree size, and spatial environmental data, scientists hope to map koala habitats based on habitat quality, as a koala would see it.

Scientists hope that research on koala habitat quality will provide useful insight for future conservation projects for the species. (Photo credit: Joseph Van Os/The Image Bank/Getty Images)

The Future of Koala Habitats

All of this koala habitat mapping may prove very useful as the concentration of carbon dioxide continues to increase in the atmosphere. Other laboratory studies have shown that increases in carbon dioxide cause the concentration of toxins or compounds that otherwise interfere with digestion in eucalyptus leaves to increase. By studying how increased concentrations of carbon dioxide would affect the chemical composition of various Eucalyptus species, scientists may be able to predict which areas contain habitat that would most likely be of high quality for koalas in the future, and work to protect these areas.

More to Explore

While the BioZine is on summer vacation, enjoy this article from the archives. It was originally published in January 2011.


  1. This article made me wonder how koalas would adapt to being placed in an entirely different environment with no Eucalyptus trees to feed on.

  2. In my opinion, there are several reasons the koala prefers eucalyptus leaves. One factor could be purely based on taste preference. Perhaps when given the leaves high in FPC, the chemicals did not taste as good as eucalyptus leaves. Since there are no other animals competing for the same food source, there should not be a problem with koala conservation. Even though these leaves are low in protein, the koala has intestines to maximize the nutrients taken from eucalyptus leaves. The abundance of the trees with the preferred leaves, has more than likely caused the koalas to learn to adapt to them and use them as the number one source of food.

  3. That is so funny how an animal that sleeps practically all day long, eats Eucalyptus leaves that do not have any value in nutrition, and have toxic compounds. They aren’t even fat animals. How is this possible?

  4. koala seems more pickier than humans with there food. there food has to be the perfect thing.

  5. it so cute! 🙂

  6. Nathan Hall says

    I never knew that Koalas were so picky. The scientists who study this must have had to take a while just to find the right eucalyptus leaves.

  7. I never knew that Koalas only ate eucalyptus leaves. I just thougt that was their favorite. Also considering that all they basically do is eat and sleep, it’s a wonder that their not fat.

  8. Julie Hubbell says

    It seems that koalas may just be the pickiest marsupials. I think testing and experimenting on the growth of Eucalyptus trees would be the most beneficial in keeping the koala population steady. Surely if they can grow potatoes above ground and pumpkins that weigh 1,000 lbs., then they can create a Eucalyptus tree that is heartier and can balance the chemicals.

  9. i think it would be interesting to see what would happen if the eucalyptus plant died out or nearly did. would koalas just start to die or would they adapt and eat something else?

  10. Hannah Norman says

    i deffinately did not know that Koalas were such picky eaters. I could not just eat one leaf my whole like. It’s crazy how they sleep 18-20 days but I wouldnt mind doing that sometimes. haha. It the leaf does not have enough nutricios how do the Koalas servive?

  11. Evan Mitchell says

    If theoretically the Eucalyptus species slowly became endangered, would koalas become endangered along with it? Or would the koalas adapt to another food source in the same way they did Eucalyptus?

  12. Joey Alarid says

    I’m wondering why koalas are so picky about what they eat. We think humans are picky with what we eat but really we eat a wide range of foods. Its crazy how koalas can find the perfect tree to get food from.

  13. I had no idea koalas only ate one thing, i would think the same thing would get boring after eating them your whole life, but they must be pretty good. I’ll have to try some 🙂 Also, it makes me wonder what would happen if the eucalyptus trees all of a sudden got a disease or something.. if the koalas would starve, or find something else.

  14. Sarah Langford says

    I wonder what the koala’s would eat if there were no eucalyptus leaves.

  15. It’s insane that koalas only eat eucalyptus leaves, but it’s even MORE insane that they eat only certain kinds of eucalyptus leaves. They are not skinny animals, so I don’t understand how they stay so big while only eating the eucalyptus leaves.

  16. They r eventually going to have to find a new source of food since it will run out

  17. It’s strange to think that if the koala population had to be relocated even if just 100 miles for conservation reasons it would endanger most If not all of the koala population

  18. Intresting….It proves how important every organism is to the entire ecosystem, even the ones that seem not important.

  19. Tommmmmmmy says

    The article was okay. It wasn’t very interesting to me but I can see the importance of protecting areas for the bears.

  20. IlikeChicken says

    i wanna hug a koala bear some day… 🙂 they are very cute 😀

  21. This is very interesting. I didn’t realize how smart and precise koala bears were.

  22. I hope that koalas never become an endangered species because of human pollution or other ecological damages caused by humans.

  23. Man Koalas are so much fun.

  24. PPSIMMONS says

    These animals eat a food that grinds down their teeth which then causes them to eventually starve to death. Stupid evolution.

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