What Do Koalas Eat? Eucalyptus Leaves and Fussy Diets

Which eucalyptus do koalas eat?

Eucalyptus trees, also called gum trees, dominate many Australian forests, and more than 600 species are known. The koala is not equally keen on all of them. Across its range it regularly eats only a few dozen species, and each local population focuses on the species that grow best in its area.

Some of the most important food trees include:

• Tallowwood (Eucalyptus microcorys) in coastal Queensland and northern New South Wales.
• Forest red gum (Eucalyptus tereticornis) along much of the east coast.
• River red gum (Eucalyptus camaldulensis) along inland rivers and creeks.
• Manna gum (Eucalyptus viminalis) in Victoria and South Australia.

Wild koalas also spend time in, and sometimes nibble, other native trees such as wattles (Acacia), paperbarks (Melaleuca), she-oaks (Allocasuarina) and cypress pines (Callitris). They may use these trees for shade or shelter as much as for food.

Why are koalas such fussy eaters?

Koalas pick their leaves carefully, and they have good reasons. Even within one eucalyptus species, leaves from neighboring trees can differ greatly in how much protein and how many toxic compounds they contain.

Researchers have found that koalas avoid leaves rich in certain defensive chemicals, especially a group called formylated phloroglucinol compounds, and prefer leaves with more nitrogen, a sign of protein. A koala sniffs a branch before eating it, which helps it judge the leaves by their smell. It may reject one tree and feed heavily from the tree next to it.

This selectivity is one reason why koalas need large areas of healthy forest. A patch of eucalyptus that looks fine to people may hold very few trees a koala can actually live on.

How do koalas digest toxic leaves?

Eucalyptus leaves are tough, low in energy and full of oils and other compounds that would poison most mammals. Koalas cope in several ways:

• Teeth. Sharp front teeth nip off leaves, and ridged cheek teeth grind them into a fine paste, which makes digestion more efficient. Koalas can store leaves briefly in their cheeks.
• Liver enzymes. Special liver enzymes, from a family called cytochrome P450, break down the toxic compounds so they can be removed from the body.
• A giant caecum. The caecum, a side pouch of the gut, can be up to about 2 m (6.6 ft) long, one of the largest relative to body size of any mammal. There, bacteria ferment fiber over a long time.
• Slow digestion. Food can stay in the gut for several days, so the koala extracts as much as it can.

Even with all these adaptations, the diet supplies little energy. That is why koalas sleep or rest for most of the day; see why do koalas sleep so much?

How much do koalas eat?

An adult koala eats roughly 200–400 g (7–14 oz) of leaves a day. Large males from the south eat more than small females from Queensland. The koala spreads its meals over about four to six feeding sessions, mostly at night and around dusk.

When feeding, the koala holds onto the branch with three limbs and pulls leafy twigs toward its mouth with the fourth. Lighter animals can move out toward the ends of branches, where the young leaves grow, while heavy males often feed closer to the trunk.

Do koalas drink water?

For a long time, people believed that koalas never drink, and a popular explanation says the name “koala” means “no water” in an Aboriginal language. In fact, koalas get most of the moisture they need from fresh leaves, which can be more than half water, so they drink only rarely in normal conditions.

Field studies have shown that wild koalas do drink, especially in hot, dry weather. They lick water running down tree trunks during rain, and they visit creeks, dams and puddles in heat waves and droughts. As climate change brings longer droughts, drier leaves become a real problem for koalas.

What do baby koalas eat?

A newborn joey lives on its mother’s milk for its first months in the pouch. Before it can digest leaves, it needs the right gut microbes. At about six months old, the joey begins to eat pap, a soft, runny form of its mother’s droppings produced from her caecum. The pap passes on the bacteria that help break down eucalyptus.

The joey then gradually adds young leaves to its diet while still drinking milk. It is fully weaned at around one year old.

Can koalas survive without eucalyptus?

No. Koalas are among the most specialized plant-eaters in the world, and they cannot live long on other food. This specialization is one of their biggest weaknesses: when land clearing, bushfires or drought remove their food trees, koalas cannot simply switch to another diet. Learn more about these threats in are koalas endangered?

The giant panda is a similar example from China: it lives almost entirely on bamboo, a food few other animals eat.