Why Do Koalas Sleep So Much? Eucalyptus and Energy Explained

How long do koalas sleep?

Most sources give a figure of about 18–20 hours of sleep a day, and up to about 22 hours when quiet resting is included. The exact amount changes with the season, the temperature and the individual. A koala is usually awake for only a few hours, mostly at night and around dusk, and spends that time feeding in several short sessions.

Koalas sleep in trees, usually wedged into the fork of two branches, curled into a ball in cold weather or sprawled along a branch in the heat. They often stay in the same tree for a day or more, eating and sleeping in it. They come down to the ground only to move to a new tree, and those trips usually take just a few minutes a night.

A low-energy diet

The main reason for all this rest is food. Eucalyptus leaves are among the poorest foods any mammal eats:

• Low in energy and protein. The leaves have little sugar, starch or fat and not much protein.
• High in fiber. Much of each leaf is tough, woody material that is hard to break down.
• Full of toxins. Eucalyptus oils and other chemicals are poisonous to most mammals, and the koala’s liver must spend energy neutralizing them.

To get anything out of this food, koalas chew it very finely with grinding cheek teeth and then ferment it slowly in a huge caecum, a side pouch of the gut that can reach about 2 m (6.6 ft) long. Leaves may take several days to pass through the gut.

The result is a tight energy budget. Koalas have a metabolic rate roughly half that of a typical placental mammal of similar size. Even their brains are small for their body size, possibly because brain tissue is expensive to run. Sleeping and sitting still for most of the day is the simplest way to spend as little energy as possible. Learn more about their menu in what do koalas eat?

Myth: are koalas drugged by eucalyptus?

A popular story says that koalas are “stoned” or “drunk” on eucalyptus oils. There is no evidence for this. The compounds in the leaves are not sedatives for koalas: their liver enzymes break them down, and their gut microbes help them cope with the fiber.

The sleepiness is the result of the poor nutrition, not of any drug-like effect. Animals with other low-energy diets, such as tree sloths, show a similar slow, energy-saving lifestyle. Interestingly, sloths sleep far less than their reputation suggests; see how long do sloths sleep?

How koalas keep cool while resting

Resting in the open on hot Australian days is risky for a furry animal. Koalas do not sweat much, and panting or licking their forearms costs precious water. Instead, they change where they sit.

In 2014 a team of Australian researchers used heat-sensing cameras to watch koalas during hot weather. They found that the animals moved down to the lower trunk and lower branches and pressed their bellies and limbs against the bark. The tree trunks were several degrees cooler than the surrounding air, so this “tree hugging” let koalas lose body heat without losing water.

On cold or wet days koalas do the opposite, curling up tightly with their backs to the wind so that their thick, water-shedding back fur protects them.

Do koalas sleep more than other animals?

Koalas are among the sleepiest mammals, though exact comparisons are tricky because sleep is measured in different ways. Some bats, such as the little brown bat, are also known to sleep about 20 hours a day. Large plant-eaters like elephants and giraffes sleep only a few hours a day, because they must spend most of their time feeding to fuel their huge bodies. The koala takes the opposite approach: instead of eating more, it does less, and saves energy by staying still.

Is a sleepy koala a healthy koala?

Long hours of rest are normal for koalas, and a koala dozing in a tree is behaving exactly as it should. In the wild, however, koalas that sit on the ground for long periods, look weak or have crusty eyes may be sick or injured, often from heat stress, disease or dog attacks.

If you see a koala that seems in trouble in Australia, do not touch it. Keep pets away and contact a local wildlife rescue group or the state wildlife authority.