Koalas don't hug trees because they love them. Trees keep koalas cool, scientists say.

On a hot day in Australia, a koala's thick fur makes it hard to stay cool. The over-heated koalas don't seek shelter and water can be hard to find. In the wild, many koalas die when the heat becomes extreme. This is according to a report published Wednesday.

The scientists guessed that koalas must do something to cool down in hot weather. So they put radio collars on 37 koalas in southeastern Australia. They tracked the koalas during the winter and summer. In Australia, summer lasts from December to March.

The researchers recorded what the koalas did. They noted their body position and checked whether they liked high or low branches. The scientists measured the air temperature a couple of feet from the koalas.

The scientists also observed 130 koalas without collars.

They discovered that koalas behaved differently on hot days than on cooler days. In the summer, the animals stretched out. A larger part of their bodies were in contact with the trees. They also often hugged a tree trunk or branch closer to the ground. In the winter, koalas climbed higher up the tree and farther out onto the branches.

I'll Take The Trunk, You Take The Branch

Why would koalas prefer different parts in different seasons? To answer that question, the scientists measured the temperatures of four kinds of trees. Three of the trees were eucalyptus trees. One was an acacia tree.

The trunks were cooler than the branches or tree tops. The trunks were also cooler than the air. This explained why koalas stayed on the trunk in the summer and higher up in winter.

Of all the trees tested, the coolest ones were the Acacia mearnsii trees. The koalas seemed to really like these trees. They spent nearly one-third of their time on them in summer. In the winter, though, they spent very little time on them. Koalas can't eat their leaves. But now scientists think they know why koalas like them so much.

Thick Fur Is Hot In The Summer

The scientists needed to check their theory. They figured out how much heat a koala loses by hugging a tree. They also figured out the thickness of a koala's fur and how much fur touches the tree. Scientists discovered that an adult koala loses most of its extra heat by hugging a cool tree. That could mean the difference between life and death.

Tree hugging is a clever way to chill out. And koalas probably aren't the only animals that know it.

Many tree-dwelling species probably use tree trunks to cool down. That includes monkeys, leopards, birds and insects.

The report will help people predict how animals will keep cool in a warming climate. It will help them choose the most important wild places to preserve.]]>