In a study published in the Royal Society journal Biology Letters, scientists used thermal cameras to reveal that, in hotter weather, the animals moved to the lower, cooler parts of the trees.

 

They also pressed their bodies even closer to the trunks. 

 

The team, led by researchers from the University of Melbourne, was studying how koalas regulated their temperature.

 

This is part of a wider research project investigating the effect of climate on land-dwelling animals in Australia, a country which experienced an extreme heat wave earlier this year.

 

While PhD student Natalie Briscoe was studying the koalas' behaviour, she noticed that in the winter the animals would stay high in the trees - up near the leaves feeding. 

 

In the hotter summer weather though, they would move down.

 

Dr Michael Kearney from the University of Melbourne explained: "They'd just flop² over the [lower] tree trunks. 

 

"It looked like they were spread-eagled and uncomfortable; it seemed like the wrong thing to do." 

 

But measurements of the temperatures of the tree trunks showed that, on days as hot as 39C, they were up to seven degrees cooler than the air.

 

"That's what made us wonder if the koalas were using the trees as a heat sink," said Dr Kearney. 

 

The team used a thermal camera to take pictures of koalas on a particularly hot day. 

 

"When we got the images, back it was so obvious what the koala was doing," explained Dr Kearney. "You could see the koala sitting on the coolest part of the tree trunk with its bottom wedged right into the coolest spot.

 

"If we had thermal vision, it would have been an obvious thing."

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