Koalas Hug Trees in Hot Weather

Bears cling to trunks during heat waves

No, koalas don't get more sympathetic as the heat turns up—tree-hugging is purely a survival tactic. (RobertDowner/ThinkStock)
Photo: RobertDowner/ThinkStock No, koalas don't get more sympathetic as the heat turns up—tree-hugging is purely a survival tactic.

Natalie Briscoe, a member of a University of Melbourne team studying the effects of climate change on Australian animals, was investigating how koalas regulate their body temperatures when she noticed an interesting seasonal shift in behavior.

During cool winters, koalas stuck close to palatable leaves in trees' highest branches. But as temperatures rose, koalas shimmied downward, "flopping" themselves over lower segments of tree trunks and clutching them more tightly.

"It looked like they were spread-eagled and uncomfortable," U of M professor Michael Kearney told the BBC. "It seemed like the wrong thing to do."

Upon further investigation, Briscoe and her partners realized that koala survival stems from their awkward warm-weather siesta positions.

Although Australian summer temperatures can be more than 100 degrees, researchers discovered that koalas' favorite tree hangouts were as much as seven degrees cooler than the daily high. The animals use trees as heat sinks, and thick trunks are the coolest parts of trees. Thermal imaging of koalas clutching trees on hot days confirmed suspicions.

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

As global temperatures increase, researchers say, animals like flying foxes and koalas will depend even more heavily on the cooling properties of tree microclimates.

Rising temperatures have probably forced you to look for loopholes to cool off. Unlike koalas, though, humans don't have to show trees extra affection to ward off heatstroke. If tree hugging isn't your favorite way to avoid overheating, consider taking cool trips in the summer months or dressing for the occasion.

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