When you think of “tree-huggers,” you don’t think cool. You instead probably imagine ponchos, Birkenstock sandals and controlled substances. Not so when it comes to koalas, according to research out of the University of Melbourne: They hug trees for a (literally) cooler reason – it helps them survive Australia’s sometimes brutal temperatures.

In extremely hot weather, koalas use tree trunks and limbs as heat sinks to help draw off potentially deadly body heat. Lead researcher Natalie Briscoe and her team observed the behavior of 30 Koalas with thermal imaging equipment during hot weather at French Island. Though panting and licking their fur also helps, this leads to dehydration, as it requires the animals to give up precious moisture.

“We found trunks of some tree species can be over 5°C cooler than the air during hot weather,” Briscoe said. “Access to these trees can save about half the water a koala would need to keep cool on a hot day. This significantly reduces the amount of heat stress for koalas.”

As climate change brings with it more extreme weather, things like tree trunks may become essential “microhabitats” for animals not yet accustomed to the wild temperature swings. Understanding this is important in the conservation of animals like koalas, who can be particularly susceptible to heat. About 25% of the koala population was lost in a 2009 heatwave, researchers say.

“The availability of cooler trees should be considered when assessing habitat suitability under current and future climate scenarios,” said co-author Dr Michael Kearney.

Photo credit: S.Griffiths