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Thermal imaging has revealed koalas cope with extreme heat by resting against cooler tree trunks.

University of Melbourne researchers observed the behaviour of 30 Koalas during hot weather at French Island, to the city's east. They found that while panting and licking their fur helps koalas cool down, this can also lead to dehydration.

Lead researcher Natalie Briscoe, from the University's School of Botany, said koalas were observed hugging cool tree trunks.

“We found trunks of some tree species can be over 5°C cooler than the air during hot weather," she 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."

Researchers used a portable weather station on a long pole to measure what the koalas were experiencing in the places they chose to sit compared to the places available to them.

Researchers Natalie Briscoe and Andrew Krockenberger.Co-author Dr Michael Kearney said "the findings were important as climate change is bringing about more extreme weather".

“When we took the heat imagery it dramatically confirmed our idea that 'tree hugging' was an important cooling behaviour in extreme heat"

“Cool tree trunks are likely to be an important microhabitat during hot weather for other tree dwelling species including primates, leopards, birds and invertebrates.

"The availability of cooler trees should be considered when assessing habitat suitability under current and future climate scenarios.”

Study collaborator Professor Andrew Krockenberger, from James Cook University, said "heat wave events can hit koala populations hard".

"About a quarter of the koalas in one population died during a heat-wave of 2009, so understanding the types of factors that can make some populations more resilient is important.”

The study is published in the current edition of Biology Letters.