Koalas are often photographed hugging trees -- even artwork frequently portrays them in this iconic pose. While it might look like they're just lazing about, scientists recently found there's a reason these marsupials are such tree huggers.
It turns out, they're trying to keep cool.
Scientists were somewhat confused when they observed koalas spending time hanging onto acacia trees when they exclusively eat the leaves of eucalyptus. It would seem inefficient to keep switching back and forth between trees.
“We were puzzled why they’d spend time and energy swapping trees when they were so clearly hot and exhausted,” zoologist Michael Kearney of the University of Melbourne told Science Magazine.
Speculating that the koalas might be seeking some relief from the heat, finding spots with more shade or a breeze, the scientists gathered weather metrics from different trees, including those that koalas weren't seen hugging, and found the species most used by these animals, aside from eucalyptus varieties, was the acacia.
They observed that the koalas only spent about 5 percent of their time in these trees on cooler days but up to 30 percent of their time on days when the temperature was more than 95 degrees Fahrenheit. The acacia tree trunks measured several degrees cooler than the air temperature and were even cooler than eucalyptus tree trunks.
"Using a biophysical model of heat exchange, we show that this behaviour greatly reduces the amount of heat that must be lost via evaporative cooling, potentially increasing koala survival during extreme heat events," the authors wrote in the study published in Biology Letters. "While it has long been known that internal temperatures of trees differ from ambient air temperatures, the relevance of this for arboreal and semi-arboreal mammals has not previously been explored. Our results highlight the important role of tree trunks as above ground ‘heat sinks,' providing cool local microenvironments not only for koalas, but also for all tree-dwelling species."
Kearney explained that the research showed "how even warm-blooded animals can be dependent on their environment for temperature regulation."
“This shows the many tricks that animals have up their sleeve to survive in harsh environments,” Kearney told Science Magazine.
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