Koalas Keep Cool by Hugging Trees

Australia's native marsupial, the koala, loves to hug a nice tree trunk, particularly during a heat wave. According to ecophysiologist, professor Andrew Krockenberger of James Cook University in Townsville, much of this behavior has to do with a cooling process that helps the creature determine the amount of water they need to drink during high temperatures.

"If you save 50 per cent of the water you might have had to use, you then don't have dehydrating effects of a heatwave," says Krockenberger, via a press release. "For a koala this is not trivial."

As koalas can spend up to 20 hours a day sleeping, sometimes hanging onto the trunks of a tree, many may mistake the animal's sluggish behavior for laziness. However, this is certainly not the case. During hot weather, when the animal's body is slumped against the branches of a tree, pressing the front of its body against the bark, it is simply to help keep cool.

"Usually people look at that and think the koala's tired or 'stoned', but that's really not at all what's happening here," Krockenberger says. "This is a koala that is putting itself in a position which minimises the water that it has to evaporate."

Koalas wear an inch-thick insulating fur coat that helps keep them warm and prevents them from losing heat. However, their front fur is typically thinner, which is also the side exposed to the tree. Researchers predicted in a recent experiment that koalas cooled themselves by exposing their fronts with the less-insulated areas.

However, they found that tree trunks and branches hugged by koalas were typically cooler than the surrounding air by as much as 5 degrees Celsius.

In fact, researchers found that by lying on their fronts on a cool tree, koalas can transfer heat out of their body to the tree.

As heat waves may increase in the future with climate change, the findings stress the importance of trees for the survival of the animals. 

"In this particular case the coolest of the trees was an acacia, which is not a food tree."

More information regarding the findings can be seen via the journal Biology Letters.