Cool Tree Trunks Help Koala Bears Beat The Heat
June 4, 2014

Cool Tree Trunks Help Koala Bears Beat The Heat

Brett Smith for - Your Universe Online

Koalas can often be seen lazily wrapped around a tree branch on a hot summer’s day and a new report in the journal Biology Letters revealed that this behavior helps to cool the marsupials down.

Using thermal imaging technology, study researchers observed koalas hugging tree branches and trunks on French Island, situated just east of Melbourne, Australia. While the animals can pant and lick their fur to stay cool, these methods can lead to dehydration, the study team said.

“We found trunks of some tree species can be over [9 degrees F] cooler than the air during hot weather," said Natalie Briscoe, a zoology researcher at the University of Melbourne.

"Access to these trees can save about half the water a koala would need to keep cool on a hot day,” she added. “This significantly reduces the amount of heat stress for koalas."

For the study, researchers utilized a portable weather station to see what the koalas were experiencing in their selected resting places compared to other places available to them. The researchers discovered that in the winter the koalas would stay up high in the trees – while in the summer they would move lower down.

"They'd just flop over the (lower) tree trunks,” study author Michael Kearney, from the University of Queensland, told Victoria Gill of BBC News. "It looked like they were spread-eagled and uncomfortable; it seemed like the wrong thing to do."

However, thermal observations revealed a method to the koala’s madness.

"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.”

Kearney suggested that the koalas were taking advantage of a tiny microclimate and added that the study findings “were important as climate change is bringing about more extreme weather.”

“Cool tree trunks are likely to be an important microhabitat during hot weather for other tree dwelling species including primates, leopards, birds and invertebrates,” he said. "The availability of cooler trees should be considered when assessing habitat suitability under current and future climate scenarios.”

Study author 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,” he said.

Scientists focused on sustaining koala populations also look at the mating habits of these animals. A study published in December revealed that male koalas have a specialized organ in their throats that they use to make distinctive calls for prospective mates.

The study team speculated that koalas evolved this special organ as a way of showing off a male’s breeding quality. Bigger males are probably capable of producing deeper, louder bellows – giving them more attention than smaller males. This would give females a way to judge a male’s quality as a potential mate.