Koalas are often pictured in trees, hugging on to limbs or trunk of a tree. Many times, these animals hug trees tightly, with their heads tucked to one side. Now, researchers believe they know why the marsupials exhibit this behavior.
A koala's diet consists mostly of eucalyptus leaves. But, the distinctive tree-hugging behavior is not a feeding mechanism, according to researchers.
University of Melbourne investigators believe the marsupials hug trees in order to cool down in high temperatures.
The study photographed koalas in infrared light, examining how heat is transferred as the animals rested and grasped trees. A total of 30 koalas on French Island, east of Melbourne, were recorded during hot weather.
Panting and licking fur can help koalas stay cool in high temperatures, but these actions also drain the marsupials of water. This can lead to dehydration, a potentially dangerous situation under those conditions.
"We found trunks of some tree species can be over 5°C cooler than the air during hot weather," head researcher Natalie Briscoe, from the University of Melbourne's school of botany, said.
By hugging tree trunks, koalas are able to stay cool without losing water.
"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," Briscoe stated in a university press release.
During the study, a large wattle tree was the coolest of all the trees in the forest. This was also a popular resting spot for the marsupials. Since koalas do not eat leaves of the wattle tree, researchers believe the animals rested in the trees primarily as a means of lowering their body temperatures.
"[T]his behaviour greatly reduces the amount of heat that must be lost via evaporative cooling, potentially increasing koala survival during extreme heat events," researchers wrote in a paper announcing their study.
Researchers are not sure why the trees are cooler than the surrounding air. The reason may simply be water transporting through the limbs to bring moisture to leaves.
If the conclusions of the researchers are correct, then other animals, including primates, birds and some large cats, may also use trees as a heat sink, cooling their bodies. A separate study, conducted by University of Sydney researchers, found koalas seek out trees in cool, low-lying areas in hot weather.
Koalas are dependent on eucalyptus leaves as a food source, and researchers say human activities are threatening those trees.
Investigation of the use of trees for cooling by koalas was published in the journal Biology Letters.
