Melbourne University researchers have found the reasons behind koalas' tree-hugging behaviour. The marsupial of Australia rests against cooler tree trunks to prevent its body from overheating during long periods of summer.
The life expectancy of a healthy koala is 16 years. Millions of koalas were hunted heavily for their fur in the early 1900s. Last year, the Australian government listed the marsupial in Queensland, New South Wales, and the Australian Capital Territory as a threatened species. Koalas could face extinction if effective protective measures are not implemented.
For the study, the researchers observed the behaviour of 30 koalas during hot weather at a French Island. They used radio collars to track the marsupial's movements and thermal imaging to gauge the tree trunk temperatures.
The researchers found that during summer koalas wrap their bodies around cooler, lower parts of the tree trunks - where the temperatures are estimated to be up to 9°C below air temperature (with the bark being particularly cool).
While panting and licking their fur helps them cool down, researchers said that it can also lead to dehydration. Hugging tree trunks allows the marsupial to transfer heat without the risk of dehydration. The cooling behaviour lowers the risk of heat stress in the tree-loving animals.
Researcher Natalie Briscoe said that the trunks of some tree species can be over 5°C cooler than the air during summer.
"Access to these trees can save about half the water a koala would need to keep cool on a hot day. Our results highlight the important role of tree trunks as above ground 'heat sinks', providing cool microenvironments not only for koalas, but also for all tree dwelling species," Briscoe said in a statement.
Co-author Dr Michael Kearney said that the findings are significant as climate change is causing extreme weather conditions. The accessibility of cooler trees should be considered while assessing habitat suitability under current and future climate scenarios.
Co-researcher Andrew Krockenberger said that heat wave can prove to be dangerous to koala populations.
"About a quarter of koalas in one population died during a heat wave in 2009, so understanding the types of factors that can make some populations more resilient is important," Co-researcher Andrew Krockenberger said.
The researchers said that other tree-dwelling species including primates, leopards, birds and invertebrates are also believed to be using a similar strategy to escape the scorching heat.
The finding is published in the Royal Society journal Biology Letters.
