A KOALA SPRAWLED on the trunk of a eucalyptus isn't just resting its paws; it's hugging the tree to stay cool in hot weather, according to researchers from the University of Melbourne. 
 
 "If we all had infrared vision, we'd have known all along what koalas are doing," says lead author of the study Dr Michael Kearney, senior lecturer in zoology at the University of Melbourne. 
 
 It was Michael's student, zoology postgraduate Natalie Briscoe who first stumbled across this phenomenon while measuring the microclimates of koala habitats in south-eastern Australia. 
 
 The team had a thermal-imaging camera on hand, and were surprised to discover that the tree trunks - the ones with koalas splayed across them - were on average more than 5°C cooler than the surrounding temperature. 
 
 Koalas hug trees for quick cooling 
 
 In hot weather animals and birds often avoid overheating via 'evaporative cooling'. Humans produce sweat, which evaporates and cools the skin in the process. 
 
 Animals that don't have sweat glands often pant like dogs or lick their fur to achieve the same effect. However, for tree-dwelling animals saliva is a luxury they can't spare. 
 
 "Koalas are stuck up on a tree. They pant and lick their fur, but that's emergency stuff," explains Michael. "They don't have much in the way of drinking water. So, if you're a koala, you want to minimise the amount of water you lose." 
 
 The researchers tracked 37 radio-tagged koalas and measured the temperatures surrounding them up in the canopy. After gathering data on tree trunk temperatures and calculating how much heat koalas need to shed, the team was able to determine that tree hugging could cool koalas down by as much as 68 per cent, thus reducing the need to evaporate precious water. 
 
 "What they've done is really neat," says Dr Bill Ellis, a wildlife researcher at the University of Queensland who didn't participate in the study. "This is something I've been thinking about for years." 
 
 Koalas seek non-food trees to cool down 
 
 The researchers measured four species of eucalyptus and one type of acacia. Notably, the acacia provided even more cool relief during heatwaves, which may explain why the marsupials hang out in a tree they don't actually eat from. But the scientists are not entirely sure why trees are so cool in the first place. 
 
 "My guess is that trees have thermal inertia, meaning they heat up and cool down more slowly than the ambient temperature," says Michael. "It might also have to do with the cool groundwater they pull up through their roots." 
 
 The findings may also hint at the reason why koalas are less prevalent in the north of Australia. "Previously we thought koala spread was either related to predators or humidity," says Bill. 
 
 "It changes the way we think about habitat requirements for koalas," Michael agrees. "But it might only work in places that are less hot." 
 
 With the warming climate koalas might be hugging more trees in the future, and more research will be needed in other areas of Australia. 
 
 "Where we study koalas, it gets up to 40 degrees," Bill points out. Hugging a tree in these conditions might not be efficient enough. 
 
 The study was published today in Biology Letters. ||||| Media playback is unsupported on your device Media caption Dr Michael Kearney from the University of Melbourne explains how the koalas hug trees to regulate their temperature 
 
 Hugging trees helps koalas to keep cool, a study has revealed. 
 
 In a study published in the Royal Society journal Biology Letters, scientists used thermal cameras to reveal that, in hotter weather, the animals moved to the lower, cooler parts of the trees. 
 
 They also pressed their bodies even closer to the trunks. 
 
 The team, led by researchers from the University of Melbourne, was studying how koalas regulated their temperature. 
 
 Image copyright S Griffiths Image caption Thermal images revealed how cool the trunks of large trees were 
 
 This is part of a wider research project investigating the effect of climate on land-dwelling animals in Australia, a country which experienced an extreme heat wave earlier this year. 
 
 If we had thermal vision, it would have been an obvious thing Dr Michael Kearney, University of Melbourne 
 
 While PhD student Natalie Briscoe was studying the koalas' behaviour, she noticed that in the winter the animals would stay high in the trees - up near the leaves feeding. 
 
 In the hotter summer weather though, they would move down. 
 
 Dr Michael Kearney from the University of Melbourne explained: "They'd just flop over the [lower] tree trunks. 
 
 "It looked like they were spread-eagled and uncomfortable; it seemed like the wrong thing to do." 
 
 But measurements of the temperatures of the tree trunks showed that, on days as hot as 39C, they were up to seven degrees cooler than the air. 
 
 Media playback is unsupported on your device Media caption See a male koala making the extraordinary bellowing sounds (footage by Benjamin D Charlton at Lone Pine Koala Sanctuary, Brisbane) 
 
 "That's what made us wonder if the koalas were using the trees as a heat sink," said Dr Kearney. 
 
 The team used a thermal camera to take pictures of koalas on a particularly hot day. 
 
 "When we got the images, back it was so obvious what the koala was doing," explained Dr Kearney. "You could see the koala sitting on the coolest part of the tree trunk with its bottom wedged right into the coolest spot. 
 
 "If we had thermal vision, it would have been an obvious thing." 
 
 Deadly heat 
 
 Dr Kearney said large trees had their own protective "microclimate", which is likely to become increasingly important to tree-dwelling creatures like koalas if global temperatures continue to increase as predicted. 
 
 Image copyright Justin Welbergen Image caption Thermal images of flying foxes reveals their response to heat stress 
 
 Another researcher who has used thermal cameras in his ecological research - Dr Justin Welbergen from James Cook University - says thermal images show exactly how animals can exploit these cooler microclimates in trees. 
 
 "This helps them to maximise their chances of survival during extreme heat events," He told BBC News. 
 
 Research Dr Welbergen published earlier this year revealed the effects on wildlife of such extreme events. His research revealed that 45,500 flying foxes had died on just one extremely hot day in southeast Queensland. 
 
 "Our thermal video shows group of flying-foxes trying to cope with an extreme heat event by distributing saliva on their wings," he explained. 
 
 Hugging trees, Dr Kearney said, helps the koalas to avoid similar water loss - enabling them to "dump heat" into the tree and to avoid panting. 
 
 Follow Victoria on Twitter ||||| The mention of a koala bear often conjures up an image of an adorable spoon-nosed creature cocking its head to one side while clinging to a tree. 
 
 Now, scientists have figured out why the iconic Australian marsupials hug trees: The trunks help the koala bears keep cool, according to a new study. 
 
 "It can be a really useful way of getting rid of heat on a hot day," said study co-author Michael Kearney, an ecologist at the University of Melbourne in Australia. 
 
 Tree huggers 
 
 Given that koalas spend so much time in trees — the marsupials live in Australia's woodlands where they munch on leaves and sleep — nobody wondered why they hugged the trunks. People just thought they were taking a break on a more stable spot after eating leaves in the branches, Kearney said. [Marsupial Gallery: A Pouchful of Cute] 
 
 As such, the discovery came as a surprise. Kearney and his student, doctoral candidate Natalie Briscoe, were trying to predict how the woodland creatures on French Island, near Melbourne, would regulate their body temperatures as the continent heats up due to climate change. The region is cool most of the year, but during the summer, the temperature routinely spikes above 104 degrees Fahrenheit (40 degrees Celsius), Kearney said. 
 
 Briscoe measured wind and shade levels using a portable weather station, but didn't find any striking trends. Then she pointed to an infrared thermometer, which measures temperature based on thermal radiation, at the tree trunks the koalas were hugging. The trunks were considerably cooler than the ambient air temperature — sometimes by as much as 9 degrees F (5 degrees C), Kearney said. 
 
 She also noticed the koalas clinging to acacia trees, even though they normally eat eucalyptus leaves. [See Images of the Tree-Hugging Koalas] 
 
 "As it got hotter the koalas went farther down the trees and started to really hug onto the tree trunks," Kearney told Live Science. "That seemed strange to us until we figured out that the trees are a bit cooler." 
 
 Stay cool 
 
 Koala bears pant to keep cool, letting evaporated moisture from their mouths carry heat away from their bodies. 
 
 When the team modeled koala bear heat transfer, they found the tree-dwellers save half the water they would have used panting if they hug trees instead. 
 
 Koalas get most of their water from their diet, but because eucalyptus leaves are laced with a toxin, the koalas can eat only a limited amount before the toxin harms the animals, Kearney said. 
 
 So tree-hugging could be critical to their survival on hot days, by allowing them to cool off without wasting precious water through panting, Kearney said. 
 
 It's not clear exactly why their preferred tree trunks are cool, but one possibility is that they pull in a lot of groundwater, which stays closer to the annual average air temperature, rather than the current air temperature, he said. 
 
 Climate change planning 
 
 Koalas' food (and hugging) trees will change their range with the hotter and drier weather brought by climate change, Bill Ellis, a wildlife researcher at the University of Queensland in Australia, who was not involved in the study, wrote in an email to Live Science. 
 
 But the new study suggests that food may be a smaller consideration in preserving koala habitat than previously thought, he said. 
 
 "As long as we plant trees koalas will eat, perhaps the other trees we plant just need to provide the right mix of shelter and heat sink characteristics," Ellis said. "It's quite an interesting concept, but non-native trees might be the future for koalas — as long as they also have the right fodder." 
 
 Farther north in the koala's range, the air is muggy and it feels hotter, so scientists should see how tree-hugging plays out in in different locations in the koala's habitat, Ellis said. 
 
 "Humidity means that the power of evaporation for cooling is reduced," Kearney said. So tree-hugging may be even more important up north, where evaporative cooling doesn't work as well, he said. 
 
 The study was published today (June 3) in the journal Biology Letters. 
 
 Follow Tia Ghose on Twitter and Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.
– Using thermal cameras, researchers in Australia uncovered the science behind a habit that seems, well, cute: Koala bears hug trees to cool themselves. It turns out that tree trunks can be up to 12 degrees cooler than the air, and with Australia's recent hot spells rising well above 100 degrees, koalas get extra huggy. Conversely, in the cold of winter, the marsupials tend to climb higher into trees, closer to the leaves they eat. The scientists came to their conclusion after using thermal cameras on a particularly hot day. "If we had thermal vision, it would have been an obvious thing," a University of Melbourne researcher tells the BBC. "You could see the koala sitting on the coolest part of the tree trunk with its bottom wedged right into the coolest spot." And in doing so, koalas manage to conserve a substantial amount of water: They typically cool themselves by panting, LiveScience explains, with heat escaping their bodies by way of the moisture leaving their mouths. Modeling showed tree hugging halved the amount of water that would otherwise be lost. The study also explains why the marsupials have been spotted in acacia trees, which aren't a food source: Those trunks get cooler than eucalyptus trunks, notes Australian Geographic. As for why the trees in general are cooler, researchers say it's possibly because they pull in nearby groundwater, whose temperature doesn't fluctuate as much as air temps do. (Earlier this year, Australia's heat caused thousands of dead bats to fall from the sky.)