Mention koalas and the image that comes to mind is that of a cuddly animal snoozing, whilst clinging on to a tree trunk for dear life - and rightfully so, given that the animals sleep for up to 20 hours a day! However, while the fact that their sedentary lifestyle is caused by their unusually small brains and the limited nutritional content of the eucalyptus leaves they consume is well-known, what was never questioned was their penchant for tree trunks. Turns out that the smart koalas have figured out that staying close to trees is the best way to beat the heat, during the hot Australian summers.