theory.]]> scarce.]]> determine how much heat a koala could lose by hugging a cool tree.]]> conducts heat.]]> observed 130 koalas that weren't wearing collars.]]> device recorded the temperature near where the koalas made themselves comfortable.]]> appealing in different seasons?]]> species of trees in the heat of summer.]]> exposed more of their surface area.]]> marsupials don't seek shelter.]]> Biology Letters.]]> excess heat on a 95-degree day by hugging a cool tree in a shady spot.]]>