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| credit: Steve Griffiths |
We know why the chicken crossed the road, but why does the Koala hug a tree when it's hot? The
Guardian Australia tells us that because Koalas do not have sweat glands and have a thick fur coat, they hug cooler trees for relief. Some large trees can be up to 9℃ cooler than ambient temperatures. In heat waves becoming more frequent and longer as climate changes that is an important temperature difference. Biologists from the University of Melbourne directed their thermal imaging cameras at Koalas sprawled out on lower limbs of large trees during high temperatures on French Island. This position is not their usual behavior. The infrared imaging
[photo] shows the reason for their listless lounging: they are trying to keep cool. Koala stomach fur is thinner than the fur on their backs, so pushing it against a cool surface allows them to loose body heat without loosing scarce water. The wattle tree appears to be the coolest of the dominant tree species studied. Koalas only feed in gum (eucalyptus) trees, so moving to a wattle in a heat wave must be because of the tree's cooler surfaces. Wattles draw up cold ground water making the tree a natural air conditioner. But it can get too hot in parts of Australia even for this newly understood behavior to help. Hot climates act as a restraint on koala distribution.
