THESE MARSUPIALS RELY ON EUCALYPTUS TREES FOR EVERYTHING: SHELTER, food, and water, even though the leaves are mildly toxic. Unfortunately, an increase in carbon dioxide in the atmosphere is changing the basic chemistry of eucalyptus leaves, leaving them less nutritious and more poisonous. To make matters worse, rampant droughts across Australia dry out foliage, meaning less moisture for koalas. In parched areas, the creatures can die of kidney failure brought on by dehydration. Some of these animals are now drinking from watering stations set up by researchers. Until recently, it was thought to be incredibly rare for koalas to actually sip liquid.