The primary diet of a koala bear consists mainly of eucalyptus leaves. Koalas are specially adapted to digest these leaves, which are toxic to most animals due to high levels of chemicals called phenolics. Despite the leaves being low in nutrients and calories, koalas can consume large quantities to meet their dietary needs. They spend a significant portion of their time resting in trees, as they conserve energy due to the leaves' poor nutritional value. The specificity of their diet makes them vulnerable to habitat loss, as they depend entirely on eucalyptus forests for survival.