theory.]]> observed 130 koalas without collars.]]> species probably use tree trunks to cool down.]]> explained why koalas stayed on the trunk in the summer and higher up in winter.]]> extreme.]]> includes monkeys, leopards, birds and insects.]]> position and checked whether they liked high or low branches.]]> prefer different parts in different seasons?]]> probably aren't the only animals that know it.]]> tracked the koalas during the winter and summer.]]>