Koalas: Leaf Connoisseurs

When it comes to picking out dinner, koalas have to take special care. Only certain leaves are good for the marsupials - others make them very sick.

"Fortunately for bushwalkers, the koalas' learned association between nauseating toxins and the smell of certain leaves means they don't become physically sick," said Ben Moore from the School of Botany and Zoology at the Australian National University in Canberra.

Brown and his colleagues mapped the contents of nutrients and toxins in every tree in an area of forest on Victoria's Phillip Island. They combined the map with 10 years of data collected by the local Friends of the Koalas group.

They found that koalas tend to prefer large trees - which provide more food and shelter and a better chance of interacting with other koalas - over smaller trees. However, among the large trees koalas stay away from the ones that have leaves that will make them sick or contain fewer nutrients.

"It's like having to choose between 1000 restaurants (or trees in the koalas' case), spread all over town, without a restaurant guide," Moore said. "This reinforces the need to conserve large old trees for all wildlife, not just those species that use hollows for nesting."

This research was published in the May 26 issue of the Journal Nature.