Koala Cuisine Quandary

Why did the koala cross the road? To get to less harmful leaves of a tree on the other side, according to new Australian research.

For years koalas have baffled scientists by risking life and limb crossing busy highways to eat from a particular eucalyptus tree and snub hundreds of other trees of the same species.

"We identified this new chemical in those particular eucalyptus trees which stopped the koalas from eating them," said William Foley of the Australian National University.

An ANU study has revealed the levels of formyl phloroglucinol compounds (FPCs) played a large role in determining which eucalyptus leaves were palatable to koalas and which ones they avoided. Those trees with leaves that had higher levels FPC were virtually ignored by the animals.

Koalas have a digestive system that lets them metabolize poison in eucalyptus trees that could be toxic to humans, but FPCs damages the animal's small intestines and causes nausea.

One of the aromatic oils that gives eucalyptus its distinctive smell acts as a clue to the koalas indicating the presence and levels of FPCs.

Koalas are indigenous to Australia and in danger of extinction. They are also the animal kingdom's fussiest eaters. They are known to sift through 20 pounds of leaves a day to find the one pound they need to survive.

A koala's diet is almost wholly restricted to eucalyptus leaves, which are very low in energy-producing nutrients.

It is the picky eating habit and human encroachment that has the animal at risk. Since European settlement, about 80 percent of Australia's eucalyptus forests have been cleared and most remaining trees are on private land, putting a strain on the koala population.

The koala's slow movement also makes it a frequent victim of dogs, cars and bush fires. The Australian Koala Foundation says that 4,000 of the rare animals are killed each year by dogs and traffic.

Koalas now number less than 100,000 in the wild -- down from millions in the 1920s when they were killed for their fur.