To start with, when the level of cineole was low, possums preferred the first enclosure.

ECONOMIST: Ecology raids the techniques of chemistry

But as the drip of the titration went up, from 0% to 1% to 2% to 5% and ultimately to 10% of the food being cineole, their behaviour changed.

ECONOMIST: Ecology raids the techniques of chemistry

When the food was toxin-free, the possums spent an average of 40 minutes of every hour eating safely under treelike cover and only 20 minutes in the risky, ground-like enclosure, and that scarcely changed for 1% and 2% cineole.

ECONOMIST: Ecology raids the techniques of chemistry

The switch began at 5%, and by the time the cineole level had reached 10% the ratio of time the animals spent in the two enclosures had reversed itself presumably reflecting, though this remains to be tested, the point at which they change trees in the wild.

ECONOMIST: Ecology raids the techniques of chemistry