The smells may drive some species to extinction, unless conservationists take unorthodox measures, such as adding "deodorant" to bird nests, according to biologist Jim Briskie of Canterbury University in Christchurch, New Zealand.

Many bird scents stem from a gland that produces waxes essential to keeping feathers healthy.

In Europe and the Americas, birds' bodies alter this preening wax during breeding season, changing the wax's composition to reduce smells and keep the birds' nests less detectable by predators that use their noses to find food.

In a recent experiment in New Zealand, Briskie compared waxes from six native species, such as robins and warblers, with waxes from invasive species, such as blackbirds and sparrows, which had evolved in Europe until the 1870s.

"The European