Scientists had long assumed that flamingo feathers change color only when the plumage becomes faded by the sun or unintentionally stained by organic materials.

But while studying greater flamingos at the Doñana Biological Research Station in Spain, ornithologist Juan Amat realized that something else was going on.

"We noticed that immediately after chicks were hatching, [adult] flamingos lost their pink color," he said. (See wading-bird pictures.)

Adults later regained their famous pink plumage, "yet they were not moulting, so we wondered if there was something cosmetic to consider."

To examine this hypothesis, the researchers studied seasonal variations in flamingo color at three wetlands in Spain. The team also monitored