Humans admire peacocks for their stunning tail feathers, but until recently no one could say whether the display actually drew the eyes of peahens. Now scientists, strapping cameras onto the heads of the female birds, have obtained evidence of what it is about peacock tails that attracts the opposite sex.

The peacock's tail, or train, was a riddle that vexed Charles Darwin as he sought to devise his theory of evolution: The principle of natural selection suggested that a species would develop traits that enhanced its chances of survival, but the extravagantly outsize train seemed more like a burden than an aid.

"The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!" the puzzled scientist wrote in 1860.