Greg Miller in Wired:
The peacock’s tail gave Darwin fits. At first, it seemed to fly in the face of his theory of natural selection. How could evolution possibly favor such cumbersome and conspicuous accoutrement? The very sight of those feathers, Darwin famously wrote to a colleague, made him sick. He soon realized, however, that the feathers might serve another purpose: enhancing the male’s reproductive success even as they made him more visible and vulnerable to predators. The concept of sexual selection was born, and the peacock’s tail remains a textbook example of it to this day.
But exactly what it is about the male’s display that females find attractive is far less clear.
Studies with feral peafowl at a British wildlife park in the 1990s suggested that it’s the ornamentation. Behavioral ecologist Marion Petrie of Newcastle University and her colleagues found that males with more eyespots mate more often. When the researchers used scissors to snip off 20 eyespots from several males, females showed less interest in them. Petrie’s work suggested that in the mind of a peahen, eyespots are pretty sexy.
If that’s true, she should spend a lot of time looking at them when the male does his display, says Michael Platt, a neuroscientist at Duke University and co-author of the new paper, published today in the Journal of Experimental Biology. Platt has previously used eye-tracking equipment to study primate behavior, including the social interactions of freely-moving lemurs, and in the new study he and colleagues developed an even smaller system that could fit on the head of a peahen.