If a blue jay sees a normal-looking salamander, it will eat it. But if the same bird sees a freak, it may let it go.

University of Tennessee researcher Benjamin Fitzpatrick says this discovery, which his team reports in the open access journal BMC Ecology, suggests why rare traits persist in a population.

Predators detect common forms of prey more easily, the scientists figure. The majority that share a common look are always on the dinner menu, while oddballs are left to reproduce.

"Maintenance of variation is a classic paradox in evolution because both selection and drift tend to remove variation from populations," Fitzpatrick explained today. "If one form has an advantage, such as being harder to spot, it should replace all others. Likewise, random drift [genetic change that occurs by chance] alone will eventually result in loss of all but one form when there are no fitness differences. There must therefore be some advantage that allows unusual traits to persist."

The researchers placed a selection of food-bearing model salamanders into a field for six days, with striped models outnumbering the unstriped by nine to one, or vice versa. On test days, the numbers were evened out. In each case, Blue Jays were more likely to attack the models that had been most prevalent over the previous six-day period.

"We believe that the different color forms represent different ways of blending in on the forest floor," Fitzpatrick said. "Looking for something cryptic takes both concentration and practice. Predators concentrating on finding striped salamanders might not notice unstriped ones."