What makes an ideal man? For some women, it’s a charming personality; others just want to see a nice set of abs. Things aren’t quite so complicated in the rest of the animal kingdom. In most species, every female prizes the same trait in a male, whether it be bright plumage or a pretty song. So researchers have been surprised to discover that female yellowthroats don’t always agree on what turns them on–a finding that may offer a window onto speciation.
Male yellowthroats sport large black masks and bright yellow bibs. Vibrant colors result from pigments called carotenoids, which are also antioxidants and thus a sign of health. So it was little surprise when biologist Corey Freeman-Gallant of Skidmore College in Saratoga Springs, New York, and colleagues found in 2001 that local female yellowthroats preferred males with the most vivid yellow bibs. But in the same year, biologist Peter Dunn of the University of Wisconsin, Milwaukee, published something different about his local population of yellowthroats: Females seemed to be targeting the size of males’ black masks to determine whether they were worth a fling. That didn’t make sense, because the black masks are generated from melanin, which has no connection to health. “I was taken aback,” says Dunn.