Hawk skin sends UV signal.

The patch of skin above a hawk's beak just looks orange-yellow to us, but to another hawk, it may broadcast ultraviolet (UV) sex appeal.

For the first time, researchers have shown that this bit of skin, called a cere, strongly reflects light in the UV range. The UV reflection isn't as bright as the orangey light coming from the patch, but it's distinct, report Francois Mougeot and Beatriz Arroyo of the Center for Ecology and Hydrology in Banchory, Scotland.

Many researchers have focused on orangey carotenoid pigments in both the plumage and the fleshy decorations of birds as possible signals of mate quality and sexiness. But studies have also shown that some of these features, such as grouse combs, flash UV.

Mougeot and Arroyo tested cere reflectance in wild male Montagu's harriers in France. The ceres do reflect UV,, especially in males from pairs that start nests early in the season, the researchers report in an upcoming Biology Letters. Other researchers have linked early nesting to greater breeding success. Thus, suggest the researchers, a bright UV cere may signal a prime male harrier. Mougeot and Arroyo haven't tested harriers for UV vision, although many bird species can see light in that range.--S. M.