BLUE TITS ARE ULTRAVIOLET TITS

The blue tit (Parus caeruleus) has been classified as sexually monochr omatic. This classification is based on human colour perception yet, u nlike humans, most birds have four spectrally distinct classes of cone and are visually sensitive to wavelengths in the near-ultraviolet (30 0-400 nm). Reflectance spectrophotometry reveals that blue tit plumage shows considerable reflection of UV light. For example, the blue cres t shows peak reflectance at wavelengths around 352 nm. Furthermore, th e blue tit is sexually dichromatic for multiple regions of plumage, in cluding the crest. Choice trials performed in the laboratory indicate that females prefer males with the brightest crests. This study has im plications for both intra-and interspecific studies of sexual selectio n, as well as future classification of dichromatism, which should not ignore the possibility of variation in reflectance in the UV.