CONICET | Buscador de Institutos y Recursos Humanos

Achromatic plumage (white, grey or black) is a good candidate signal for visual communication, yet it is relatively less studied than melanin and carotenoid based, or structural plumage. Here, we sought to determine whether the white plumage of the White-rumped Swallow, Tachycineta leucorrhoa, exhibits variation within and between sexes. Previous recent research in the congeneric Tree Swallows, found that white plumage brightness is related to the bactericidal capacity of individuals´ plasma thus revealing its potential as a signal of individual quality. We removed five to seven feathers from the breast, belly and rump of eight males and 15 females breeding inChascomús, Argentina (35°34?S, 58°01?W), measured their reflectance in the lab using an Ocean Optics USB2000 spectrophotometer, and applied an avian visual model to estimate chromatic and achromatic contrasts among body regions. We compared colorimetric variables (hue, UV-chroma and brightness) with t-tests and calculated units of ?Just Noticeable Differences? for each body region, sex and between sexes. In addition, we performed a multi-response permutation procedure to generate a ?null? distribution of expected values against which we compared the observed values. We found evidence of significant sexual dichromatism in the belly, breast and rump of breeding White-rumped Swallows. Females showed more brightness in belly, whereas males showed more brightness and greater reflectance in the 300-400 nm interval in the breast; sexes were also different in the rump.These variable traits could, therefore, be subjected to sexual selection in this socially monogamous yet sexually promiscuous species with high rates of extra-pair paternity.