Plumage brightness in relation to haematozoan infections in the greenfinchCarduelis chloris: Bright males are a good bet

Variation in plumage brightness (yellowness) and prevalence and intensity o f haematozoan infections in greenfinches Carduelis chloris L. were studied in three populations, widely separated in geographic location from Spain to Finland. Sexual dichromatism (SD) in coloration was marked, males being ye llower than females. Although older birds were generally yellower than youn ger birds, the degree of SD in coloration increased with age, perhaps due t o delayed plumage maturation in males. The prevalence of haematozoan infect ions was unrelated to any measure of male plumage coloration, but the inten sity of haematozoan infections was strongly negatively related to male plum age brightness, and this pattern was similar in all three populations. Henc e, male plumage brightness reveals information about the extent to which ma les are parasitized. This result is in accordance with the Hamilton-Zuk hyp othesis, which suggests that bright male plumage has evolved to indicate he ritable resistance to parasites. The fact that lightly-infected males had b righter plumage than noninfected and heavily infected ones may suggest that non-infected males were a mixture of both susceptible and resistant indivi duals, whereas lightly infected individuals might have been effectively imm une to parasites. Our data provide a clear example of the negative associat ion between plumage brightness and blood parasite loads in birds, and sugge st that male plumage yellowness in the greenfinch can function as an indica tor of male quality.