Geographic variation in the carotenoid plumage pigmentation of male house finches (Carpodacus mexicanus)

Geographic variation in both the colour and pattern of carotenoid plumage pigmentation displayed by males in two subspecies of house finches ( Carpodacus mexicanus frontalis and C. m. griscom ) was quantified. The extent of ventral carotenoid pigmentation (patch size) differed markedly between these two subspecies; frontalis males from the U.S. (New York, Michigan, California and Hawaii) displayed a medium patch extending from their throats to their lower bellies, while griscomi males sampled in Guerrero, Mexico displayed small patches restricted to their throats. Frontalis males sampled in Michigan and New York and griscomi males were relatively bright in colouration, while frontalis males sampled in Hawaii were relatively drab. Populations of frontalis in California showed substantial local variation in average male colouration: in two areas only 12 km apart males were as colourful and as drab as any population sampled. In aviary experiments in which they were fed either a plain seed diet or a diet supplemented with red carotenoid pigments during moult, males from all populations converged on a similar appearance, except that griscomi males attained a brighter plumage than frontalis males when their diet was supplemented with red pigments. Regardless of diet, the difference in patch size between frontalis and griscomi males persisted after moult in captivity. The author concludes that the difference in patch size between frontalis and griscomi males reflects genetic differences between these populations, but that the differences in the mean plumage colouration of males among populations reflect differences in the access that males have to carotenoid pigments during moult.