The evolution of colorful plumage in the house finch.

I studied female mate preference in relation to male plumage coloration in the House Finch (Carpodacus mexicanus). Males from an introduced eastern U.S. population averaged significantly brighter in plumage coloration, and males from an introduced Hawaiian population significantly drabber, than males from the parent population in California. Males from Guerrero, Mexico displayed a mean coloration similar to that of males from the eastern U.S., but with a much reduced color-patch size. In controlled feeding experiments, I found that male house finches from all populations possess the same potential to display bright or drab plumage and that variation in plumage coloration (but not patch size) reflects the type and quantity of carotenoid pigments ingested by individuals during molt. In the wild, male plumage coloration was correlated with parental investment and viability. In laboratory and field experiments, females from all populations chose the most brightly colored, largest patched males available, regardless of the appearance of males in their population. A phylogenetic analysis indicated that the small patch size displayed by Mexican House Finches is derived from a larger patch size, and indirect evidence suggests that small-patched males may have access to smaller quantities of carotenoids than large-patched males. These results support the hypothesis that plumage coloration evolved via intersexual selection as an indicator of male quality. In addition, the lack of conformity between male appearance and female preference among populations provides evidence against species isolation models and runaway sexual selection models for the evolution of male display traits.