Proximate Basis of Variation in Carotenoid Pigmentation in Male House Finches

Abstract

In the wild, male House Finches (Carpodacus mexicanus) vary in plumage color from pale yellow to bright red. I investigated the proximate basis of this variation in plumage brightness, as well as the basis for variation in the extent of ventral carotenoid pigmentation. Regardless of their age or coloration in the wild, captive males converged on a similar appearance after completing prebasic molt on a standardized diet, with significantly less variance in coloration than is found among wild males. Captive males that were fed a diet deficient in carotenoid pigments grew pale yellow feathers; males fed a diet supplemented with β-carotene grew pale orange feathers; and males fed a diet supplemented with canthaxanthin grew bright red feathers. Stored carotenoids did not appear to be an important source of feather pigments. Red males captured from the wild just prior to fall molt and fed a carotenoid-deficient diet did not grow more colorful feathers than males that had been held in captivity on a carotenoid-deficient diet for six to nine months prior to fall molt. In a wild House Finch population in southeastern Michigan, the mean plumage coloration of yearling males was significantly drabber than the mean coloration of older males, although both groups displayed approximately the same range of coloration. Wild males tended to become brighter between their first and second springs, but thereafter, males tended to display a similar plumage coloration between years. The extent of ventral carotenoid pigmentation (color-patch size) also was partly dependent on carotenoid intake. Captive males whose diet was supplemented with canthaxanthin produced significantly larger patches after captive molt than before captive molt, and canthaxanthin-supplemented males also expressed significantly larger patches than males in the carotenoid-deficient or β-carotene-supplemented groups. Among wild males, there was a significant positive correlation between patch size and plumage brightness.