Seasonal Variation in Circulating Carotenoid Pigments in the House Finch

gested (for a detailed discussion of effects of dietary carotenoids on display, see Hill 1992, 1994, Hudon 1994).The latter explanation seems less plausible, but feeding experiments are needed for a definitive test.The second implication of this study is that, especially for species with red plumage, one can test whether a color display is carotenoid-based by examining plasma during molt.Species with plumage coloration that is carotenoid-based should have orange to red plasma.Species with plumage displays derived from melanins or other blochtomes or from feather structures (and lacking carotenoid-based bill or leg color) should have pale yellow plasma.Of course, the best way to determine the basis for color display in a species is to conduct a careful biochemical analysis, but for field biologists examination of blood plasma can provide a quick and useful assay.