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Why are Cardinals so red and Goldfinches so yellow?
When I first hear that diet helped make Cardinals red, I found it hard to believe. So I decided to research the subject. I e-mailed the Cornell Lab of Ornithology public information section as well as googled the question. What I found is that diet does indeed influence the color; not only male Northern Cardinals but also male American Goldfinches. Carotenoid pigments in the diet affect bird color
Researchers have discovered that Cardinals fed a diet with no red pigments resulted in their color becoming a much paler red. When Goldfinches were fed a diet with more red pigments they became a more orange color. To read about the research go to: The Influence of Carotenoid Acquisition and Utilization on the Maintenance of Species‐Typical Plumage Pigmentation in Male American Goldfinches (Carduelis tristis) and Northern Cardinals (Cardinalis cardinalis)
Natural History Wanderings 
Makes sense. My aunt used to breed red-factor canaries and when they molted she would change their diet so their new feathers would come in more reddish-orange.
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By: entire leaves on April 11, 2011
at 9:36 AM