Male eastern bluebirds (Sialia sialis) have two types of ornamental plumage coloration: a brilliant blue-ultraviolet head, back, and wings, and a patch of chestnut breast feathers. The blue-UV coloration is produced from feather microstructure, whereas the chestnut coloration is produced by a...

Carotenoid pigments can directly enhance the immune responses of vertebrates, and they are used by many animals to create ornamental color displays. It has been hypothesized that these two functions of carotenoid pigments are linked: animals must trade off use of carotenoid pigments for immune...