Breeding season changes in a bird’s physical appearance can involve more than a set of new feathers. The colors of birds’ feet, legs and bills can also change in different seasons. One transition most people are aware of is the European Starling’s bill which is black in winter and turns yellow as the breeding season approaches. Male and female Evening Grosbeaks also undergo a change in bill color, from bone-colored in the winter, to a greenish hue in the spring. Hormones are largely responsible for these pigmentation changes which often play a role in courtship behavior. Usually change in the color of the bill is most pronounced among birds which retain the same plumage color and pattern throughout the year, such as starlings and Evening Grosbeaks. (Photo-female Evening Grosbeak)
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