The American Goldfinch changes from winter plumage to breeding plumage by a complete molt of its body feathers. It is the only member of its family to have this second molt in the spring; all the other species have just one molt each year in the fall.
They are one of the latest nesting birds, starting in late June or early July, when most other songbirds are finishing with breeding. Their late timing may be related to the availability of suitable nesting materials and seeds for feeding young.
Brown-headed Cowbirds may lay an egg in a Goldfinch nest, but the hatchling will usually die because the seed-based diet that the parents provide cannot support it.