While this species does accept cowbird eggs, its biology still provides a double dose of protection that helps it cope with nest parasitism!

The American Goldfinch has a very late nesting season. One suspected reason for this involves one of its primary food sources, thistle seeds, which do not mature until July and August. This is later in the season than most female cowbirds lay eggs, so few goldfinch nests are parasitized.

Because goldfinches feed their young a regurgitated paste of seeds, rather than the insects that most young birds including cowbirds require, young cowbirds in goldfinch nests suffer a protein deficiency and seldom if ever survive.