The American Goldfinch is an abundant and widely distributed species that regularly visits backyard birdfeeders. The type of habitat preferred by goldfinches for finding their favorite foods and preferred nesting sites can be described as weedy fields, orchards, and suburban yards.
Goldfinches forage for food during the daytime, usually in the company of other species. During winter months these roaming flocks can include large numbers of individuals, and in some cases include other species like chickadees and sparrows. Flocks seem to move in rolling, “leap-frog” manner that is beautiful to watch as they traverse open fields. If it seems like you have American Goldfinches at your feeders for much of the day, it is likely they are not the same birds all day, but individuals from a number of foraging flocks for which your feeder is a daily stop. Wintering goldfinches roam over large distances in search of food. Birds living in the north of their range migrate south. Mid-range and southern ones are year-long residents.
Goldfinches are both sexually and seasonally dimorphic. Males molt from muted olive green colors to their bright yellow breeding plumage in the spring. Females maintain their softer hues throughout the year. One of the early signs that spring is approaching is to see the beginning of the transformation of male Goldfinches.
The American Goldfinch is one of the latest breeders, beginning the nesting season in late June or early July. Because the species feeds almost exclusively on seeds, waiting until this time assures plenty of recently ripened seeds with which to feed their young. Because of this timing, goldfinches produce only one brood per season.
Reference: Middleton, Alex L. 1993. American Goldfinch (Carduelis tristis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology.