The goldfinch is a common visitor to bird feeders through out the United States. They are strictly seed eaters rarely consuming insects. At feeders they prefer thistle and nyjer seed. The breeding season for goldfinch comes later then many other birds, usually June or July. This is an advantage because this is typically around the time when plants like thistle are in bloom. The thistle seed provides food for the chicks and adults while the stringy substance that is attached to the seeds is often used in nest construction.
The goldfinch is the only finch that molts its feathers more then once a year. Molting is the process by which birds replace their feathers. Feathers are not living tissue, they are sort of like our hair, if they break they can not be healed. To make sure that their feathers stay in tip top shape birds molt once or twice a year. Birds that molt twice a year usually do so because they have more colorful plumage for the breeding season. In the species that molt twice both male and female will molt however it is usually much more obvious in the male. The bottom photo was taken in March when goldfinch are just beginning to molt into their summer breeding plumage. The top photo was taken at the height of the breeding season when the males are almost a neon yellow color.