American Goldfinch (Carduelis tristis)

Goldfinches are very sociable and often gather in flocks with other birds. Some populations are short-distance migrators and move south in the winter.

During mating season the male goldfinch has a bright yellow body, black wings with white stripes, a black cap on its head, and a white rump.

Females and winter males have duller feathers that are an olive-yellow color. The male's black cap may disappear in the winter or turn a dull black. Females don't have the black cap on their heads.

Small, noisy, seed eating finch
Small cone-shaped, pointed pinkish bill
Black forehead
Eyes yellow
Head, back, breast and belly bright yellow
Wings dark with white wingbars.
Tail short and notches
Undertail white

http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/American_Goldfinch_dtl.html