In its dulled down winter plumage the American goldfinch surprises bird watchers at feeders and in the field this time of year. Rolling across New England in nomadic flocks the American goldfinch turns from eye-popping, sunshine yellow in the summer to a drab, off green in the winter. Known as “bimorphism” it is the most extreme plumage transformation of any New England finch. But look close at the tight formed body, less puffy than a sparrow, with its thick, seed-cracking bill, and striking white and black wings. Male goldfinches retain a sunset of yellow below their bill and behind their eye even in winter. Surviving on an almost exclusively seed diet goldfinches love thistle feeders or a thistle seed “sock” and when scared off the feeder fly away in a characteristic, bounding flight calling softly, "chewwwwy?"