There is a great deal of literature regarding how to seperate "first-year"
(birds prior to their second or definitive prebasic molt) from older birds,
although the criteria are mainly for use with birds in the hand. This is
summarized in the Birds of North America species account for this
species. However, to the best of my recollection (I don't have the
literature or BNA account here, although I wrote the plumage section for
this account) first-year goldfinches do not replace their primaries,
secondaries or rectrices, i.e. they retain their juvenal flight feathers.
During the second or definitive prebasic molt, older goldfinches replace
their flight feathers with new flight feathers that are blacker than are
juvenal flight feathers. Thus, through binoculars, you should be able to
distinguish at least some first-year goldfinches from older ones in this
way.


Chris Thompson
Research Scientist, WA. Dept. Fish and Wildlife