In species (e.g., American Goldfinch, Indigo Bunting, Rose-breasted Grosbeak, Purple Finch) in which adults are still molting at this time of year, we look at the appearance of the as yet unmolted feathers and try to determine the feather generation of particular feathers that we know would be retained juvenal feathers (or distinctive-appearing first basic, or first winter plumage) in the case of SY birds.   Sometimes these differences are quite subtle, but in the case of male Purple Finches, the differences are fairly obvious.

PUFI males have what is called delayed plumage maturation, which means that they do not acquire male plumage traits until they are more than one year old (i.e., at the time of their definitive prebasic molt, which is their first complete post-breeding molt)--until this time they resemble the brown-streaked females.  Thus, a male PUFI that is replacing brown juvenal and first basic feathers with new raspberry-colored feathers is an SY, while one replacing old purplish feathers with new ones is an ASY.

Now you know the age of the PUFI (banded today) whose wing is shown below.

Having already completed its prebasic molt, which ordinarily replaces the scarlet body feathering of its spring plumage with olive feathers above and yellow below, this bird (photo below) showed several patches of bright yellow-orange on its head, throat, back, and breast.  This plumage variation probably results when tanagers feed heavily on Tartarian Honeysuckle fruits while they are molting.  A red pigment (rhodoxanthin) in the fruits is very similar to normal yellow carotenoid pigments and becomes incorporated with them in the growing yellow feathers, effectively dyeing them orange.  Although much less common in tanagers, it is the same diet-related phenomenon responsible for the orange tail band variation in Cedar Waxwings and for orange-breasted Yellow-breasted Chats.

In the series of pictures below, 1) an HY SWTH with juvenal coverts lacking any "teardrops" is on top (note, however, that covert second from the right has been molted, i.e., is nonjuvenal); 2) an HY with the classic "teardrop" juvenal coverts is in the middle photo (but note that on the outer coverts the buffy spot is less centered on the rachis); and 3) a very unusual AHY (confirmed by its complete skull pneumatization) showing numerous buffy spots, most of them small and off-centered, but including some large, centered, teardrop-shaped ones on its median and lesser coverts.  This shows why it is important when ageing birds by plumage (i.e., molt limits) that the patterns often associated with juvenal feathers are not too literally interpreted.