I was lucky enough to be around when two ASY female Chestnut-sided Warblers were banded recently. I named them Bird 1 and Bird 2. Though there were a few differences, the birds turned out to be the same sex and age. The bander used cues such as the greenish-yellow crown, dull black facial
markings, and the chestnut that doesn't go beyond the base of the
legs. Not often you get the chance to see that many in hand!