Below some photos of last week, illustrating how to age some birdspecies
Swainson's Thrush, hatching year; apart from this SWTH showing juvnile greater coverts another additional feature is the buffy tipped feathers under the 3 alula feathers, as shown above. Some HY Swainson's Thrushes show these buffy tips, but certainly not all of them. So it cannot be used as a single ageing feature alone.
House Wren, hatching year; not the most obvious moult limit in the greater coverts but as you can see above the three outer greater coverts are retained.
Marsh Wren, hatching year; as with the House Wren this Marsh Wren has got 3 retained outer greater coverts.
Rose-breasted Grosbeak, hatching year male; note the moult limit between greater and primary coverts.
Blackpoll Warbler, after hatching-year male; note the lack of a moult limit in the alula feathers with this individual.
Magnolia Warbler, after hatching-year male; all feathers look uniform, without any contrast (no moult limit in A1/A2)
Scarlet Tanager, hatching year male; this bird already started to get black feathers on its back and head, quite early for a hatching year!