As fledglings undergo their fall molt (the Prebasic I molt), their appearance changes from obvious-youngster to apparent-adult. In the middle of that transition, they look a little… wild. It’s a strange and fleeting look, here-today-and-gone-in-two-weeks. We’ve caught enough molting fledglings that I’ve been able to put together a series of photos showing the transition.
Fledgling juncos start out a streaky light brown, with dark bills and yellow gapes.
As they get older, the yellow gape shrinks.