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.
They molt their body feathers first, acquiring reddish backs and dark wings, but retaining the streaky head instead of an adult’s dark hood.
When the molt starts on the hood, it generally begins near the bill.
Sometimes we catch fledglings repeatedly and we can see how their molt has progressed over time.
I love the strangeness of the mottled-hood look. The patchy randomness is something you hardly ever see on birds, which generally have crisp patterns or at least systematic spots or streaking, with variation rare. Each of these molting juncos looks a little different from the others. And these birds will only have heads covered in dark and light spots for a short while, just once in their lives.
The last light feathers to remain are usually somewhere near the ears.
Once those feathers are replaced with dark ones, it’s just about impossible to distinguish the fledglings—the juveniles—from adults. One clue is that the juveniles tend to have more brown in the dark of their hoods.
Of course, some adults can have very brown hoods too. That’s one reason it’s important to band the juncos: so that when we see a dark-headed bird, we know how old it is. I recently resighted IRKA in my binoculars and he looked completely adult, but I’d seen him with his mottled head earlier, so I knew better.