 It's the time of year when young birds have left the nest, sometimes accompanied by their parents, sometimes not. A time when they're sporting a plumage that they'll wear for only a short time. And because this plumage is often quite different than what they'll be wearing later, it's also a plumage many of us have very limited experience with.
This first set of real, non-downy feathering is called the juvenal plumage. The young bird is a juvenile, but its plumage is juvenal. Nothing delights "birders in the know" quite like correcting novitiates when the two terms are used improperly. Most of the juvenal contour feathers, particularly those on the head and breast, will be replaced some time in autumn during the first basic molt. The flight feathers of the wings and tail will be retained (along with some of the wing coverts, etc.). These retained feather will often look more like "normal" adult feathers than those that will not.
For some species, like the Song Sparrow, the differences between juvenal and basic are slight enough one might not even notice them. The feathers may look a little "fuzzier" and the pattern "not quite right", but otherwise, they look pretty much like Song Sparrows.
Other sparrows may be a bit trickier and require a closer look. It may even be necessary to see if there are any adults near by to provide clues.
Of course, sometimes the juvenile hanging out with adults doesn't quite match up with the adult that appears to be attending it for reasons that have nothing to do with plumage...
Some nestlings don't even wait until they've fully grown into their juvenal plumage before they venture out into the world. These chicks will not only have a different looking plumage, they'll be smaller and shorter beaked. So, along with a plumage that doesn't match the adult, structurally they'll look very much like a different species, too.
And for some species, the addition of a juvenal plumage will make an already complicated identification problem even more problematic. Juvenal stages are often the most poorly illustrated plumages in a field guide, if they're included at all. And a single, out of place juvenile can send one's imagination running off in unproductive directions.
So, this fall, while you're sifting through the migrant passerines, crowds of shorebirds and the common species that we often take for granted, watch out for the youngster.
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