Just about all the birds will put on extra downy feathers under and between their normal plumage to help keep them warm and dry. Back in the fall I go a couple of shots of one of the Langenheim adults and the bird was pretty raggedy looking. Feathers in disarray, kind of raggamuffin looking. Turns out the bird was adding a new layer of feathers in preparation for the coming winter. I've seen it in Northern cardionals too. They look like little red puffballs. Other birds do the same.
