@jayjds2 I'm not sure if you've discovered an answer to your question in the months that have passed since you first posed it, but I asked my friend who has a PhD in ornithology yesterday, and - while he could not offer a concrete explanation - he assumed it was related either to molting, or the sequence of males' plumage development. Unfortunately, I do not know the age of this particular individual, which would have been an important piece of information that could have either supported or negated his speculation. In any case, he was reasonably certain that it wasn't anything aberrant, e.g a strange color morph.
