I just saw this on an ABA blog post (here) where a junco had a slight difference in the wing bars on its right and left sides (there's video of the bird if you want to see). I guess it could just be a few feather tips missing?
I had never heard of that before, and wondered if others have heard of or observed asymmetrical markings.
I had never heard of that before, and wondered if others have heard of or observed asymmetrical markings.