Odd Juvenile White-crowned sparrow

At least I assume this is an aberrational White-crowned. I've never seen one with this white patch at the base of the neck. Anyone have any ideas?

Taken through a window in very low light, at ISO1600, so pretty grainy.

That's a new look for me and we have a lot of juvie white-crowns here in the winter.

I have never seen this, but I assume they do transition like this at some point.

neat, Jim, looks like a partially leucistic bird, lacking pigment in some of the nape. I've seen this in juncos and robins (although it always expresses itself differently in terms of where the white is). in some cases it's genetic, in others it represents some sort of stress when the bird was growing the feathers--in this case I'd guess genetic. definitely not part of a normal plumage or molt transition.

I agree with Brian as regards the likelihood that this is local leukisic mutation in an LBJ. There is no evidence that stress, per se, can cause failure of melanin deposition in feather epithelium, although mild to severe keratin dysgenesis caused by stress can result in barb, barbule, and even rachis malformation of feathers growing during the stress episode. At least two viruses (psittacine polyomavirus and avian circovirus) that can infect the feather follicle epithelium can cause not only keratin dysgenesis but also local failure of melanin deposition; before the viruses were identified and their pathogenic effects determined, such lesions were sometimes ascribed to the effects of stress.
Dave Graham, East River, SD. ( Wldf disease researcher, pathologist, and diagnostician, Retired)