Specialist Elbru, I ALWAYS appreciate your well-researched posts!!!
I suspected something like this, and had looked over a number of documents from the cornell ornithology lab but somehow didn't find this answer.... Apteria!
When Griffin first came to me I suspected he had been a feather plucker in his previous home(s). He looks in full feather, but does overpreen, especially his wing feathers on the right side- that "anting" behavior where he stuffs small toys and bits of wood or cardboard in the feathers. The vet said he looked great considering his previous diet and containment in a tiny cage.
Because of his prior experiences he was not interested in being touched at all by humans and would lash out at any approaching hand. He had bitten everyone at his foster home who had tried. I made sure to observe his body language closely and allow HIM to choose whether or not he wanted to be touched at all by me... Over the last few months we have built a good trusting relationship and he now solicits and enjoys head scratches.
Once I was able to handle him I found those two strips of "bald" skin on either side of his neck and was a bit worried. Plucking is such a ubiquitous topic on bird message boards, and although I never see primary feathers on the bottom of his cage I do find apx 3 powder down feathers a day. ( the foster folks told me this was normal and when he came to them it was a LOT more. As I said I googled all over the place and did look at a lot of documents from the cornell ornithology lab that pointed toward my hypothesis of those "strips" being naturally feather-free but never found those two images you posted.
I know that showering can help with itchy skin and overpreening, but Griff is terrified of the spray bottle ( apparently it had been used as a punishment in at least two of his previous homes), and although he talks up a storm if I turn on the shower, he leans REALLY far away for the water stream ( pretty clear body language) and. I don't want to force him and make it a more unpleasant experience. We are working on it, and WILL get there ( as we did with handling and stepping up) but it is a slooooow process.
He is going through a molt right now and has molted out most of his head and neck feathers, and is starting to get new primaries on his left wing. The first one worried me a bit as he can be kind of "violent" with his anting behavior and seemed to bruise the shaft, but the feather seems fine now that the blood has receded. Two more new blood feathers on that side now, but so far none on the right ( which doesn't seem in line with what I read on Dr. Ron Hines' site), but he did come to me with his wings pretty badly butchered from a former caretaker's DIY home trim and I had to take him to the vet to have that sorted out back in January. So I just have been keeping an eye on it( lifting the wings every day and taking a peek, no petting or anything).
I didn't mean for this to be such an extended post, but was SO excited to finally have a word for those featherless strips on his neck ( not visible unless I move the feathers to the side with my fingers) - Apteria!!
Thanks again Specialist Elbru!