Jealousy?

[Punky84]

Also, check them for mites or lice. That might be grooming.

You can try isolating the one doing the picking for a while. I had a hen picking the feathers off of a rooster's neck one time. They were on a perch during the day and he just let her. I locked him up overnight. I never saw her picking his feathers again. Usually I isolate the aggressor but she was laying eggs and he wasn't so I let her have access to the nests.

Negative on lice, mites

 

[Punky84]

I'd see about adding a bit more clutter, the stuff that is there is fairly small and not actually breaking line of sight from one side to another.

I'd also up the protein to see if that helps.

Since you know the one bird has been having shelling issues, I agree that it'd be a good idea to try giving her a calcium citrate tablet daily for a couple weeks to see if that fixes the shell issue - if it does, then she simply needed more calcium than she was taking in - not sure if you put out oyster shell or crushed eggshell for them, but some birds may need more than the amount provided in layer feed. If calcium supplements don't fix the shell issues, then the problem is internal and adding extra calcium won't help her.

Thank you. I will do all that. They have oyster shell, but don't touch it much. Not sure why. I have tried it in different places in the run. But not really touching it.