I have this one hen who keeps pecking on this one particular chickens neck. I keep noticing it, she started a few days ago and I thought that was strange now she's constantly doing it. She only pecks at this one particular chicken, I brought the pecked chicken in the house and examined her neck(that's where she's been pecking) and don't see any bumps. They are all debeaked. She doesn't really peck at her neck she really grabs the other chickens neck with her beak and holds it for a few seconds by the time I notice she lets go. The chicken that's getting pecked at makes a lot of noise when it happens. They are free-ranged and have about 2 acres to roam so I know it's not space. But I am going to get them fenced in due to a lot of wild animals around us. What should I do, could I maybe put something on her neck to discourage this? Thanks.