There is one girl leading the attacks, and a handful of others following the leader, but only one chicken has been the main target.
I got on my favorite backyard chicken forum and spent about half my bedtime reading about how to handle this growing issue. I ended up deciding the solution I was not looking for was culling either the victim or the bully, so I instead went for the isolation method. However, after sequestering the lead bully chicken in a cage within the coop for three days, the nighttime temps dropped into the 20's and it felt cruel to keep her out of the hen house and away from the others' shared warmth, so I let her out............... and she went straight after her victim again.
There are now several girls missing feathers, but the main victim is so intimidated she spends almost all of her day up in the hen house, cowering in corners.
I'm sure- if the weather would allow- I could further isolate the main bully and find some success with her rehab, but it's too cold for me to do that to her without feeling cruel.
Happily there is a fellow chicken keeper nearby who has welcomed the bully into her well-established flock, and tomorrow she will be dethroned and introduced to her new sisters.
I stood out in my coop for an hour and a half this afternoon observing to make sure I grabbed the proper bully (lesson learned- next flock around won't be a bunch of the exact same breed!).
"ChickieB" now waits in the chicken tractor for her relocation, and I'm hoping it won't be a big deal for the mood to change and the bullying to taper off once she's outta here. However, if another girl picks up the torch, I'm going to attempt a sequester in the garage- near Leeloo's space heater for my peace of mind- and see if that'll influence some positive resolution to this drama.
I'm sure my girls will be happy to have a little peace restored to their dailies... and the feathers to their bums! I just hope I've chosen the proper method for solving our problem this time around... learning as you go is hard!