UE. Whom ever is the troublemaker stick them in a crate for a minimum of three days while your bird adapts to normal life again.
Yes, the one in the crate is going to get ticked off but that is to be expected.
If after letting it out it immediately goes back to harassing place it right back in the crate.
I have had some birds that took three crate times before either it got the message or another bird came to the aid of the one picking on it to stop it and then that bird realized the gig was up.
There is no such time table when it comes to behavior patterns.
Three days is minimum though imo because most birds who pick on others take at least that long.
You might go four or five days right at first to get the message across.
I have found it on average no matter the days in crate it takes two crate periods.
Thank you for the advice! Here's the deal: We have five hens. The current pecking order, from top to bottom, is: Gertrude (mean mutt), Salma (Welsummer), Maggie (Wyandotte), Effie, and Bonnie (both Leghorns). Effie and Bonnie are younger and were added to the original flock back in June. They are inseparable, of course. Gertrude and Maggie have always been best buds. Salma has always been more of a loaner. What if we isolate Gertrude and Maggie together? That would surely tick Gertrude off less, but would it have the same dampening effect on her aggressiveness? And can we simply lock them in the coop together during the day and only crate them at night? We'd put feed both inside and outside of the coop, obviously.