I had this exact problem not too long ago. I had 5 original girls and then I tried adding 11 new ones (they were about 5 months old). I tried all of the suggestions: sectioning off the coop so they could see not touch, free ranging together, putting them together for the first time at night, places to hide in the run, two feeders/two waterers...I wish I could tell you the magic trick but for me nothing really worked. The younger ones were so terrified all of the time they would just run if they saw the older girls or if they couldn't run they would squish themselves against a wall and bury their heads. They wouldn't eat much, even roosting at night was a hassle. It was awful. I ended up having to just take the three meanest girls and put them in a small coop of their own. It's been 3 months and STILL the young girls go quickly the other way if they see the oldies coming. I don't know if I did something wrong because I see that people integrate all the time. Just wasn't happening here. I wish you much luck cause I know it's not fun watching that happen.
I'm of the opinion that if there's not actual blood being drawn you shouldn't intervene. Chickens are, from our point of view, brutal. A little violence seems to be necessary to them getting it all worked out. I would be willing to bet that if you let them tough it out for a few days (being ready to step in if you should see serious feather-picking or any evidence of blood drawn) they'll learn to get along with each other and it'll be smooth sailing from then on out. If you're worried about them eating and drinking enough, arrange for multiple feed and water receptacles so the big ones can't guard the resources.
I agree, I always let them tough it out, usually in 2-3 days they have established a new pecking order and all is well in paradise again. Quote: