Adding new birds to flock
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The older birds are not going to "know" those youngsters and will look at them as interlopers. I suggest the "look but don't touch" process so they can all get a chance to know each other before you try to mingle them together. This has some information about integrating chickens:
Once you do put them all together, add extra feeders and waterers so the younger ones won't be kept away from eating and drinking. You might also want to put up some sort of escape nooks that the youngsters one can get in but the biggers can't...that way the smaller birds can get away from harassing bigger birds.
Thanks. I am building a bigger coop on one end of my run opposite my current coop. I think I'll put up a temporary divider after moving chicks outside so they can see the others but not touch. Then I'll watch them when we let them free range to see if the little ones are getting bullied.
Sounds like a good plan! The free ranging should help it go easier too since the younger ones will be able to get away from the older ones easier.