I used a wire dog crate to aid in my pullets introduction. They lived in it just outside my girl's run for a week and then I put the whole crate IN the run for a few days and since everyone seemed to be behaving themselves I opened up the door and let them come out when they wanted. They still periodically went into the crate for peace and quiet and my older hens did pick on them a little but nothing too bad. They'd gotten used to them. Slow introductions are always better then baptism by fire.