I have (3) 7 week old barred Plymouth Rocks, (4) 6 week old Buff Orpingtons, (3) 3 week old EE's, and (5) 1 week old Cochin bantams. The 3 week olds are house with the 1 week olds and they get along fine. The first day was a little rough and the "big" babies picked on the little babies but I figured out that they were being possessive over their food and put little cups of food all over their brooder. Once there was food everywhere everyone got along fine. No problems since then. Until now... Although we are still a few weeks away from merging the two different age groups: the 6 & 7 week olds and the 3 & 1 week olds I am starting to think about getting them used to each other. Not the tiny babies but the EE's and the bigger birds. All of my older birds are hens and I see no signs of the EE's being Roo's but that could change of course. My Barred Rocks didn't seem to mind the EE chick I showed them but one of my Buff Orpingtons made this low whistling sound I have never heard from any of my birds before. I am gathering that this sound is a threat because the little EE chick started screaming and got away as fast as possible. She was okay with the bigger birds up until that point. The Buff girl also tried to peck the baby which just furthered my assumption that she was being aggressive towards her. I am new to this and obviously I don't want my birds to be aggressive towards each other as eventually they will all live together in one big coop. Is there a specific meaning to this sound and how can I get the two groups used to one another? Any suggestions? Advice? Please tell me if I am doing anything wrong. I want everyone to eventually live together happily.