I have three 10 week old chicks that I am trying to release in the pen with my three 18 week old pullets, when I first let them loose the bigger chickens attacked them so I put them in a cage in the pen so that they can get use to each other, (they have been in there for almost 2 weeks now) I release them for a little bit every day and the big chickens still try to attack them and pluck their feathers out. I don't know what else I should do I don't want them to kill my chicks. Any suggestions would be great.