Nobody has been hurt, but oddly enough my Polish girls are most dominant over the orpingtons & brahma. Our 11 week old ladies & 8 week olds do share the same coop. There is a definite pecking order with 3 polish hens at the top (huh?), but they all free range our oversized backyard almost all day. My 3 week old girls are kept where the older ladies can see them, but not touch. I know they'll get chased & scared by their big sissies so I want to wait until they have some decent size on them before letting them mingle. My Ameraucana & ee are in this youngest group. If there are too many problems in the coop, i can put a wirecloth wall right through the middle as each end of the coop has its owm 100 sq foot run. Bullying was a main concern in the design process. I hope it doesn't come down to that!