We have 3 hens about 20 weeks old that grew up together from chicks. Suddenly one just started abusing another one pretty bad. It stalks it, pecking it, ripping out feathers, and sometimes pins it down in a corner and literally stands on top of it pecking away at it's head. Is this normal behavior to establish dominance? Would I know it's a rooster at this age? I've been reading about how to tell it's a rooster but don't see any signs yet? Should I split them up or something? Thanks.