NatJ is right. It's different in every situation and it doesn't stay the same. With my juvenile pullets and hens (5 1/2 months) the pecking order is changing constantly and now a couple of them are getting brave enough to challenge the old ladies. It is important to have hiding places and escapes. Sometimes you have to isolate the one(s) being bullied, although I found it more effective to isolate the biggest bully. Most of the time it settles down to only an occasional peck to remind them of who's boss, but it pays to be vigilant in case you have to rescue the tormented ones.