I think they just like to remind each other who's boss. I've got 6 hens in one run that were raised from chicks together. They are over a year old now (gotta be..), been laying for a long time. A couple of the bigger hens occasionally pick on the smaller ones. Different breeds too. No blood or flying feathers. More like a "I'm eating here back off!" or a "I'm walking here get out of my way!".
But at night they are all friends and roost together.
But at night they are all friends and roost together.