Bullying Chicken

[Klzeer]

I have 4 chickens of different breeds. They are 7 months old and I have just noticed that one of the birds, a Plymouth Rock, is bullying at least one of the birds quite badly. The Easter Egger has bald, sore looking patches around her tail feathers and I've seen the Plymouth Rock quite aggressively pecking at her. I have just separated the bully from the others, but I don't know how to solve this problem. Suggestions welcome...

 

[ChickenCanoe]

How big is their space (sq. ft. of coop and run inside dimensions).

What is their feed protein % and what other feedstuffs?