I had to rehome some beautiful silver and gold laced wyandottes because they were a bit mean to my other more meek chickens. My barred rocks were a little pushy as well. My Marans were top of the pecking order. Of course, that was probably just my chickens since we had faverolles, bantams, and...
I agree that it may be feather picking. Some possible reasons for this are overcrowding, too much light inside the nesting areas, feeding less than 16-20% protein in a balanced feed or too many treats, not getting outside to roam, and yes, bullies. Some breeds may be more aggressive. Have you...