I have 4 chickens from original flock (2010). Recently added two more pullets. Its been about 10 weeks since pullets are here, but the old group is still ganging up on the pullets. They are terrorized, afraid to get into coop, trying to sleep outside etc. Recently a broody member of the flock hatched 2 chicks and were killed. I suspect the the killer is one of the original flock. Anything I can do ? I originally built my coop just big enough for them to sleep. They free range during the day. Is small coop creating the problems ?