I have 20 chickens (Americana) and 10 Guinea fowl. I have raised them as a group since they were day old. All the birds free range during the day. They have a large barn area to roost in so they are not cramped. All was well until a couple of days ago. My rooster started attacking a guinea hen. He would have killed it had I not heard the ruckus and intervened. The rooster behaviour is continuing as he attacked another guinea today. This evening I put the rooster in separate quarters and I am trying to nurse the guineas back. Any ideas as to why the rooster would become so aggressive?