Today my dog chased and killed two of my 8 week old chickens. He has never chased any of my adult chickens. Do you think it was that they were not full sized and more vulnerable? Do you think it is instinct to chase the younger birds because he knows the adut birds willl peck him? I am hoping this does not worsen. my adults free range.The eight week olds are in a pen that had an opening so they got out and the chase ensued. Any advice other than the obvious? Thanks...