The important thing is to not stress out about it, if you show any kind of reaction or be displeased about it, watching him do it and trying to get him to stop may only make it worse, they pick up on so much that we do not realize so its best to not give it any attention and just act as you usually do, I know it hurts you to see him pull or bite off those feathers but he is still the Issac you know and love even if he is more ragged looking.