Cannibalistic chicken?

[planika]

Hello.
We had 6 egglaying hens (now we have 4), around 30 weeks old. No rooster. They are behind a fence through the day and in the evening we let them out in the backyard. We have raised hens like that for over 20 years and never had a problem like that.
A month ago I noticed blood on beaks of two of our hens. Later I found out they can be cannibalistic! Crazy! Well we killed the most agressive one, since we didn't have enough knowledge about it at the time and it seemed the only solution. But it solved nothing. Another hen (her name is Tesaloniki, very sweet hen) continued vent pecking at already injured hen. Then we removed the injured one and noticed that another hen is having injury on her leg. I suspect that the perpetrator found another victim after the first was removed, because the injury looked fresh. The first injured hen was later put down since her vent wound wasn't getting any better. Then we isolated Tesaloniki (She is now in the backyard the whole day and when the others are let out, we close her in her sleeping chamber where it's dark. It's only an hour before she would go in otherwise). After a week of isolation we tried to put her back with others and the first thing she did was pluck feathers off another hen's bottom. She couldn't have been bored since she was out all day... right? And the feed is the same as it has always been. She also has weird feathers on her back that i don't know the cause of. I noticed it abouth a month ago and it hasn't got better or worse since. I have put a picture of her feathers here. Oh and she lays an egg every day. (English is not my first language so some things might sound awkward. Thank you for your patience.)
How can I prevent her from plucking other's feathers? And do you know the cause for her feathers looking like that.

 

[BlindLemonChicken]

Removing the bullied hen will only make things worse because when she returns she will be at the bottom of the pecking order. Better to remove the bully.

Since you are seeing this problem repeatedly I would think it was more an environmental problem than an individual chicken problem. They will peck for lots of reasons—boredom, lack of space, lack of protein are things I can think of off the top of my head.

So it would help to know the dimensions of your coop and run, what you are feeding and what breeds the chickens are. Pictures would also be good. The feathers could look like that from molting or mites. I don’t have experience with mites but I’m sure someone else will chime in if that’s the case.

 

[BlindLemonChicken]

Am I understanding this right or is the bully the one you removed who also has odd looking feathers?

 

[BlindLemonChicken]

If she is laying every day the feathers are probably a mite issue so hopefully someone can help advise on that. I know mites are easier to see at night when the chickens are roosting—if you go out to the coop with a flashlight you should be able to see them moving because they feed at night.