[carsmarco252]

I have three chickens and introduced a cockerel (by mistake). The chicken were dominant but about a week ago the cockerel took the lead. Two days ago i noticed my best layer and friendliest bird had all her feathers plucked out her head and was bleeding. I thought i would just monitor it. Unfortunately every time i have been back to the run since the chicken has more and more feather loss, and now has a very deep wound down to her skull. Does this sound like the work of the cockerel? The other chickens don't seem to be bullied at all and they don't seem aggressive so im assuming it must be the cock bird. The hen is also now very scared of him and flaps onto my shoulder to escape him. I bought chickens for the eggs and have become rather attached to them, last thing i want is a nasty cockerel picking on them and injuring them

[Chookiechook]

It proabably started as a over vigerous hanging on from the cockerel and now there is an injury the other hens have probably started having a feed too

Really when there is an injury you need to separate the bird, spray with purple spray and let it have a bit of time to heal before leaving the bird with the others

If you do that now hopefully she will be ok   I assume the skull isnt showing 

[CluckyChicken]

our cockrel stands on the girls sometimes randomly,  and I think it is a dominance thing?  maybe one she has been separated and re-introduced things will be better

[orchardlady]

Cockerels often favour certain girls and will 'bonk' them stupid. As suggested this was probably a bit of inexperienced over enthusiastic holding on as he 'performed'. You mention that you bought hens for the eggs and the introduction of the cockerel was an accident. You could humanely dispatch him or re home him..not such an easy thing to do..however once he is out of the picture you may find that one of your girls becomes very dominant. Going back to your injured bird. If you can separate her from the rest but keep her in view that would certainly give her wound some time to heal.
Frankly if it were me with this problem I would get rid of the cockerel.