How do I stop a pecking order

[oshilo88]

I have some pullets, 12 weeks old. And I noticed that they started pulling off the tail feathers from each others. Today I noticed they pecked it so bad that one of my OE girl was in blood. I washed and disinfected it. She is solated. I included a picture of her. How do I stop that? Why do they do it? Please help.
PS. They're in a big coop, 24 chickens. They have an access to food and water 24/7. Plus I always give them some treats. Vegetables, fruits and half of a pumpkin to peck at

 

[Shadrach]

How big is a big coop. Pictures and measurements would be helpfull.
Do they have a run? Some pictures and dimensions of that as well if you could.

 

[oshilo88]

How big is a big coop. Pictures and measurements would be helpfull.
Do they have a run? Some pictures and dimensions of that as well if you could.

Their coop is 10×10. And yes, they have a run.

 

[janina power]

How is she doing now? I find it interesting you said this is an Olive egger.. Mine have recently started laying eggs and one morning i go and 3 of my olive eggers vent/tail area were pecked to the point of drawing blood. (must have been at least two days)- I made the mistake of not having their nesting boxes in a shady area with walls and curtains.. also some of my roosts in the run, were kind of not too high so if they were ever up on the roost who ever was on the floor would be right at their butt level. I dont know for SURE why or how it all started.. But after seperating all three, I did go back and watch my Roo and the other two hens , and my one Easter egger hen started to try pecking at the other two butts. so i figure shes the one who might have started it all? AGain its all the not knowing that drives me nuts.. I had to seperate her for two days , so far today she is still with the other two.. but my 3 injured are still inside this would be day 4 already.. I do see that they are healing but the tail part has scabs now Im not sure what to do , How is yours doing with the healign process? Im new at this whole chicken thing feelilgn so overwhelmed becuase Ive just never been through this before. Two did happen to lay an egg each so thats a good sign.. the other one hasnt started laying yet though. so just not sure what to do..

 

[FunClucks]

Their coop is 10×10. And yes, they have a run.

Size of run? How much clutter is present? Pics would help us help you.

Even though you meet the recommendations most folks will give on here of 4 sq feet per chicken in the coop, it does vary somewhat depending on your breeds and personalities. Some will need more space. Also, what are you feeding them, feeding routine, and what is the protein level of your feed?