I have 26 12-13 week old EEs. They are pecking each others' tail feathers out, and one bird in particular is now bleeding on it's bum. They are free fed grower crumbles and given a handful of scratch every afternoon for a treat. They live in a 10 x 6' dog pen attached to a circular run 30' in diameter. I feel they have plenty of space for now, though we're working on an much larger pen for them. Why are they doing this and how can I stop it?