My chicks are barely 5 weeks old and for the last two weeks one of my Wyandottes has had all her little tail pin-feathers plucked out. We isolated her, cleaned her up, put on Blue Kote and let her heal for a few days. When we tried to reintegrate her, they started pecking her again. We isolated her about three times before we realized that our Mystery Breed roo (we are 99% positive he's a "he") was the instigator. So we isolated him and everyone was peaceful for this last week. Today my son found our little tail-less Wyandotte being chased around and pecked by a few of the Buff Orpingtons. Her tail bloody and featherless (all over again... poor girl was almost healed). She is isolated again. We're just not sure what is going on. All 23 chicks are fed a chick ration at 23% protein. They get treats every morning (hulled millet, raisins, sunflower seeds, cheese). They are in a 10'x9' coop with roosts, water, and feeders available around the clock. The brooder lamp provides them with heat at night (while our nights are still dropping in the 40's). They are let out to free range for about an hour a day so we can keep an eye on them. Why are they pecking? What can we do to make them stop? At 3.9 sq.ft. per bird, they "shouldn't" be overcrowded... especially being they are only 5 weeks old. Any advice would be helpful. We are calling around to see if anyone wants a few chicks as we are willing to give up some if it means they are happier altogether. In the mean time, I'm hoping the geniuses at Backyard Chickens can offer some insight. Thank you!