First post here. I have 2 coops, one short and one tall. The tall one is a couple years older than the short one. The tall coop is on its 2nd set of chickens. Both sets in the tall coop have exhibited the same problem with picking each others feathers out around the base of the tail feathers. All but 1 or two hens will have all the feathers around the tail feather pulled out in every season. In extreme cases, the tail feathers and many up their backs are missing. The first batch of hens had alot of assortment, RI Reds, Domoniques, Barred Rocks and a couple Wyandottes. The Dominique and Rock were very mean. My current assortment is RI Reds, Black Australorps and a Blue laced Wyandotte. All have feathers missing except the Wyandotte. The short coop has never had this problem. The short coop has Buff Rocks, White leghorns, and I think a Columbian. In the past, I tried killing the leader that I saw picking feathers, but then another hen would take her role, and continue with the picking. I have no roosters. I have heard that a rooster will stop a lot of this bad behavior, but I cannot have a rooster due to the noise. Is this behavior due to the hens, due to the assortment, due to the structure differences, or disease in the tall coop? Both coops have roosts, laying boxes, light, food, water, some heat, and are kept clean. Any ideas how to reduce or eliminate this problem would be greatly appreciated.