Since it may not be external parasites, overcrowding and feather picking can be the problem. If you're not seeing feathers on the ground, they are eating the feathers. This would suggest a lack of enough protein in their diet. Feeding them gamebird feed will eliminate feather eating and possibly the picking. Coop or pen/run expansion will take care of overcrowding and picking too. Seperating the rooster will help as well, perhaps placing him in a pen/coop next to his hens where he can watch them, eliminating contact. Finally, try using Vick's Vapor Rub IF picking continues after all that I've suggested. Then if the picking still continues, time to cull and stock your freezer.
