Recently something has been attacking my hens and roosters. Whatever it is doesn't kill or eat the chickens, but seems to pull all the feathers off their backs and sometimes some skin along with it. However, some of the damage is so bad that the chickens die soon after the attack. There is blood, but I can't see any scratch marks. The latest attack looked the same on the top, but it was also the same thing on the stomach. A couple of the hens that are fine are missing some feathers and one looks like something tried to bite it at the top of its leg. I don't have any pics. Can anyone give me any ideas as to what might be doing this? Thanks!