There are 7 pullets. 3 are 38 weeks (BO, RIR, and the chicken in question; a single comb light brown leghorn - Misty). 4 are 23 weeks (BO, Australorp, SLW, and BR). They live in a 6x8 coop on a single roost. There is a 12 x 16 completely enclosed run and a larger fenced in area so they are not cramped. They eat layer pellets and crumble with a few handfuls of corn per week and the occasional bowl of yogurt and a cabbage. We live in NC and it's been unusually cold the past 2-3 weeks. It was 18 this AM. The coop is insulated, well ventilated and not heated. Misty has always been very animated and in charge. She also picked on the younger chickens quite a lot when they were younger. They are completely integrated at this point and everyone seems to get along well. Her status has definitely been lowered and she doesn't seem to pick on anyone anymore. I also have not seen anyone picking on her. The feathers started disappearing about 1 week ago. It continues to get worse. They are in places that she couldn't get to (back of her neck and the base of her comb) so in my mind it's either someone picking on her or it's a parasite of some kind. We have dusted her with Sevin a couple of days ago. She also had some damage to her comb a couple of weeks ago, got pale in the middle and had what looked like scabs on it. It has gotten better. The missing feathers are in fact missing, they are not on the ground anywhere. We have had no health problems with any of the chickens. They have not been exposed to any other chickens (ever) or other people who have chickens (2-3 months). So, my questions are: 1) Is this damage from another chicken or some kind of disease. 2) It it is a disease, how do I treat it? 3) If it is damage from another chicken what should I do (if anything)?