What about your other chickens? If one has them, they all do. To determine if you actually have lice/mites, pick one or two off the roost at night and look under their tail and around the vent with a good flashlight. If there are any, you will see them. As mentioned, Adams products are excellent. I have used Adams Flea and Tick Dip for infestations and it works wonders. The spray is great also. If none of the above applies, it has to be someting else and I would suspect feather picking. Of course, moulting has been mentioned. Moulting can occure at any time of the year, but is most likely in the Fall or early Winter. When I had my flock in south FL, they usually moulted in late summer. Keep looking, you will find the cause.........Pop