I have a flock of 15 with 1 roosters. over 50% of my chickens now have bald spots on their lower backs, the size of the bald spots are approx. 4" in diameter, so pretty big. Some of these bald spots are brighter red in areas like it is irritated. Does anyone know what this is from and how to stop it? Lice? Mites? The egg production is still pretty good, getting 8-12 a day but the feather loss seems to be getting worse.