My nine-month old pullets have suddenly got black spots on their combs. I'm wondering if anyone knows what these are. Is it frostbite? We live in Michigan and have a 10 x 10 coop and 10x10 covered run for nine chickens. The temperatures have been in the 20s at night lately. Previously we had temperatures around 0° and I didn't notice these black spots at that time. Otherwise they look healthy and are acting normal. They aren't usually aggressive with each other, but since we have been keeping them confined to their coop and run lately after a hawk attack, I have noticed a little bit of scuttling and chest bumping here and there among them. I have not seen any pecking behaviors. We checked their vent area and I could not detect anything that looked like mites or lice.