Hello experienced chicken-keepers! We noticed the other day that our Australorp hen had a black spot on her comb, surrounded by a slightly paler area. I did some Googling and convinced myself it was a spot from being pecked, but today one whole peak of her comb has turned black and there are a few other black spots too. Is this fowl pox? Could it be frostbite (it's getting under freezing here at night but their coop is well ventilated)? Should I isolate her or take her to the vet?