It got really cold here last night (6 degrees) and is supposed to be colder tonight (-7). Of course, their heater went out, too. The birds survived, but I'm worried about frostbite. How can you tell? The are huddled in their roosting area which is small and I'm hoping that between it and the fact I buried the windward side of their coop in snow yesterday that their body heat was enough to keep them warm. But I don't know. What are the early signs and how do you treat it?