This is my first winter with Silkies, and even though we are having a mild winter so far here in Missouri, it has gotten down to 15* here some nights, and my birds are all doing just fine. They are now 6+ months old. I do not use heat or lights with any of my birds, for fear that they will get dependant on it, and if a power outage were to occur, they would be in a world of hurt not being used to the cold. I didn't take these kids out to their own coop until they were 8 weeks old, and that was in the heat of the super hot summer we had! I worry more about the heat than I do the cold. Make sure they are in a draft-free coop, with plenty of deep bedding so they can snuggle in.