Hi Georgia, Nancy, great info about blue birds.
I saw this on the web
Bluebird FAQ and it suggests that if there is food and shelter the bluebirds will overwinter in the northern areas. I am so inspired now to get some boxes and mealworm for next season. I just love the birds, we have lots that come around and we love to feed them, many woodpeckers, cardinals, blue jays, etc. Haven't seen any bluebirds here, but we have lots of hawks, so maybe with some boxes...