Most of the eastern bluebirds that spend summers here, head south of New England for the winter, some as far south as Cuba. Handfuls of bluebirds stay through winter along the coast and around Great Bay in southeastern New Hampshire, where the climate is more moderate, although only slightly so. Their winter diet favors fruits of sumac, bay, cedar, juniper--any shrub that bears fruit. The pickings are slim this deep into winter.
So, it is always a treat to see the brilliant blue of bluebirds in late winter. These must be the hardy ones, able to survive the wind and cold. The Cornell Lab of Ornithology says that wintering bluebirds will roost together in a cavity. They reported one case where 14 bluebirds roosted together with their bills all pointed toward the center, like a football huddle.
Huddling against the wind seems to be the best way to survive the cold winds of winter. My friend Laurie Hill sent the following photo of bluebirds huddling outside her window in Newfields, in the next town over from ours.