The snowbirds are back. They've been drifting into Missouri over the past month as a series of Arctic fronts drove them from their Canadian homeland. More properly called dark-eyed juncos, these small, hardy birds will sustain themselves on seeds that they find in open fields, among streamside thickets or beneath our backyard shrubs. Free to move on to southern climes, they are content to winter in the cold, gray Midwest and, come April, will escape the balmy air to return to the cool Northwoods.