Snow or bare ground, at this time of year I look and listen for two birds visiting from the north, here for the winter. They are both ground feeders, often arriving in cheerful, twittering groups. The American tree sparrow prefers scrubby, brushy spots and is given to melodic twitters in even the worst possible winter weather. And the snow buntings! A flock seen low, over open ground, seems to ride on gusts of wind like so many light-colored leaves, snow infused, rising up a few feet, only to swirl over one another, like the air that carries them.