Looking for a Sunset Bird in Winter

The west was getting out of gold, The breath of air had died of cold, When shoeing home across the white, I thought I saw a bird alight. In summer when I passed the place I had to stop and lift my face; A bird with an angelic gift Was singing in it sweet and swift. No bird was singing in it now. A single leaf was on a bough, And that was all there was to see In going twice around the tree. From my advantage on a hill I judged that such a crystal chill Was only adding frost to snow As gilt to gold that wouldn't show. A brush had left a crooked stroke Of what was either cloud or smoke From north to south across the blue; A piercing little star was through.