The Sioux, or Dacotahs, of whom the Assiniboins are a branch, pretend that thunder is an enormous bird, and that the muffled sound of the distant thunder is caused by a countless number of young birds ! The great bird, they say, gives the first sound, and the young ones repeat it : this is the cause of the reverberations. The Sioux declare that the young thunderers do all the mischief, like giddy youth, who will not listen to good advice ; but the old thunderer, or big bird, is wise and excellent, he never kills or injures any one !

Western Missions and Missionaries, p. 144