Klicka, John, Spellman, Garth M., Winker, Kevin, Chua, Vivien, and Smith, Brian T., 2011, A Phylogeographic and Population Genetic Analysis of a Widespread, Sedentary North American Bird: the Hairy Woodpecker (Picoides Villosus): The Auk, v. 128, no. 2, p. 346-362.