Igl, Lawrence D., Douglas H. Johnson, and Harold A. Kantrud. 2006. “A Historical Perspective: Changes in Grassland Breeding Bird Densities Within Major Habitats in North Dakota Between 1967 and 1992–1993.” In Prairie Invaders: Proceeding of the 20th North American Prairie Conference, University of Nebraska at Kearney, July 23–26, 2006, edited by Joseph T. Springer and Elaine C. Springer, 275–295. Kearney: University of Nebraska at Kearney.