Papers in the Biological Sciences


Date of this Version



Prairie Naturalist (December 1978) 10(4): 97-112.


Copyright 1978, North Dakota Natural Science Society. Used by permission


It has long been recognized that the Great Plains represent a major transition zone in the distribution patterns of North American birds; field guides traditionally have treated the 100° W.longitude meridian as a convenient dividing line between eastern and western faunas. Furthermore, this line rather neatly bisects the political subdivisions of the Great Plains, namely the "plains states" extending from North Dakota southward through South Dakota, Nebraska, Oklahoma, and Texas. Of these, Texas is the least typical, its climate and fauna is strongly influenced by the Gulf Coast on the east and the Chihuahuan desert on the west. As a result of its size and ecological diversity Texas supports the largest array of breeding bird species of any state in the nation. Thus, in the present analysis it was decided to eliminate from consideration all but the northwestern "panhandle" of Texas, which consists of the grassland-dominated "staked plains." Further, to facilitate the faunistic analysis, limiting lines of latitude and longitude were selected that not only encompassed all five other states mentioned, but also parts of several adjoining ones. After some deliberation, it was decided to define the coverage of the analysis as extending from the U.S.-Canadian border {49° N. latitude) southward to 34° N. latitude in Texas, following this line eastward until it intersects with the Texas-Oklahoma boundary, and continuing eastwardly along the boundary to the eastern limit of Oklahoma. The western limit was defined as the 104° W. longitude meridian, which essentially conforms with the western boundaries of the Dakotas and the Nebraska' 'panhandle", and continues southward through the eastern portion of Colorado and New Mexico. The eastern limit was selected as the 95° W. longitude meridian, which includes the prairie areas of western Minnesota, the western edge of Iowa, and a small part of extreme northwestern Missouri. Where this line intersects with the Missouri River along the Missouri-Kansas border, the coverage was continued eastwardly to include the extreme eastern portions of Kansas and Oklahoma.

The area thus enclosed includes all of five states, parts of six others, and comprises a maximum north-south distance of slightly more than 1,000 mi, as well as a maximum east-west distance of nearly 550 mi. The total surface area includes 502,000 mi2 , or 17 percent of the land area of the 48 contiguous United States. It lies almost entirely within the "grassland climax" as mapped by Clements and Shelford (1939), and perhaps represents about the largest land area south of Canada having a relatively uniform floristic nature that could be established for purposes of analysis. A very similar area was selected for an inventory of the Great Plains plant flora (Barkley 1977).