1. U.S. Geological Survey, Northern Prairie Wildlife Research Center, Jamestown, North Dakota
2. Department of Zoology, Oklahoma State University, Stillwater, Oklahoma
3. U.S. Geological Survey, Earth Resources Observation and Science Center, Sioux Falls, South Dakota
4. State Key Laboratory of Resources and Environment Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China, and Department of Geography, University of Maryland, College Park, Maryland