OCCASIONAL PAPERS U r of the MUSEUM OF NATURAL HISTORY The University of Kansas Lawrence, Kansas NUMBER 37, PAGES 1-27 JULY 9, 1975 STUDIES OF SMALL MAMMAL POPULATIONS AT THREE SITES ON THE NORTHERN GREAT PLAINS by Jaime E. Pefaur 1 and Robert S. Hoffmann 2 An important North American region, the Great Plains, has been studied by the Grassland Biome of the International Bio-logical Program through a network of study sites ranging from Texas and New Mexico to North Dakota and Montana (French, 1971). The purpose of this study was to compare some of the characteristics of small mammal populations in three generally similar grassland sites in the northern Great Plains. Intrasite and intersite comparisons of grazed versus ungrazed, snap-trapping ver-sus live-trapping, and prebaiting versus nonprebaiting procedures in grid sampling were undertaken. Population density, standing crop biomass, reproduction, and movements were the principal autecological factors analyzed. Acknowledgements The senior author gratefully acknowledges support by NSF Grant No. GA 12415. Philip S. Humphrey made thoughtful com-ments about the manuscript. In the field and laboratory work, we also received help from Alberto Cadena and Peter Lowther. Studies at Cottonwood and Dickinson were supported by a grant to the junior author and J. K. Jones, Jr. from the Grassland Biome section of the International Biological Program, administered through Colo-rado State University (G. M. Van Dyne, Director). 1 Department of Biology, Universidad Nacional de San Augustin, Arequipa, Pern. This paper is based on research accomplished while the senior author was a graduate student at the Museum of Natural History and Department of Systematica and Ecology, The University of Kansas. 2 Curator of Mammals, and Professor of Systematics and Ecology, The University of Kansas, Lawrence, Kansas 66045.