Part 4

_Eastern species._--Only _Sylvilagus floridanus_ and _Peromyscus leucopus_ can be identified as species primarily associated with the eastern deciduous forest. The former is limited in northwestern South Dakota to brushy habitats in riparian communities, whereas _P. leucopus_ is restricted to relatively good stands of deciduous timber and presently is known to occur only in Deer Draw of the Slim Buttes.

Throughout its known range in the western part of the Northern Great Plains, _P. leucopus_ is represented by small and disjunct populations associated with riparian deciduous timber. The known population nearest to Harding County is on the Black Hills to the south; next nearest are several isolated or semi-isolated populations along the Yellowstone River in eastern Montana. Presumably, this white-footed mouse spread northwestward into the western part of the plains region along river systems, in company with deciduous trees, in some post-glacial period when the climate was warmer and wetter than now. Subsequent drying altered substantially the distribution and perhaps composition of riparian forests, and isolated populations of _P. leucopus_ evidently survived only in restricted areas, such as Deer Draw, many of them probably marginal habitat for the species.

_Unverified species._--If the 10 species listed as of "unverified occurrence," it seems highly likely that as many as eight will be found to occur, or occurred within historic time, in Harding County. Among these eight are one steppe species (_Vulpes velox_), three with boreomontane affinities (_Sorex cinereus_, _Gulo gulo_, and _Lynx canadensis_), two (_Sciurus niger_ and _Urocyon cinereoargenteus_) that are associated with the eastern deciduous forests, and two (_Sorex merriami_ and _Lagurus curtatus_) that are Great Basin elements.

It is noteworthy that the last-mentioned faunal unit is not known to be represented in northwestern South Dakota.

ACKNOWLEDGMENTS

For assistance in the field, we are especially grateful to the students who were enrolled in the Field Course in Vertebrate Zoology at The University of Kansas in the summers of 1961, 1965, and 1970, and to M. A. Levy, R. R. Patterson, and T. H. Swearingen. In 1965 and 1970, the summer field course was supported in part by grants (GE-7739 and GZ-1512, respectively) from the National Science Foundation; Andersen was supported in the field in 1968 by a grant from the Kansas City Council for Higher Education. Personnel of the U.S. Forest Service (Sioux Division, Custer National Forest), particularly District Ranger Timothy S. Burns, were most helpful to us in the field, as were Wardens Wesley Broer and Merritt Paukarbek of the South Dakota Department of Game, Fish and Parks. Robert Kriege, Federal predator control agent stationed in Buffalo, was most generous in sharing with us his knowledge of rodents and carnivores in the area, and many present or former residents, particularly Carl Cornell and Spike Jorgensen, also provided useful information and were helpful in other ways.

Ectoparasites reported here were identified by Cluff E. Hopla (fleas), Richard B. Loomis (chiggers), and Glen M. Kohls (ticks). Other than mammals housed in the Museum of Natural History, we examined only three, two in the U.S. National Museum (USNM) and one in the collection at South Dakota State University, Brookings (SDSU).

LITERATURE CITED

ANONYMOUS

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