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Christian, D.P. 1982. A field survey of Microtus chrotorrhinus in northeastern Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 32 pp.
The rock vole or yellow-nosed vole, Microtus chrotorrhinus, reaches the western-most limit of its geographical range in northeastern Minnesota. The status of this species in Minnesota has been of considerable concern because of the extreme paucity of distributional records and the history of discovery of rock vole populations in the state. The first record of rock voles in Minnesota was of one specimen collected in 1921 in northern St. Louis County. Rock voles were not subsequently reported in Minnesota until the early 1970's, when 26 were captured at a single locality in central Cook County. More recently, the existence of six other rock vole populations in the state (all in Cook County) has been documented.
Despite these recent records, this species' occurrence in the state remains poorly known. There appears to be little doubt that the general distribution of M. chrotorrhinus in Minnesota includes only the northeastern portion of the state; further field work is needed to more specifically document range limits. Perhaps more critical -- and less well understood -- questions concern 1) the abundance or frequency of occurrence of rock voles in this part of Minnesota and 2) the breadth of habitats that they occupy. One reasonable interpretation of available records is that rock voles are extremely uncommon in the region and occur only in small and widely separated populations. However, that conclusion has remained unsatisfactory because of the relative lack of small mammal fieldwork in northeastern Minnesota (R. Timm's work in Cook County from 1971-1973 representing the only extensive and intensive recent survey in the region). Although several authors have described rock vole habitats in Minnesota and elsewhere, we lack good understanding of habitat selection by this species (specifically, the extent to which rock voles are very narrow habitat specialists). Further data on these problems are necessary for 1) a better understanding of the status and biology of this species in the state and 2) ascertaining whether management/protection of rock vole habitats is desirable to assure its survival in Minnesota.
This report describes field research designed to examine the above problems. Specifically, this work was directed towards locating as many new populations of this species as possible and, in conjunction, assessing the variety of habitats represented by new localities. This work was conducted in Cook County during summer and fall 1982, and was supported by funds provided by the Minnesota Department of Natural Resources Nongame Program. Maps for use in the field work were provided by the USDA Forest Service, and Forest Service personnel provided valuable suggestions on potential sampling localities.