Population Dynamics of Small Mammals in Farmstead Shelterbelts

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Abstract
Various aspects of the population dynamics of Sorex cinereus, Blarina brevicauda, Clethrionomys gapperi, Microtus pennsylvanicus, and Peromyscus leucopus were studied for 27 months in Minnesota farmstead shelterbelts. Total numbers of individuals of all species combined were greatest in summer and autumn; species-specific peaks in seasonal abundance were partially attributed to juvenile recruitment. Percentages of breeding adult females were similar in the three species of cricetids, but relatively fewer adult males of M. pennsylvanicus were in reproductive condition than in other cricetids. Young cricetids tended to be transient compared to adults; in P. leucopus, young females were more likely to be residents than young males. Adult transients weighed less than adult residents in both M. pennsylvanicus and P. leucopus. Distances moved within shelterbelts did not vary among species; movements between shelterbelts occurred most often in B. brevicauda but never in P. leucopus. Probabilities of recapture over months were comparable among species. Aspects of the population dynamics of the five species in these man-made habitats generally were similar to those reported by studies in less modified environments. Because of the importance of shelterbelts to populations of C. gapperi and P. leucopus and to other species of wildlife, efforts should be made to preserve these wooded islands in intensely-farmed regions of the Upper Midwest.