Rubbelke, D. 1984. Water shrews in Minnesota. Project summary prepared for the Minnesota Department of Natural Resources. 39 pp.
The purpose of this study was to gain a better understanding of the biology and distribution of the water shrew (Sorex palustris) and the methods by which water shrew populations can be estimated. In Minnesota, water shrews have been reported in 17 counties, primarily in the northern third of the state. The specific objectives of this study were to determine: (1) if the recorded distribution and abundance of Sorex palustris in Minnesota is complete; (2) the effectiveness of different trapping strategies for sampling water shrew populations; (3) the vegetative and physical characteristics of habitats occupied by S. palustris; and (4) the location of foraging for this species.
Three methods of trapping were used: saturation trapping, continuous-selective trapping, and water surface trapping (floating traps). Three different baits were used in each trapping regime: A "standard" mixture composed of peanut butter, rolled oats and baking grease; "anise" bait prepared by adding anise oil to the standard mixture for additional scent; "arthropod" bait prepared from a mixture of insects, arthropods, and earthworms homogenized in a blender. The baits were rotated during trap placement to insure an equal representation of baits at each trap position. Traps were set only in semi-aquatic to aquatic habitats.
Plants were collected and preserved as herbarium specimens and deposited in the College of St. Benedict/St. Johns University. 190 mammals representing at least 10 species were captured. Continuous-Selective trapping appears to be the most effective trapping strategy for all mammals when combined with careful placement of the traps. Water shrews did not appear to have a preference for any of the baits used in this study. All of the water shrews captured in this study occupied traps during overcast and/or rainy weather. Five of the seven specimens captured were within 15 cm of water. The remaining two specimens were trapped in tall grass adjacent to mud flats within 2 meters of the water.
This study demonstrated that water shrews: occur in wet marsh in central and northern Minnesota; occur in aquatic habitats in deciduous or coniferous forests; appear to be associated with moving streams bordered by a grass-sedge marsh that periodically floods and has occasional mud flats; appear to be associated with beaver activity; were most effectively trapped by continuous-selective trapping in undercut stream banks, along mud flats, etc.; typically occupy aquatic habitats and apparently forage in this area; hummocks formed by dense grasses such as P. arundinacea may provide cover/runways etc. necessary for activity; rainy weather appears to be a period for high activity; Meadow jumping mice (Z. hudsonicus) occupied every site in which they were trapped; Sorex cinereus and Peromyscus sp. may indicate a site unfavorable to water shrews.