Habitat, Abundance, and Distribution of Six Species of Shrews in Manitoba

Abstract

Habitat selection, abundance, and distribution of Sorex cinereus, S. arcticus, S. monticolus, S. palustris, Microsorex hoyi , and Blarina brevicauda in Manitoba are described. Manitoba covers six terrestrial biotic zones ranging from the Arctic Tundra Biome to the Grassland Biome. During 9 years of study, a total of 1,762 specimens was obtained from about 1,000 sites categorized into 30 hydric, mesic, and xeric habitats. Shrews also were censused on 28 2-ha quadrats representing all the major plant communities. Present distributions of the six shrews are interpreted in light of the advances and retreats of glaciers, glacial lakes, and biomes since the Wisconsin maximum. Range extensions are reported for Microsorex, S. palustris, S. arcticus , and S. monticolus . S. monticolus occurs across Canada in the taiga as far east as Thompson, an enormous region from which it was previously unknown. These four species have glacial-relict populations along the southern treeline, and the first three are also limited in distribution by the northern treeline. S. cinereus was the most widespread and abundant shrew (70.1% of captures); Blarina, S. arcticus , and S. palustris were common (11.2, 9.5, and 7.4% respectively); and Microsorex and S. monticolus were rare (1.1 and 0.7%). The most productive habitats for shrews were grass-sedge marsh and willow-alder fen, the only two in which all six species were found. Types of vegetation and cover influenced the distribution and abundance of shrews through the maintenance of high moisture levels and the provision of food supplies.