Small Mammal Inventory of the Apostle Islands National Lakeshore and St. Croix National Scenic Riverway

Smith, Gus; Fawver, Emily

Island colonization by mammals is a function of island distance from source populations, island size, and the impedance through which mammals must travel to reach the islands. We inventoried small mammals at the Apostle Islands National Lakeshore, an archipelago of 22 islands in Lake Superior, and at the Saint Croix National Scenic Riverway, where islands were represented by isolated prairie patches surrounded by a forest matrix. At the Apostle Islands, trapping was conducted at thirteen locations on five islands and spanning 1,814 trap nights. At the Saint Croix Riverway, trapping was conducted at four locations encompassing 664 trap nights. All mammals were live trapped, tagged, and released. Four species were captured at the Apostle Islands with the southern red-backed vole the most abundant small mammal captured on all islands. At the Saint Croix Riverway, six species were captured including the meadow vole, the only species captured at both Parks. The other species included three mouse species, eastern chipmunk, and thirteen-lined ground squirrel. At the Apostle Islands, the combination of an island’s distance from a source population coupled with the island’s size appears to limit colonization. At the Saint Croix Riverway, prairie generalists were located, although no prairie obligates were captured, suggesting that colonization may be limited by the landscape matrix.