Habitat use by the southern red-backed vole (Clethrionomys gapperi) : response of an old-growth associated species to succession

I examined populations of the southern red-backed vole ( Clethrionomys gappen) and deer mouse (Peromyscus maniculatus) in 4 successional stages (65, 138, 256, 457 Y) in cedar-hemlock (Thuja plicata-Tsuga heterophylla) forests of Glacier National Park to determine macrohabitat selection among stands and microhabitat selection within stands. Abundance of Clethrionomys gapperi and Peromyscus maniculatus increased with increasing stand age. Microhabitat use differed from available habitat for both species within most age classes, but was not consistent for either species among age classes. The inconsistency in microhabitat use among successional stages and lack of correspondence between micro- and macrohabitat variables selected leads to the conclusion that macrohabitat associations determine microhabitat selection. In order to properly assess habitat use at either scale the difference between scales must be addressed in the design and analysis of habitat studies. Peromyscus maniculatus behaved as a generalist at the macrohabitat scale, but exhibited stronger microhabitat selection than did C. gapperi. I suggest that P. maniculatus may exhibit habitat switching and respond to local site conditions by developing search images that manifest themselves as distinctive foraging patterns at the microhabitat scale. Such behavior would render P. maniculatus a potentially formidable competitor for resources and explain its tenacity for a wide variety of habitats. Clethrionomys gapperi exhibits a strong positive linear relationship with stand age and old-growth conditions near the forest floor. If monitored in conjunction with other species such as the pine marten (Martes americana), pileated woodpecker (Dryocopus pileatus) and barred owl (Strix asio), C. gapperi could contribute significantly to an indicator guild for identifying and monitoring the old-growth condition. I also compared fluorescent pigment tracking and live trapping to determine microhabitat use by Clethrionomys gapperi. The two methods generally agreed, but fluorescent pigment tracking may allow more sensitive analyses of microhabitat use