Habitat preferences of Clethrionomys rufocanus in boreal sweden

A long-term decline of vole populations in boreal Sweden, especially of the grey-sided vole (Clethrionomys rufocanus Sund.), has been revealed by snap-trapping in 1971-2004. We identified important habitats for the grey-sided vole by mapping the distribution of cumulated number of reproductive females in 1971-1978, prior to the major decline in the 1980s. Mean abundance of C. rufocanus was higher in the western (inland) than eastern (coastland) part of the study area. As the inland appeared to represent the most, as far as we know, pristine, abundant part of the population, we based identification of high quality habitats on inland data only. Four habitats were more important than others and yielded nearly 86% of the reproductive females in spring: (1) forests of dry, (2) moist and (3) wet/hydric dwarf-shrub type, in addition to (4) forest/swamp complexes rich in dwarf-shrubs. The latter three habitats were used more frequently than expected from their occurrence in the landscape. Still, the variation in density of reproductive females within patches of the same habitat was frequently high. This suggested that habitat composition in the surrounding landscape, perhaps may have affected local vole density at the patch scale. Clear-cut sampling plots appeared to be low-frequently used by reproductive females, but also by males and immatures. In conclusion, our study indicated the importance of also studying habitat at a larger scale than that of the patch to get a deeper understanding on how habitat influences local and regional densities and population dynamics of C. rufocanus.