MOBILITY AND HABITAT UTILIZATION OF SMALL MUSTELIDS IN RELATION TO CYCLICALLY FLUCTUATING PREY ABUNDANCES

Abstract

We examined the winter season mobility and habitat utilization of two mustelid predators, the least weasel (Mustela n. nivalis) and the stoat (M. erminea) in western Finland. Cyclically fluctuating abundances of voles offered an opportunity to compare speciesspecific behavioral adjustments to the density of main prey. Daily lengths of small mustelid snowtracks in different habitats were recorded during six successive winters covering two three-year population cycles of voles (field vole Microtus agrestis, sibling vole M. rossiaemeridionalis and bank vole Clethrionomys glareolus). Tracks of least weasels were longest in the low phase of the vole cycle indicating that least weasels as Microtus vole specialists increased mobility in searching for prey at low densities of voles. The mobility of stoats was highest in the early decline phase. Both small mustelid species preferred farmland habitats typical for Microtus species, in particular at high densities of voles. Stoats as semi-generalist predators may shift to alternative prey leading to changes in habitat utilization, when voles are decreased to low densities. This was observed when stoats utilized woodland habitats more in the low than in other phases of the vole cycle.