Voles (Microtus spp.) occupy perennial grasslands and agricultural areas in many parts of North America. This study was designed to provide a detailed analysis of the population dynamics of montane voles (M. montanus) in old field and orchard habitats. Vole populations were intensively live-trapped in replicate old field and orchard sites over a 4-year period (1982-86) at Summerland, British Columbia, Canada. Populations of montane voles reached peak densities of 186 and 144 voles/ha in old field sites before declining to numbers averaging less than 60 voles/ha. Orchard populations of montane voles also followed this pattern but at consistently lower numbers than old field sites. This difference in abundance ranged from 2.3-3.6 times during the peak year to 23.8-116.3 times in the decline year, at which time montane voles had declined to a mean number of 0.3-2.4 voles/ha in orchard sites. Length of breeding seasons, proportion of reproductive voles, and mean number of recruits were generally similar in old field and orchard sites. Overall mean survival of voles tended to decline through time in orchard sites, averaging 0.47 compared with old field survival of 0.76. Mean body mass of voles was consistently higher in old field than orchard sites. Montane vole populations in orchards seemed to be linked to source area dynamics of populations in old fields
