Microtus population biology: demography of M. oregoni in southwestern British Columbia

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Abstract
Populations of M. oregoni were livetrapped from 1971-1974 in old field and grassland habitats at the University of British Columbia [B.C.] Research Forest, Maple Ridge, [B.C.] Forest (1974-1978), and shrub (1975-1980) habitats were also sampled intensively. An additional population was livetrapped (1971-1974) in abandoned grassland near Ladner, B.C. M. oregoni exhibited a 3-4 yr cyclic fluctuation in abundance in the old field and shrub habitats. Maximum density (72 voles/ha) was recorded on the old field grid which was optimum habitat for this species. Winter breeding and a long reproductive period prior to the peak year, and larger body size during the peak than other phases of the cycle were characteristic features of the old field population. This vole species did not have a multiannual cycle in habitats where the competitor, M. townsendii was present. Oregon voles were 3-4 g heavier at the Research Forest than at the Ladner study area. Female voles were more prevalent than males in all populations.