ABSTRACT
Approximately 55 species of Microtus (including the previously separated subgenus Pitymys) live in North America and Eurasia. Microtus pennsylvanicus, the meadow vole, serves as the example for the genus. Most species of Microtus occupy habitats with dense grass, including wetlands; a few species occur in talus areas, forbs, forests, deserts, and agricultural fields. Microtus commonly make surface runways where the vegetation mat is dense. The few species that are semifossorial are also active above-ground. Microtus are generally active at all times of the day throughout the year; they are active under snow cover. Trap success can be expected throughout the year. Activity may decline on extremely hot days or on very cold nights, especially in habitats where the vegetation cover is sparse. Populations of many species of Microtus undergo cyclic fluctuations in abundance (at 2 to 5-year intervals); densities may range from less than one to several hundred per hectare during a population cycle. Home range diameters of individuals range from 20 to 50 m.
