ABSTRACT
The genera Peromyscus and Microtus are widely distributed throughout North America. Species diversity is greatest in the southern part of the continent for Peromyscus and opposite in temperate and northern regions for Microtus. Knowledge of general population changes is critical to accurate censuses of deer mice and voles. Populations of deer mice fluctuate seasonally, with low spring breeding densities and higher densities through the fall and winter. Both deer mice and voles are active year-round, although Peromyscus may enter a temporary period of torpor during particularly cold winters with little snow cover. Trappability of voles may be reduced when censusing high-density populations and during summer breeding periods.
