Common to abundant in valley foothill and montane riparian habitats, aspen, and lacustrine, riverine, and estuarine habitats. Also occupies human-made habitats such as roadside and irrigation ditches. Young also may be born in coot or diving duck nests. Permanent water bordered by aquatic vegetation. Diurnal and nocturnal.
Rainfall stimulates earlier activity and increased individual movements.
Territorial aggression increases with reproductive activity. Much individual, seasonal, and geographic variation in aggressive behavior. Breeds year-round, weather permitting, in southern part of the state. In northern counties, reproduction is confined to spring and summer, peaking from April to June. Fewer litters and smaller litter sizes are typical in marginal habitat.