The California vole, Microtus californicus, is a small rodent species found across a significant portion of California and parts of southwestern Oregon. These animals are often mistakenly called “California meadow mice” but are distinct from true mice. They are a common component of many Californian ecosystems.
Physical Description and Habitat
California voles vary in size by geographic location, with southern subspecies generally larger than their northern counterparts. They measure 139 to 207 millimeters (5.5 to 8.1 inches) in total length, with tails 39 to 68 millimeters (1.5 to 2.7 inches). Males are slightly larger than females, about six percent longer and eleven percent heavier. Their fur color ranges from buffy brown to grayish brown or dark brown on top, often with a reddish tint along their back, while their underside is blue-gray to white, and their tails are bi-colored.
These voles inhabit a variety of environments along the Pacific Coast, from central Oregon down to northern Baja California. They are commonly found in grasslands, broad-leaved chaparral, and oak woodlands. They prefer areas with dense vegetation, including marshy ground, wet meadows, and coastal wetlands. Despite their preference for moist areas, they can also be found in drier, grassy hillsides.
Diet and Daily Activities
California voles are primarily herbivores, consuming grasses, sedges, and other green leafy plants. Seeds and roots become more prominent in their diet during summer or when other plant foods are scarce. Occasionally, they may supplement their diet with bird eggs or other protein sources.
These voles are active year-round and do not hibernate or store large quantities of food. Their activity peaks around dawn and dusk, a pattern known as crepuscular activity, with short bursts of movement every few hours. A clear sign of their presence is the network of narrow runways they create through dense grass and groundcover, connecting their shallow burrows. These runways, 1.5 to 2 inches in diameter, lead to multiple burrow openings and are often hidden beneath vegetation, providing safe pathways to their underground shelters.
Unique Social Structure and Reproduction
California voles are social, often living in groups that include a single male, one or more females, and their young. While considered monogamous, forming pairs that mate for life, males may breed with multiple females, especially in dense populations or those with unbalanced sex ratios. Breeding can occur year-round in coastal areas, but in non-coastal regions, it peaks during the wet season, from March to April.
Reproduction in California voles involves induced ovulation, triggered by copulation. Females experience a post-partum estrus, allowing them to breed again within 15 hours of giving birth, resulting in four to five litters per season. The gestation period is 22 days, with litter sizes ranging from one to eleven young, averaging four to five offspring.
Both parents share parental duties, with the male sometimes assisting in nest construction. Young voles are born altricial—helpless, blind, and hairless—weighing 2.5 to 2.8 grams. They develop fur within five days and open their eyes around nine days, becoming weaned and independent at two weeks of age. Females reach reproductive maturity as early as three weeks old, while males mature around five to six weeks.