By Lisa Peronne
Geographic Range
Microtus californicus occurs along the Pacific Coast of North America, from central Oregon southward to northern Baja California. It occurs in the woodlands, shrublands and grasslands of these areas. (Tamarin, 1985)
Habitat
California voles inhabit areas of broad-leaved chaparral, oak woodlands, and grasslands along the Pacific Coast in northern Baja California to central Oregon. This species has a restricted distribution, which is possibly due to relic populations. It seems to utilize unusual habitats in California compared to other species of voles throughout the North American continent. Marshy ground, saltwater and freshwater locations, wet meadows, coastal wetlands and dry, grassy hillsides are the preferred macrohabitats of this species.
California voles are semifossorial. Their microhabitat consists of burrows, grass runways, and earth tunnels where piles of grass cuttings and fresh vegetation are often found. Piles of feces are also found in the runways. (Burt and Grossenheider, 1980; Whitaker and Jr., 1998; Wilson and Ruff, 1999)
These animals are found in the following types of habitat:
temperate 
; terrestrial .
Terrestrial Biomes:
desert or dune ; savanna or grassland ; chaparral .
Wetlands: marsh .
Other:
agricultural ; riparian .
Physical Description
(1.34 to 3.8 oz)
(5.47 to 8.43 in)
M. californicus present a lot of variation in size depending upon where they are found. Subspecies found in the south of the species range can be much larger than those found in the north.
In northern California, the total length veries between 139 ans 207 mm, of which only 39 to 68 mm is contributed by the tail. Males weigh between 33 and 81 g, averaging 52 g, and females can weigh between 30 and 68 g, averaging 47 g.
California voles are sexually dimorphic with the males being six percent longer and eleven percent heavier than females.
The coat of these animals is buffy brown, grayish brown or dark brown (blackish toward coast, reddish in desert) colored on top, with a reddish tinge down the middle of the back. The underside is blue-gray to white. The tail is bi-colored. The feet are pale, and the eyes are dark brown to black. M. californicus has 8 mammae.
This species can be distinguished from other voles by the following characteristics:
Microtus montanus occurs at higher elevations;
M. longicaudus is longer and its tail more bicolored;
M. townsendii has different cranial and dental features; and
M. oregoni is smaller and has only 5 toe pads. (Burt and Grossenheider, 1980; Ingles, 1965; Wilson and Ruff, 1999)
Some key physical features:
endothermic ; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
These voles can breed every three weeks under good conditions.
The breeding season seems to heavily rely on the wet season in non-coastal parts of California. In coastal populations, breeding is aseasonal.
California voles seem mostly monogomous when populations aren't too dense. Dense populations or populations with unbalanced sex ratios will display polygynous traits. In these populations, males defend territories where grass is the staple diet, and females defend areas where fruits and forbs are the primary food source.
When polygyny is the prevailing mating system, females tend to have neighboring territories with their sisters and dispersing males may have little or no contact with close relatives.
Suppression of sexual maturation on the natal home range by the presence of the mother occurs. Kin recognition has little influence on inhibiting inbreeding, even in monogamous populations.
Adult males will cannibalize young that are not theirs. Females will also abort their litters if exposed to the phermones produced by unfamiliar males. (Ingles, 1965; Tamarin, 1985; Tamarin et al., 1990; Wilson and Ruff, 1999)
Mating systems:
monogamous ; polygynous .
Ovulation in M. californicus is induced by copulation. This species experiences a post-partum estrus, and breeding can occur within fifteen hours after young are born. This allows up to 4 or 5 litters a season.
The breeding season is somewhat variable throughout the range of this species. Germination of annual grasses in the fall seems to initiate reproduction in some popultions. In other populations, where the climate is very mediteranean, reproduction begins near the time of the first rains, and ends when the hot summer dries out the vegetation. In coastal populations, where the grasses stay green all year, and temperatures are mild, breeding can occur thorughout the year.
The gestation is twenty-two days. LItters of 1 to 11 young can be roduced, but the average is 4 or 5 young. Perennial grassland populations average about two embryos less than those in annual and mixed annual-perennial grassland populations. Young are altricial and weigh approximately 2.5g at birth. The pups are quickly weaned at two weeks old.
Females reach reproductive maturity by three weeks old, and the male at five weeks. Under some conditions, males can mature more rapidly, reaching sexual maturity by about 25 days of age. Sexual maturity can be supressed by the presence of the parents on the natal range. This allows the species to rapidly colonize when population densities are low, but to limit reproduction somewhat when populations are very dense.
Microtus sp., in general, appear to have a fairly plastic reproductive biology where the emphasis seems to be on the ability to produce the correct response (phenotypic) given the ecological conditions in which the population finds itself. Populations experience cyclic and annual fluctuations. The population typically grows for three to four years then declines rapidly in mild, temperate areas. In strongly seasonal habitats, the growth phase is two to five years. (Ingles, 1965; Krohne, 1982; Tamarin, 1985; Tamarin et al., 1990; Wilson and Ruff, 1999)
Key reproductive features:
iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; induced ovulation ; fertilization (internal ); viviparous ; post-partum estrous.
As in all mammals, the female provides the young with milk for the duration of nursing. Although the young are altricial at birth, they grow quickly. Weaning occurs when the young are abut two weeks old.
In polygynous systems, females are the primary care givers, with neighboring territories being occupied by their sisters. In monogamous systems, males will participate in brood care. In these mating systems, males participate in parental care by gathering nesting materials and retreiving nestlings. Both males and females will display territorial traits, which helps to protect the young from intruders.
Nests are made with dried grasses and forbs and are located under logs or boards or under the earth's surface a few centimeters. (Tamarin et al., 1990; Wilson and Ruff, 1999)
Parental investment:
altricial ; pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: male, female).
Lifespan/Longevity
A successful lifespan for a vole will be up to a year, but the average lifespan is only a few months. (Wilson and Ruff, 1999)
Behavior
M californicus is most active near dawn and dusk with short bursts of activity every few hours in between. Their crepuscular pattern is most obvious during the long, hot, dry days of summer. These animals are actove throughout the year. They have no hibernation and are not known to store food. California voles are a social species. Their runways are interconnecting, but individuals are territorial, especially during the breeding season. (Wilson and Ruff, 1999)
Home Range
Adult males have larger home ranges (125 sq meters) than females (80 sq meters), but their core area (where they spend 85% of their time) is about the same. (Wilson and Ruff, 1999)
Key behaviors:
crepuscular ; motile ; sedentary ; territorial ; social .
Communication and Perception
California voles communicate mostly through scent by depositing urine in areas of its runways as a tracking device. This tells the vole where it has been and who else inhabits a runway. Squeaks are also heard from adults during distress and young when communicating to the parent(s).
As with most other mammals, there is likely some visual communication as well. (Whitaker and Jr., 1998)
Other communication keywords:
scent marks .
Food Habits
M. californicus is herbvivorous and eat mostly grasses and roots, but also relies on sedges, fruits and forbs in certain areas. In the winter, the vole eats mostly roots and underground plant parts. Grain will also be eaten when available. (Burt and Grossenheider, 1980; Ingles, 1965)
Primary Diet:
herbivore (folivore , frugivore , granivore ); coprophage .
Plant Foods:
leaves; seeds, grains, and nuts; fruit.
Predation
- American kestrels (Falco sparverius)
- harrier hawks (Circus)
- white-tailed kites (Elanus leucurus)
- red-tailed hawks (Buteo jamaicensis)
- Barn owls (Tyto alba)
- great horned owls (Bubo virginianus)
- long-tailed weasels (Mustela frenata)
- ermine (Mustela ermina)
- coyotes (Canis latrans)
- gray foxes (Urocyon cinereoargenteus)
- snakes (Serpentes)
- herons (Ardeidae)
- egrets (Ardeidae)
- feral cats (Felis silvestris)
Voles spend as little time exposed to the surface as possible. Underground tunnels are commonly used as are runways throughout tall grasslands. Unfortunately for the voles, the urine they use to communicate to each other is the way their diurnial predators track them and determine vole density. Through the raptors ability to see ultraviolet light, the florescent urine shows up in the runways and directs the predator to the prey's location. This could also explain how raptors are able to locate their vole prey even after population crashes.
There are a great number of vole predators, including coyotes, kestrels, hawks, weasles, kits, owls, snakes, herons, egrets, and ferrel cats. Because of their rapid reproduction and periody high population densities, these voles are a keystone prey species. (Gee and February 2, 1995; Whitaker and Jr., 1998)
Ecosystem Roles
With their potential to reproduce rapidly, these voles are prey for many carnivore species. They form an important link in food webs. these voles also are hosts to many species of parasites. (Tamarin, 1985; Wilson and Ruff, 1999)
Key ways these animals impact their ecosystem:
keystone species .
- Cestodes
- Nematodes
- Dermacentor ticks
- Ixodes ticks
- Hoplopleura lice
- Polyplax lice
- Fleas of 24 different species are known to use these voles as hosts
Economic Importance for Humans: Negative
During peak population times, numbers of voles are said to exceed to the hundreds per acre, and up to a thousand per hectare, causing crop problems in areas where farms coincide with vole habitat. (Wilson and Ruff, 1999; Zim and Hoffmeister, 1955)
Ways that these animals might be a problem for humans:
crop pest.
Economic Importance for Humans: Positive
Although there is apparently no direct benefit of this species for humans, it should be noted that without this keystone species, many of the larger animals that people enjoy watching, such as hawks, kestrels, coyotes and foxes, would not be able to exist at such high densities, and therefore would be a much less visible part of local ecosystems.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Migratory Bird Act: [link]:
No special status.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
These voles are quite common and so are not a big conservation concern. Local abundances can vary from year to year, but overall the population cycle seems stable. However, because thes voles are so important to their ecosystem, it is worthwile to keep an eye on their population cycles and habitat availability, so that other species which depend upon them for food, and whose population status may be less secure, are safeguarded. (Wilson and Ruff, 1999)
Other Comments
Fossil Record: The size of the incisive foramina is used to help distinguish California voles from other species. In M. californicus, the foramina is wider and unconstricted, and the teeth are slightly larger than other species of vole that occur near California. It is possible M. californicus could have first appeared 1.8 million years before present in North America at the beginning of the Pleistocene, making it possibly one the first occurring in the *Microtus sp.
Humboldtian (Northwestern California), Diablian (Central California), Californian (Valley and Eastern California), and San Bernardinian (Southern California) provinces exist in California. There are seventeen subspecies of M. californicus that occur in its region. (Tamarin, 1985; Wilson and Ruff, 1999)
Contributors
Lisa Peronne (author), Humboldt State University.
Brian Arbogast (editor), Humboldt State University.
Nancy Shefferly (editor), Animal Diversity Web Staff.
