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Microtus californicusCalifornia vole

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, Jr., 1998; Wilson and Ruff, 1999)

Physical Description

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)

  • Sexual Dimorphism
  • male larger
  • Range mass
    38 to 108 g
    1.34 to 3.81 oz
  • Range length
    139 to 214 mm
    5.47 to 8.43 in

Reproduction

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)

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 Mediterranean, 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 species 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)

  • Breeding interval
    These voles can breed every three weeks under good conditions.
  • Breeding season
    The breeding season seems to heavily rely on the wet season in non-coastal parts of California. In coastal populations, breeding is aseasonal.
  • Range number of offspring
    1 to 11
  • Range gestation period
    22 (high) days
  • Average weaning age
    2 weeks
  • Average time to independence
    2 weeks
  • Range age at sexual or reproductive maturity (female)
    21 (low) days
  • Range age at sexual or reproductive maturity (male)
    25 to 42 days

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)

  • Typical lifespan
    Status: wild
    1 to 12 months

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)

  • Range territory size
    80 to 125 m^2

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)

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, Jr., 1998)

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)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit

Predation

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, February 2, 1995; Whitaker, 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)

Commensal/Parasitic 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: 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.

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)

  • Negative Impacts
  • crop pest

Conservation 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.

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

Nancy Shefferly (editor), Animal Diversity Web.

Lisa Peronne (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

coprophage

an animal that mainly eats the dung of other animals

crepuscular

active at dawn and dusk

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

marsh

marshes are wetland areas often dominated by grasses and reeds.

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

Burt, W., R. Grossenheider. 1980. Peterson Field Guide: Mammals. New York: Houghton Mifflin Co..

Gee, H. February 2, 1995. In the eye of the kestrel. Nature, 373: 387.

Ingles, L. 1965. Mammals of the Pacific States (CA, OR, WA). Stanford California: Stanford University Press.

Krohne, D. 1982. The Bases of Intra- and Interpopulational Reproductive Variation and their Demographic Consequences in the California Vole. Ann Arbor, Michigan: University Microfilms International.

Tamarin, R. 1985. Biology of New World Microtus. Shippensburg, Pennsylvania: Special Publication No.8 American Society of Mammalogists.

Tamarin, R., R. Ostfeld, S. Pugh, G. Bujalska. 1990. Social Systems and Population Cycles in Voles. Boston: Birkhauser Verlag.

Whitaker, Jr., J. 1998. National Audobon Society, Field Guide to Mammals. New York: Chanticleer Press.

Wilson, D., S. Ruff. 1999. The Smithsonian book of North American mammals. Washington, D.C.: Smithsonian Institution Press.

Zim, H., D. Hoffmeister. 1955. Golden Guide: Mammals. New York: Golden Press.

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