"California Mice are nocturnal, with peak activity periods near dusk and dawn. Adults are fairly sedentary, spending much of their time nesting under fallen logs or debris, in trees, or in the dens made by other rodents. The social organization is monogamous, with males and females forming long-term relationships—""long term"" being a relative term, since this species has a life span of 9-18 months. Males help care for the young, and the male's presence increases their chance of survival. Females nurse their young for a prolonged period, compared to other Peromyscus; the young are not weaned until they are about five weeks of age. Female offspring disperse farther than males to establish their adult territories, another unusual characteristic."

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Restricted to southern California (United States) and northern Baja California (Mexico). Elevational range sea level to 2,440 m.

Peromyscus californicus is found from San Francisco Bay south and east along the coast ranges and in the eastern Sierra Nevada from Mariposa Co. south to Kern Co. in California south to Bahia San Quintin on the Pacific coast of northwestern Baja California (Bryiski and Harris, 1984; Alvarez-Casteñada and Cortés-Calva, 1999).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: San Francisco Bay region and central Sierra Nevada foothills south, west of the Mohave Desert and not including the San Joaquin Valley, to northern Baja California (see map in Carleton 1989).

Peromyscus californicus is the largest species in its genus. Its total length is between 220-285 mm, with tail length ranging from approximately 117-156 mm (Whitaker 1997). It is distinctly bicolored. Adults have a yellowish brown or gray mixed with black dorsal coloring, and a white underside, and feet. Many individuals have a distinctly fulvous throat patch and a fulvous lateral line separating dorsal from ventral pelage in the shoulder region, sometimes extending to the thigh. Juveniles are gray on top with a white underside. The tail matches the dorsal pelage and is not sharply bicolored. The ears are large, ranging from 20-25 mm (Whitaker 1997).

Range mass: 33.2 to 54.4 g.

Range length: 220 to 285 mm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Average basal metabolic rate: 0.267 W.

Length: 29 cm

Weight: 54 grams

Sexual Dimorphism: None

Length:
Range: 220-285 mm

Weight:
Range: 33.2-54.4 g

Habitat and Ecology

Systems

• Terrestrial

Peromyscus californicus is generally restricted to dense chaparrel and broad-sclerophyll woodland (Meritt 1974). The limiting factor for its small geographic range may be the need for naturally occurring burrow holes of the proper size for these larger animals (Grinnell and Orr 1934), as they are poor natural burrowers. The co-occurrence of woodrat houses and a distributional association with the California laurel complex have also been noted as potential limiting factors (Meritt 1974), although there is no direct evidence to implicate any of these.

Range elevation: 2440 (high) m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: chaparral ; forest

Comments: Chaparral and foothill oak woodland, Upper Sonoran life zone, moist laurel and redwood forests (Merritt, in Wilson and Ruff 1999). Finds cover in natural holes and crevices and uses burrows of other animals. Often lives in stick nests built by wood rats. Young are born in complex nests of grasses, weeds and sticks located under logs or other debris.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Peromyscus californicus specializes on the fruits, seeds and flowers of shrubs (Meserve 1976). In woodland habitat the seeds of California bay laurel (Umbellularia californica) are the major food (Meritt 1974). Arthropods may make up a small percentage on the diet but these are not actively hunted (Meserve 1976). Water is most likely obtained from the food that it eats and supplimented with dew; P. californicus is not as good at water conservation as other species in the genus (Meritt 1974).

Animal Foods: insects

Plant Foods: leaves; seeds, grains, and nuts; fruit; flowers

Primary Diet: herbivore (Frugivore , Granivore )

Comments: Shrub fruits, seeds, and flowers. Other foods sometimes eaten include grasses, forbs, fungi, and arthropods. Often associated with bay (Umbellularia californica), may feed on its seeds.

California mice are important seed predators in the ecosystems in which they live and they form an important prey base for rattlesnakes, owls, and other predators.

California mice, like other Peromyscus species, are an important prey base for many predators throughout their range. They are preyed on by hawks, owls, rattlesnakes, and small mammalian predators. Their nocturnal and secretive habits help to protect them from many predators.

Known Predators:

• western rattlesnakes (Crotalus oreganus)
• barn owls (Tyto alba)

Anti-predator Adaptations: cryptic

More territorial than P. MANICULATUS; nest site defended by both males and females. Density estimates vary with habit (Merritt 1978). Life expectancy in field 9-18 months. In Monterey County, females dispersed farther than did males; females up to 790 m (mean 155), males up to 450 m (mean 70) (Ribble 1992).

Like other Peromyscus species, California mice have keen vision and hearing and use chemical cues extensively in communication.

Communication Channels: visual ; chemical

Perception Channels: visual ; acoustic

Comments: Active throughout the year; primarily nocturnal.

California mice generally live for 9 to 18 months. Populations tend to be fairly stable and at low densities, as compared to other Peromyscus species.

Typical lifespan

Status: wild: 9 to 18 months.

Average lifespan

Status: captivity: 5.5 years.

Maximum longevity: 5.5 years (captivity) Observations: One specimen lived 5.5 years in captivity until it escapted (Richard Weigl 2005).

Unlike most mice P. californicus is truly monogamous, and once mated will stay paired for life (McCade and Blanchard 1950; Ribble 1991; Ribble and Salvioni 1990; Guvernick and Nelson 1990).

Mating System: monogamous

Mating may occur year round, but mainly from March to September. In the lab P. californicus can have up to 6 litters per year, but in the wild the average is 3-4. Gestation is 30 to 33 days and average litter size is 2 (from 1 to 3), with a slight increase in litter size with the age of the female. Compared to other species of Peromyscus, P. californicus young are rather precocious, although weaning is not completed for about 5 weeks. They also have a long period before reaching sexual maturity, approximately 11 weeks for females and even longer for males.

Breeding interval: Females can have up to 6 litters per year, but 3 to 4 is more typical.

Breeding season: Breeding can occur year round but most breeding occurs from March to September.

Range number of offspring: 1 to 3.

Range gestation period: 30 to 33 days.

Average weaning age: 5 weeks.

Average age at sexual or reproductive maturity (female): 11 weeks.

Range age at sexual or reproductive maturity (male): 11 (low) weeks.

Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 4.46 g.

Average number of offspring: 2.

Average age at sexual or reproductive maturity (female)

Sex: female: 46 days.

Males help extensively in caring for and protecting the young.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)

In Monterey County, breeds throughout most of the year (mainly December-May), with few pregnant or lactating females present from mid-summer until onset of fall or winter rains (Ribble 1992). Average of 2-3 litters/female/year. in central California. Gestation 31-33 days in nonlactating females (extended several days in lactating females due to delayed implantation); gestation also reported as averaging 23-24 days in nonlactating females (see Kirkland and Layne 1989); mean age of first estrus 44 days (Gubernick 1988). Litter size 1-3 (usually 2). Interbirth interval 1-3 months within single breeding season. Average of 4 young/female/season. Persistent association between paired male and female; male displays extensive parental care; monogamous. See Ribble (1992) for further details.

Despite its relatively narrow habitat, limited geographic range, and generally low population densities, Peromyscus californicus populations remain healthy.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

Like other members of Peromyscus, California mice fecal matter may transmit hantavirus.

Negative Impacts: injures humans (carries human disease)

Comments: Smith (1979) examined morphological and electrophoretic variation and retained only two subspecies, californicus in the north and insignis in the south.