The range of California bats extends from southeastern Alaska, through the western United States, south to southern Mexico. In Canada they are confined to British Columbia, including coastal Vancouver Island and Queen Charlotte Islands (Nagorsen and Brigham 1993).

Biogeographic Regions: nearctic (Native )

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

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Western North America, from extreme southern Alaska south through British Columbia and western U.S. to southern Baja California and Guatemala (Koopman, in Wilson and Reeder 1993). In U.S. found throughout desert Southwest, and in lowlands to Montana, Utah, and Colorado. Winters in California, Nevada, Utah, Arizona, and Texas; full extent of winter range not known (Barbour and Davis 1969). To elevations of 6000 ft.

California bats measure 70-94 mm in total length, with a forearm length of 30-35 mm, making them one of the smallest Myotis species in North America. The fur is long and dull, not glossy, and shows great geographic variation in colour, ranging from rusty reddish-brown to rich-dark chestnut brown. In high-altitude populations of M. californicus a darker pelage prevails. Where it is found in arid areas the fur is typically pale yellowish-orange. In areas of low elevation, the bat is especially small in size and pale in colour, while in the forests of the Pacific Northwest and the forested highlands of Mexico, it is darker in colour. There is no distinct sexual dimorphism in this species, although females are, on average, larger than males in most comparisons. The ears, wings and tail membranes are black. The ears are relatively long and extend beyond the nose when pushed forward. The hind foot is small, less than half the length of the tibia (6-9 mm). The dental formula is 2/3 1/1 3/3 3/3 = 38. The calcar is slender and prominently keeled, and the skull is delicate, characterized by a steeply sloping forehead. Northern individuals have been found to have smaller skull dimensions than those in the south (Banfield 1974; Nagorsen and Brigham 1993; Simpson 1993; Wilson and Ruff 1999).

Range mass: 3.3 to 5.4 g.

Length: 9 cm

• Terrestrial

California bats have a wide tolerance of habitat including semi-arid desert regions of the Southwest, arid grasslands, forested regions of the Pacific Northwest, humid coastal forests and montane forests (Banfield 1974; Nagorsen and Brigham 1993).

Terrestrial Biomes: desert or dune ; forest ; mountains

Comments: Western lowlands; sea coast to desert, oak-juniper, canyons, riparian woodlands, desert scrub, and grasslands. Often uses man-made structures for night roosts. Uses crevices of various kinds, including those in buildings, for summer day roosts. May roost also on small desert shrubs or on the ground (see Simpson 1993). Hibernates in caves, mines, tunnels, or buildings. May form small maternity colonies in rock crevices, under bark, or under eaves of buildings.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

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.

California bats are insectivorous, feeding mainly on flies, moths and beetles. They forage only on insects in flight and are slow, acrobatic flyers, detecting prey at close range (less than 1 meter) and using echolocation calls during approach. Specific diet remains constant throughout the year, but likely varies from area to area. In British Columbia, M. californicus has been observed feeding mainly on Trichoptera and some Coleoptera, while further south, in Oregon, consumption consists primarily of Lepidoptera and Diptera (Banfield 1974; Fenton and Bell 1979; Simpson 1993; Wilson and Ruff 1999).

Comments: Insectivorous. Forages with a slow erratic flight pattern within approximately 5-10 feet of the ground. Forages along margins of tree clumps, around edge of tree canopy, over water, and well above ground in open country (see Simpson 1993).

In summer, roosts alone or in small groups (Simpson 1993).

Comments: Most active in early evening; begins foraging shortly after sunset; second peak in activity may occur after midnight, after initial activity and subsequent rest period; activity may be curtailed and unimodal in cool weather (see Simpson 1991). Known to hibernate in U.S. during winter, but also known to be active in winter. In southern California occasional individuals have been found active on warm winter days. Active bats regularly have been caught in Nevada in fall and winter, frequently in temperatures below 43 F.

There is little documented information available on reproduction and ontongeny in M. californicus. It is known that mating occurs in autumn. Females store sperm in the uterus and fertilization follows ovulation in the spring. In California mating also may occur in the spring. A single young is born in late June or early July. The young develop rapidly and can fly about one month after birth. California bats have a potential reproductive lifespan of 15 years (Nagorsen and Brigham 1993; Simpson 1993; Wilson and Ruff 1999).

Range number of offspring: 1 to 1.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; sperm-storing

Breeds in late fall in most of range, or early spring in California. Females give birth to single young, late May to mid-June (Barbour and Davis 1969), in July in Canada (Banfield 1974; van Zyll de Jong 1985). In southwestern California, no pregnant females were found after mid-June. One young per year. Potential reproductive lifespan of 15 years. Colonies usually are small, up to about 25 individuals.

The status of the California bat is common (CITES 2000; IUCN Species Survival Commission 2000; USFWS 2000).

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Myotis californicus mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

California bats may cause disturbance by their use of man-made shelters as roosts. In addition, the presence of rabies has been detected in specimens, although not at significant levels (Banfield 1974).

Through its consumption of insects, California bats play an important role in ecological balance and crop pest population control (Banfield 1974).

Comments: A phylogenetic study based on mtDNA sequence divergence data did not recover distinct lineages of M. californicus and M. ciliolabrum as recognized by morphology (i.e., analysis of molecular data failed to support the hypothesis that M. californicus and M. ciliolabrum are monophyletic species (Rodriguez and Ammerman 2004). These results suggest that (1) M. californicus and M. ciliolabrum have recently diverged or (2) they are one phenotypically variable species. Additionally, M. leibii was included within clades containing both M. californicus and M. ciliolabrum (Rodriguez and Ammerman 2004). Further data from M. leibii are necessary to validate its phylogenetic relationship to M. ciliolabrum and M. californicus (Rodriguez and Ammerman 2004). Comparisons among outgroups (M. yumanensis, M. lucifugus, and M. evotis) found sufficient support for specific status of M. leibii, but sequence divergence between M. evotis and the leibii group was small (2.9%) and within the intraspecific range. Further sampling of M. evotis is necessary to establish the level of divergence between M. evotis, as well as other long-eared Myotis, and the leibii group (Rodriguez and Ammerman 2004).

See Bogan (1975) for information on geographic variation and subspecies in the southwestern U.S. and Mexico. Simmons (in Wilslon and Reeder 2005) stated that subspecies are poorly delimited.