Myotis californicusCalifornia myotis

Geographic Range

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).


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).

Physical Description

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
    0.12 to 0.19 oz


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


California bats roost alone or in small groups during the warmer months. They can be found in caves, mines, rocky hillsides, under tree bark, on shrubs, on the ground, and in buildings. Males and females roost separately during the warmer months. Females form small maternity colonies during pregnancy, birth, and lactation. During the winter months the sexes mingle and roost either solitarily or in small groups in caves, mines, and buildings. At high elevations and latitudes, they have been reported to hibernate in mines and caves during winter months, though they have been observed to be active for short time periods at temperatures below freezing, indicating that they occasionally emerge from torpor to feed. In forest populations, considerable switching of roosts has been documented, and a roost will seldom be re-used by the same bat once it has changed to a new one. As well, preference has been shown for specific species of tree, such as the ponderosa pine found in specific stages of decay and in relatively open areas. Though poorly investigated as of yet, this could have important implications for bat conservation. California bats are nocturnal, emerging to hunt just after sunset and foraging until dawn, with two peaks of hunting activity occuring between 10:00 and 11:00 pm and 1:00 and 2:00 am. Their feeding strategy involves locating a concentration of insects and capturing several in quick succession over a short distance. Their flight is slow and maneuverable, though erratic when pursuing prey. When hunting they have been observed making frequent abrupt alterations of flight path, invariably associated with feeding buzzes (high pulse repetition rates associated with pursuits of insects). There is no indication of territorial behavior when hunting, nor have they been observed hunting in groups. Little is known about mating behaviour and predator/anti-predator behaviour in M. californicus (Brigham et al. 1997; Fenton and Bell 1979; Nagorsen and Brigham 1993; Simpson 1993; Wilson and Ruff 1999).

Communication and Perception

Food Habits

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).

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

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).

Conservation Status

The status of the California bat is common (CITES 2000; IUCN Species Survival Commission 2000; USFWS 2000). (CITES, 2000; IUCN Species Survival Commission, 2000; U.S. Fish and Wildlife Service, 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. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Other Comments

Kidneys of California bats are adapted for water conservation in arid environments. Where this bat occurs in desert regions and arid interior basins, it utilizes small waterholes to obtain needed moisture (Wilson and Ruff 1999).


Liat Podolsky (author), University of Toronto.



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

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.


uses smells or other chemicals to communicate

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.


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.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

seasonal breeding

breeding is confined to a particular season


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


mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.


uses touch to communicate


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


Banfield, A. 1974. Mammals of Canada. Toronto, Canada: University of Toronto Press.

Brigham, R., M. Vonhof, R. Barclay, J. Gwilliam. 1997. Roosting behaviour and roost-site preferences of forest dwelling California bats (Myotis californicus). Journal of Mammalogy, 78 (4): 1231-1239.

CITES, 2000. "Convention on International Trade in Endangered Species of Wild Fauna and Flora" (On-line). Accessed Oct. 6, 2000 at

Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at

Fenton, M., G. Bell. 1979. Echolocation and feeding behaviour in four species of Myotis (Chiroptera). Canadian Journal of Zoology, 57: 1271-1277.

IUCN Species Survival Commission, 2000. "The 2000 IUCN Red List of Threatened Species Database Search" (On-line). Accessed Oct. 6, 2000 at

Nagorsen, D., M. Brigham. 1993. Royal British Columbia Museum Handbook: Bats of British Columbia. Vancouver, Canada: University of British Columbia Press.

National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at

Simpson, M. 1993. Myotis californicus. Mammalian Species, 428: 1-4.

U.S. Fish and Wildlife Service, 2000. "Endangered Species Program" (On-line). Accessed Oct. 6, 2000 at

Wilson, D., S. Ruff. 1999. Smithsonian Book of North American Mammals. Washington, U.S.A: Smithsonian Institution Press.