Myotis californicus
California myotis

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).

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).

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).

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).

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).

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

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).