California myotis (bat) (Myotis californicus)

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Category: Mammals

Description and Range

Physical description

California myotis are one of the smallest bats in Washington . Fur coloration of the two subspecies found in Washington ranges from rusty to blackish brown and lacks a glossy sheen, with M. c. caurinus having darker fur than M. c. californicus. Ears and flight membranes are black. The ears are relatively short, but nevertheless extend beyond the nose when pressed forward. The tragus is long and narrow. The hind foot is relatively small and less than half the tibia length, and the calcar has a distinct keel.

Food Habits and Foraging
In most studies from the Pacific Northwest, moths and flies dominate the diet, with beetles, caddisflies, neuropterans, termites, and bees/ants also sometimes eaten in significant amounts. Spiders are also sometimes consumed. Foraging is often greatest within a few hours of darkness, with additional peaks in activity sometimes noted during the rest of the night. Foraging occurs over water, near the ground, within the forest canopy, along forest margins, and high above open ground. California myotis have rounded wing tips, low wing loading, and low aspect ratios, which give them slow maneuverable flight. Their high frequency echolocation suggests that most insects are detected at close range. Foraging is known to extend through winter in parts of western Washington.

Mating occurs in the late fall in most of the range, including the Pacific Northwest. Sperm are stored overwinter and fertilization occurs in spring. One young is born annually and births occur from about May to early July in Oregon, Washington, British Columbia, and Alaska. Young are able to fly at about one month of age.

Geographic range

California myotis range southward from southeastern Alaska and southern British Columbia to much of the western U.S., Mexico, and Guatemala. This species is present in all counties in Washington. Some records from eastern Washington may be erroneous because of past confusion with western small-footed myotis.

California myotis inhabit deserts, canyons, shrub-steppe, arid grasslands, and dry interior forests, as well as moister environments such as humid coastal and montane forests comprised of deciduous or coniferous trees, riparian forests, and mountain. Urban and semi-urban locations are also used. In arid regions, presence is commonly dependent on the availability of water sources. Elevations from sea level to 2,750 m are occupied.

Roost sites include crevices beneath tree bark and rocks; in tree cavities, caves, mines, buildings, and bridges; on shrubs; and on the ground. Maternity colonies occur in many of these same types of sites. Females most frequently roost under loose bark in trees or snags in intermediate stages of decay.  Roost trees probably remain suitable for periods of only a few years. Males occasionally use stumps as day roosts. This species appears flexible in its choice of night roosts and may use any natural or human-made shelter. Mines, caves, buildings, tree hollows, rock crevices, bridges, trees, and shrubs are among the structures occupied at night. California myotis hibernate alone or in small groups in buildings, caves, and mines.

In Washington, Oregon, and British Columbia, this species commonly hibernates in buildings and has been found in lava tubes. Winter surveys of more than 650 caves and 70 buildings in these states during the 1980s found single individuals at just two caves in Oregon. Both sexes roost together in fall and winter. In western and eastern Washington and elsewhere, this species emerges from hibernation to become active on both mild and below freezing evenings.


  • Retention and recruitment of large trees and snags during timber harvest is likely crucial to the conservation of California myotis in forested landscapes.
  • On intensively man-aged forests, management agreements and incentives for protecting large-diameter roost trees and snags are desirable.
  • Maintaining remnant patches of structurally diverse forest with abundant large snags is another protective strategy.
  • Where eviction from buildings is necessary, non-lethal exclusion measures should be taken to minimize negative impacts on the bats.
  • Precautions to reduce disturbance should be taken when mine and cave surveys are conducted during the breeding season and winter hibernation.
  • Seasonal inventories of bat use should be conducted at mines and caves considered for closure, with bat gates installed where occupancy is documented.
  • Before pesticide spraying projects, surveys to identify roosting and foraging habitat should be conducted to avoid spraying of important habitats.

Preventing conflict

For some people bats don't present a problem. For others, bats can be a worry, especially when they become unwanted guests in an attic, inside a wall of a home, or inside the home itself.

Unlike rodents, bats only have small teeth for eating insects, so they do not gnaw holes in walls, shred material for nests, chew electrical wiring, or cause structural damage to buildings. Damage caused by bats is usually minimal, but they can be noisy and alarming, and the smell of bats and their droppings can be offensive. It is possible to learn to coexist with bats, and to benefit from their presence.‚Äč Learn more on our Living with Wildlife: Bats webpage.