Myotis lucifugus
little brown bat

Little brown bats, Myotis lucifugus, are abundant in southern Alaska, Canada, across the United States from the Pacific to Atlantic coasts, and the higher elevation forested regions of Mexico. Although little brown bats are not found in northern Canada, individuals have been observed in Iceland and Kamchatka. Those outlying records are presumed to have been the result of accidental ship transportation by humans. Little brown bats are also absent from much of Florida, the southern Great Plains regions of the U.S., southern California, and parts of coast Virginia and the Carolinas. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Nowak, 1994)

Myotis lucifugus occupies three types of roosts: day, night, and hibernation roosts. Locations of roosts are chosen based upon the presence of stable ambient temperatures. Day and night roosts are used by active bats and include, but are not limited to, buildings, trees, under rocks, and in piles of wood. Day roosts have very little or no light, provide good shelter, and typically have southwestern exposures to provide heat for arousal from daily torpor.

Night roosts are selected for their confined spaces where large concentrations of bats can cluster together to increase the temperature in the roost. These roosts are primarily occupied when temperatures are below 15°C. Night roosts are usually away from day roosts; this may diminish the accumulation of feces at day roosts and avoid signaling predators. Day and night roosts are inhabited during spring, summer, and fall months, whereas during the winter, hibernacula sites are used.

Nursery roosts are similar to day roosts but are warmer than ambient temperature. They are usually occupied only by females and their offspring. Females use the same nursery colony every year.

Hibernaculum sites may be shared with Myotis yumanensis. These sites usually include abandoned mines or caves where the temperature is continuously above freezing and humidity is high. Northern populations of bats enter hibernation in early September and end in mid-May; southern populations enter in November and end their hibernation in mid-March. Myotis lucifugus does not make tremendously long migrations during the change of seasons. (Fenton and Barclay, 1980; Koopman and Gudmundsson, 1966; Nowak, 1994; Wilson and Ruff, 1999)

Myotis lucifugus inhabits forested lands near water, but some subspecies can be found in dry climates where water is not readily available. In those habitats, drinking water is provided by moisture on cave walls or condensation on the fur. Little brown bats live over a wide latitudinal and elevational range. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Tuttle, 1991; Wilson and Ruff, 1999)

The fur of M. lucifugus is glossy, and varies in color from dark brown, golden brown, reddish, to olive brown. Albino individuals have also been observed. The ventral side has lighter pelage. The wing and interfemoral membranes are nearly hairless and dark brown or black. The tragus is blunt and of medium height. Their ears usually do not extend past the nose when laid forward. Myotis lucifugus has small ears and large hind feet. The fore and hind limbs have five metapodials. The hind foot has hairs that extend past the toes.

The skull has some distinguishing characteristics. Myotis lucifugus lacks a saggital crest, has a shortened rostrum, 38 teeth, and a upslope profile of the forehead. In addition, the braincase is flattened and subcircular when observed dorsally.

Myotis lucifugus does not possess a keel on the calcar and has a short tibia relative to the length of the hind foot (~55% of the tibial length). Myotis lucifugus lacks choroidal papillae and folded retinas, and therefore does not exhibit eye shine. (Fenton and Barclay, 1980; Kurta, 1995; Nowak, 1994)

Myotis lucifugus weighs between 5 and 14 g. The length varies between 60 and 102 mm, and the wingspan between 222 and 269 mm. The forearm, including claw, measures 33 to 41 mm, and tail length measures 28 to 65 mm. The hind foot is between 8 and 10 mm in length, ears are 11 to 15.5 mm, and the tragus is 7 to 9 mm. Little brown bats fly at speeds as high as 35 km/hour and average 20 km/hour. Females are larger than males, especially during the winter. (Fenton and Barclay, 1980; Nowak, 1994; Wilson and Ruff, 1999)

The lifespan of M. lucifugus is extended by their ability to find food and inhabit a variety of roosts. These characteristics allow expansion of their habitat to new ranges, but also contribute to their survival. Myotis lucifugus live approximately 6 to 7 years and often live well beyond 10 years. A 31 year-old male was discovered in southeastern Ontario. Evidence indicates that males tend to live longer than females. Mortality rate is the greatest during the first winter when new pups have considerably less weight than their adult counterparts at the start of hibernation. (Fenton and Barclay, 1980; Nowak, 1994)

Little brown bats are primarily nocturnal and emerge from their roosts at dusk. Primary activity occurs about two or three hours after dusk and secondary activity may occur before dawn; most individuals return to the roost by four or five o’clock in the morning. These bats usually enter daily torpor. During the winter, hibernation time depends on altitude and location of the roosts. It usually starts between September and November and ends in March to May. The young remain active longer in the fall to build fat deposits to last the winter. Myotis lucifugus does not migrate long distances for hibernation roosts. Individuals travel only up to 100 miles. This species does not show territoriality at roosts, and large colonies of as many as 300,000 bats have been reported in a single roost. (Barbour and Davis, 1969; Cockrum, 1956; Nowak, 1994)

During hibernation, little brown bats undergo repeated periods of torpor lasting 12 to 19 days, but may remain torpid for as long as 83 days. Signals for the end of hibernation include weather conditions of the area and arousal of neighboring bats. (Fenton and Barclay, 1980; Tuttle, 1991)

Little brown bats vary their body temperatures greatly. These bats can be cooled to 6.5 degrees Celsius and heated to temperatures of 54 degrees Celsius without harm. Myotis lucifugus deposits 13 distinct type of brown fat, allowing individuals to efficiently and rapidly produce heat during arousal from hibernation torpor.

Myotis lucifugus occultus can increase urine concentration in order to better withstand water stress in low humidity environments with limited water supply. Only this subspecies is known to do this, however; most subspecies of M. lucifugus have a poor ability to regulate urine concentration. In general, M. lucifugus usually lives within close proximity to water. (Fenton and Barclay, 1980; Tuttle, 1991)

Myotis lucifugus invests a large amount of time each day grooming. Individuals use their claws to groom the fur, and tongue and teeth to clean their wing membranes. (Fenton and Barclay, 1980)

Home Range

Little brown bats travel several kilometers between day roosts and feeding sites. (Nowak, 1994)

Myotis lucifugus produces frequency modulated (FM) calls at 45kHz, their fundamental frequency. These calls last 1 to 5 milliseconds and sweep from 80 to 40 kHz. Cruising bats typically produce 20 calls per second to detect prey and objects. (Fenton and Barclay, 1980; Fenton and Bell, 1979)

Myotis lucifugus alert other bats with non-echolocation calls if they are flying on a collision course during feeding. They emit this call by reducing the frequency of the terminal portion of a sweep call to 25 kHz. Additionally, they may use echolocation calls, visual cues, such as landmarks, and possibly chemical cues to locate roosts; they can find their roosts from 180 miles away. Mother and young communicate through a few, complex vocalizations. There is no information about alarm or distress calls. (Fenton and Barclay, 1980; Kurta, 1995)

Myotis lucifugus is an efficient insect predator, especially when insects are in patches and at close range (approximately less than one meter). Little brown bats, along with many other insectivorous bats, are opportunistic feeders and catch prey by aerial hawking and gleaning tactics. Myotis lucifugus flies faster near the end of the attack, when approaching prey. During gleaning, these bats hover approximately 30 cm from the prey. Myotis lucifugus typically feeds on swarms of insects, saving time and energy to search for food. There is no evidence of territorial protection of feeding areas, but individuals return to areas where they have had prior feeding success. Myotis lucifugus has different selectivity based upon the arrangements of insects. In large swarms of mating insects, these bats concentrate one or two species to feed on, but when insects are dispersed, little brown bats are less selective and feed on multiple species. Food demand of lactating females increases and pregnant or lactating females usually select larger insects than males or nonpregnant females. Normally, these bats feed on insects whose length ranges from 3 to 10 mm. These bats typically eat half of their body weight per night (when active) and lactating females eat approximately 110 percent of their body weight per night. Myotis lucifugus chews and processes food relatively quickly. Mastication rate is seven jaw cycles per second, and food takes only 35 to 54 minutes to pass items through the digestive system. (Anthony and Kunz, 1977; Belwood and Fenton, 1976; Fenton and Barclay, 1980; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999)

Myotis lucifugus uses FM echolocation, downward sweeping pulses of 80 to 40 kHZ that last from 1 to 5 msec. These wavelengths give the greatest quality of detection for 3 to 8 mm size prey, and M. lucifugus consumes prey averaging 3 to 10 mm in size. The same FM call is used for location of both flying and stationary insects. The approach phase of their call has second and third harmonics, but during the feeding buzz, the frequency is focused at 47kHz. The rate of call production while chasing prey is 200 calls per second. Myotis lucifugus emits a high-pulse repetitive call when nearing a landing site. (Anthony and Kunz, 1977; Barbour and Davis, 1969; Fenton and Barclay, 1980; Fenton and Bell, 1979; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999)

Myotis lucifugus catches free-flying insects in wooded areas, fields, and over water, but also preys on insects on the water surface. Insects caught during flight are taken by swooping or dipping maneuvers. Most activity over water occurs between 1 to 2 m over the surface and the insects are taken by the mouth. Most feeding activity occurs about two hours after dark. (Fenton and Bell, 1979)

Little brown bats feed largely on aquatic insects. Midges are the primary source of food of M. lucifugus, but a large part of their diet comes from other aquatic insects. When available, beetles are easily identified by echolocation and easily captured. Other insects consumed include caddisflies, moths, mayflies, lacewings, and occasionally mosquitoes. (Anthony and Kunz, 1977; Fenton and Barclay, 1980)

Domestic cats have become adept at catching bats due to the close proximities of roosts to human habitations. Many predators take advantage of the high concentrations of bats in roosts. Predators such as martens and fishers take advantage of weak young that fall or hibernating individuals that are dislodged by grooming activities. Other predators of M. lucifugus include mice, owls, weasels, hawks, snakes, raccoons, domestic cats, and other small carnivores. (Fenton and Barclay, 1980; Griffin, 1958)

Little brown bats have a major impact on the insect populations around their roosts. Active bats eat half of their body weight per night and lactating females eat more than their body weight per night. One M. lucifugus consumes approximately 3 to 7 grams of insects each night. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Wilson and Ruff, 1999)

Tapeworms, and ectoparasites such as fleas, mites and bed bugs are carried by little brown bats. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Fenton and Bell, 1979)

Myotis lucifugus is the target of control measures due to the abundance of the species. These bats inhabit attics, roofs, trees, and other areas in close proximity to humans; therefore, homeowners have spent large amounts of money trying to erradicate M. lucifugus from these areas. Rabies transmission to humans is extremely low, and only a small percentage of M. lucifugus are infected with the disease. Although rabies in M. lucifugus is low, other parasites such as tapeworms, fleas, mites and bed bugs are common. (Fenton and Barclay, 1980)

Members of this species are heavily researched and provide scientists with a bat model to test and study many aspects of the order, including echolocation, social behavior, feeding, and habitat use. Additionally, little brown bats eat pests that transmit diseases and eat agricultural products. They are also predators of mosquitoes and other pest around human habitats. (Barbour and Davis, 1969; Wilson and Ruff, 1999)

Myotis lucifugus is under no special conservation status as the species is abundant across North America. These bats thrives with expansion of human populations, as many of their roosting sites are built by humans. In spite of their overall abundance, some populations have suffered declines due to control measures and build-up of fat-soluble pesticides in their bodies. (Fenton and Barclay, 1980; Kunz, Anthony, and Rumage III, 1977)

There are six subspecies of M. lucifugus: M. l. alascensis, M. l. carissima, M. l. lucifugus, M. l. occultus, M. l. pernox, and M. l. relictus. Several of these subspecies were previously considered separate species: M. l. occultus, M. l. pernox, and M. l. carissima. (Fenton and Barclay, 1980; Hall, 1981)