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.
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.
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.
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.
Animal Foods: insects
Primary Diet: carnivore (Insectivore )
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.
Known Predators:
Anti-predator Adaptations: cryptic
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.
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.
Range mass: 5 to 14 g.
Range length: 60 to 102 mm.
Average length: 87 mm.
Range wingspan: 222 to 269 mm.
Other Physical Features: endothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger
Average basal metabolic rate: 0.051 W.
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.
Range lifespan
Status: wild: 31 (high) years.
Typical lifespan
Status: wild: 6 to 7 years.
Average lifespan
Status: wild: 6 to 7 years.
Average lifespan
Status: captivity: 30.0 years.
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.
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.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; mountains
Other Habitat Features: urban ; suburban ; agricultural ; riparian ; caves
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.
Biogeographic Regions: nearctic (Native )
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.
Tapeworms, and ectoparasites such as fleas, mites and bed bugs are carried by little brown bats.
Commensal/Parasitic Species:
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.
Positive Impacts: research and education; controls pest population
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.
Negative Impacts: injures humans (bites or stings, causes disease in humans , carries human disease); causes or carries domestic animal disease ; household pest
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.
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%.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
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.
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.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; acoustic ; ultrasound ; echolocation ; chemical
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.
Mating occurs between adult females and adult males; subadult males are not sexually mature until after their first year. Mating occurs in two phases: active and passive. During the active phase, both partners are awake and alert. In the passive phase, active males mate with torpid individuals of both sexes; passive phase mating is approximately 35% homosexual. Mating is random and promiscuous. Females in active phase usually mate with more than one male. In both active and passive phase matings, males mate with multiple females.
Mating System: polygynandrous (promiscuous)
Swarming at the hibernacula occurs during late summer and fall; activity decreases with lower temperatures. Swarming serves a prenuptial function, along with showing the young suitable hibernation roosts. During late July, bats arriving at the hibernacula are adult males and nonparous females; females and subadults appear in early August. Swarming M. lucifugus may travel large distances, causing mixing of populations from different areas. During the swarming period, little brown bats are receptive to calls of conspecifics.
Myotis lucifugus has enlarged pararhinal glands during the mating season. Mating occurs when a male mounts a female from the rear. The male may bite the female on her back. Upon female struggle, the male may emit a copulation call to ease the female. Males inseminate females that are are active as well as those that are torpid. Little brown bats delay ovulation and store sperm for about seven months between copulations in the fall and fertilization in the spring. Pups are born and reared in June and July after a 50 to 60 day gestation period. The greatest energy demand on females occurs during lactation and toward the end of pregnancy. Females lose the ability to thermoregulate well when approaching parturition.
Normally, bats hang head down; females giving birth reverse their position, so their head is up. Young are born into the interfemoral membrane; only one young is born per year. The pups’ eyes and ears open within hours of birth, and deciduous teeth are fully erupted. Pups must cling to the female’s nipple using their deciduous incisors, large thumbs, and hind feet. The young start hearing at day 2 and develop auditory sensitivity similar to that of an adult by day 13. On approximately day 9.5, pups are able to thermoregulate and in three weeks they are able to fly.
Independence from the mother comes when the pups start to fly and become self-supporting at about 4 weeks of age. Adult weight is attained at about 4 weeks of age as well. Spermatogenesis starts in May and ends in August.
Breeding interval: Both sexes mate more than once per year and produce one young per year.
Breeding season: Mating begins in mid-August during the active phase and continues in passive phase throughout the winter.
Range number of offspring: 1 to 2.
Average number of offspring: 1.
Range gestation period: 50 to 60 days.
Range weaning age: 21 to 28 days.
Average weaning age: 26 days.
Average time to independence: 4 weeks.
Average age at sexual or reproductive maturity (female): 210 days.
Average age at sexual or reproductive maturity (male): 210 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; sperm-storing ; delayed fertilization
Average birth mass: 1.96 g.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 210 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 210 days.
Mothers nurse their own young and distinguish from other pups by odor and calls. For 18 to 21 days, pups ingest only milk from their mother. Weaning takes place at about three weeks; at this time, the permanent teeth fully erupt and pups start to feed on insects along with the mother's milk. After weaning, the pups have a drop in body weight as they learn to catch insects. It is not clear if mothers bring insects to their young or help to teach them to hunt. However, many female/young pairs are captured together, suggesting that there is some period of supervised learning before independence. Males play no role in parental care.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
The little brown bat or little brown myotis[3] (Myotis lucifugus)[1] is an endangered species of mouse-eared microbat found in North America. It has a small body size and glossy brown fur. It is similar in appearance to several other mouse-eared bats, including the Indiana bat, northern long-eared bat, and Arizona myotis, to which it is closely related. Despite its name, the little brown bat is not closely related to the big brown bat, which belongs to a different genus.
Its mating system is polygynandrous, or promiscuous, and females give birth to one offspring annually. The offspring, called pups, are quickly weaned and reach adult size in some dimensions by three weeks old. The little brown bat has a mean lifespan of 6.5 years, though one individual in the wild reached 34 years old. It is nocturnal, foraging for its insect prey at night and roosting in hollow trees or buildings during the day, among less common roost types. It navigates and locates prey with echolocation.
It has few natural predators, but may be killed by raptors such as owls, as well as terrestrial predators such as raccoons. Other sources of mortality include diseases such as rabies and white-nose syndrome. White-nose syndrome has been a significant cause of mortality since 2006, killing over one million little brown bats by 2011. In the Northeastern United States, population loss has been extreme, with surveyed hibernacula (caves used for hibernation) averaging a population loss of 90%.
Humans frequently encounter the little brown bat due to its habit of roosting in buildings. Colonies in buildings are often considered pests because of the production of waste or the concern of rabies transmission. Little brown bats rarely test positive for rabies, however. Some people attempt to attract little brown bats to their property, but not their houses, by installing bat houses.
Old World spp.
Nearctic spp.M. lucifugus
Relationships of Nearctic Myotis species[4]The little brown bat was described as a new species in 1831 by American naturalist John Eatton Le Conte. It was initially in the genus Vespertilio, with a binomial of Vespertilio lucifugus,[5] before it was re-categorized as belonging to the Myotis genus.[6] "Myotis" is a Neo-Latin construction, from the Greek "muós (meaning "mouse") and "oûs" (meaning ear), literally translating to "mouse-eared".[7] "Lucifugus" is from Latin "lux" (meaning "light") and "fugere" (meaning "to shun"),[8] literally translating to "light-shunning".[9] The holotype had possibly been collected in Georgia near the Le Conte Plantation near Riceboro,[2] but this has been disputed because the initial record lacked detail on where the specimen was collected.[10]
Within its family, the Vespertilionidae (vesper bats), the little brown bat is a member of the subfamily Myotinae, which contains only the mouse-eared bats of genus Myotis.[6] Based on a 2007 study using mitochondrial and nuclear DNA, it is part of a Nearctic clade of mouse-eared bats. Its sister taxon is the Arizona myotis, M. occultus.[4]
As of 2005, five subspecies of the little brown bat are recognized: M. l. lucifugus, M. l. alascensis, M. l. carissima, M. l. pernox, and M. l. relictus.[11] Formerly, the Arizona myotis and southeastern myotis (M. austroriparius) were also considered subspecies (M. l. occultus and M. l. austroriparius),[2] but both are now recognized as full species.[12][11][13] In a 2018 study by Morales and Carstens, they concluded that the five subspecies are independent, paraphyletic lineages, meaning that grouping them together excludes other lineages with the same common ancestor, and therefore each warrant specific status.[14]
Results of one study suggested that the little brown bat can hybridize with Yuma myotis, M. yumanensis.[15] The two species occur in the same area in much of the Western United States, as well as southern British Columbia. The two species are morphologically different throughout most of the range, but in some regions, individuals have been documented that are intermediate in appearance between the two. However, a 1983 study by Herd and Fenton found no morphological, genetic, or ecological evidence to support the notion that the two species hybridize.[16]
The little brown bat is a small species, with individuals weighing 5.5–12.5 g (0.19–0.44 oz) with a total body length of 8.0–9.5 cm (3.1–3.7 in). Individuals have the lowest weight in the spring as they emerge from hibernation. It has a forearm length of 36–40 mm (1.4–1.6 in) and a wingspan of 22.2–26.9 cm (8.7–10.6 in).[17] It is a sexually dimorphic species, with females larger than males on average.[2] A variety of fur colors is possible, with pelage ranging from pale tan or reddish to dark brown. Its belly fur is a lighter color than its back fur.[17] Its fur is glossy in appearance, though less so on its belly.[2] A variety of pigmentation disorders have been documented in this species, including albinism (total lack of pigment), leucism (partial lack of pigment), and melanism (over-pigmentation).[18]
It is a diphyodont mammal, meaning that it has two sets of teeth during its lifetime—milk teeth and adult teeth. The dental formula of the milk teeth is 2.1.2.03.1.2.0 for a total of 22 teeth, while that of the adult teeth is 2.1.3.33.1.3.3 for a total of 38 teeth. Newborns ("pups") are born with 20 milk teeth which becomes 22 when the final upper premolars emerge. Pups begin losing milk teeth once they have reached a body length of 55–60 mm (2.2–2.4 in); total loss of milk teeth and emergence of adult teeth is usually complete by the time a juvenile is 80 mm (3.1 in) long.[19]
It has a relatively short snout and a gently sloped forehead. It lacks a sagittal crest, which can be used to distinguish it from the Arizona myotis.[2] Its skull length is 14–16 mm (0.55–0.63 in).[20] The braincase appears nearly circular though somewhat flattened when viewed from the back. Its ears are 11.0–15.5 mm (0.43–0.61 in) long, while the tragi, or cartilaginous flaps that project in front of the ear openings, are 7.0–9.0 mm (0.28–0.35 in) long. The tragi are blunt at the tips and considered of medium length for a mouse-eared bat.[2]
The little brown bat is dichromatic and its eyesight is likely sensitive to ultraviolet and red light, based on a genetic analysis that discovered that the genes SWS1 and M/LWS were present and functional. Its ability to see ultraviolet light may be useful in capturing insects, as 80% of nocturnal moths' wings reflect UV light. It is unclear if or how seeing red light is advantageous for this species.[21] It is adapted to see best in low-light conditions. It lacks eyeshine.[2]
The little brown bat lacks a vomeronasal organ.[2] Relative to frugivorous bat species such as the Jamaican fruit bat, it has small eyes and a reduced olfactory epithelium.[22] Instead, it has a more sophisticated system of echolocation, suggesting that reliance on echolocation decreases the need for orientation via sight or smell.[22]
In fall through spring, the little brown bat enters torpor, a state of decreased physiological activity, daily. Torpor saves energy for the bat when ambient temperatures are below 39 °F (4 °C) throughout the year and 32 °F (0 °C) in the winter; instead of expending energy to maintain a constant body temperature, it allows its body to cool and physiological activity to slow. While in torpor, its heart rate drops from up to 210 beats per minute to as few as 8 beats per minute. The exception to this rule is females at the end of pregnancy, which no longer have the ability to thermoregulate, and therefore must roost in warm places. During daily roosting, it can cope with high levels of water loss of up to 25%.[2]
In the winter time, it enters a prolonged state of torpor known as hibernation. To conserve energy, it limits how frequently it arouses from torpor, with individuals existing in uninterrupted torpor for up to 90 days. Arousal is the most energetically costly phase of torpor, which is why individuals do so infrequently. Despite the energy-saving mechanism of hibernation, individuals lose a quarter of their pre-hibernation body mass during the winter.[2]
The little brown bat can be confused with the Indiana bat (M. sodalis) in appearance. The two can be differentiated by the little brown bat's lack of a keeled calcar—the cartilaginous spur on its uropatagium (the flight membrane between its hind legs). While it does have a calcar, that of the little brown bat is not nearly as pronounced. Additionally, the little brown bat can be distinguished by the presence of hairs on its toes and feet that extend beyond the length of the digits.[2] The northern long-eared bat (M. septentrionalis), another similar species, can be distinguished by its much longer ears, and tragi that are long and sharply pointed.[17]
The little brown bat has a promiscuous mating structure, meaning that individual bats of both sexes mate with multiple partners.[23] It is a seasonal breeder, with mating taking place in the fall before the annual hibernation.[17] As a seasonal breeder, males do not produce sperm year-round; instead, spermatogenesis occurs May through August each year.[2] Throughout the spring and summer, males and females roost separately. In the fall, however, individuals of both sexes will congregate in the same roost in a behavior known as "swarming".[24] Like several other bat species, males of this species exhibit homosexual behaviors, with male bats mating indiscriminately with torpid, roosting bats, regardless of sex.[25]
Although copulation occurs in the fall, fertilization does not occur until the spring due to sperm storage.[17] Gestation proceeds for 50–60 days following fertilization. The litter size is one individual.[2] At birth, pups weigh approximately 2.2 g (0.078 oz) and have a forearm length less than 17.2 mm (0.68 in).[26] While they have a small absolute mass, they are enormous relative to their mothers, weighing up to 30% of her postpartum body weight at birth.[27] Pups' eyes and ears are closed at first, but open within a few hours of birth. They exhibit rapid growth; at around three weeks old, the young start flying, begin the weaning process, and are of a similar size to adults in forearm length but not weight. The young are totally weaned by 26 days old.[27] Females may become sexually mature in the first year of life.[2] Males become sexually mature in their second year.[7]
It is a very long-lived species relative to its body size. In the wild, individuals have been documented living up to 34 years.[28] The average lifespan, however, is around 6.5 years. Males and females have high annual survival rates (probability of surviving another year), though survival rates vary by sex and region. One colony documented in Ontario had a male survival rate of 81.6% and a female survival rate of 70.8%; a colony in southern Indiana had survival rates of 77.1% and 85.7% for males and females, respectively.[29]
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The little brown bat is a colonial species, with hibernating colonies consisting of up to 183,500 individuals, though the average colony size is little more than 9,000. Historically, individuals within these colonies were highly aggregated and densely clustered together, though the disease white-nose syndrome is making solitary hibernation more common.[30]
During the spring and summer, maternity colonies of almost all female individuals form.[2] These colonies usually consist of several hundred bats.[31] Outside of these maternity colonies, adult males and non-reproductive females will roost by themselves or in small aggregations. Maternity colonies begin to break apart in late summer.[2]
The little brown bat is nocturnal, resting during the day and foraging at night. Individuals typically emerge from their roosts at dusk, foraging for 1.5–3 hours before stopping to roost. A second foraging bout usually occurs later in the night, ending at dawn.[32]
Based on documenting one individual flying in a wind tunnel, it flies at approximately 5.5 km/h (3.4 mph); this increased to 8.9 km/h (5.5 mph) when flying over the surface of water.[33] Home range size is variable; in one study of 22 females in Canada, pregnant females had an average home range of 30.1 hectares (74 acres) and lactating females had an average of 17.6 hectares (43 acres).[34]
It produces calls that are high intensity frequency modulated (FM) and that last from less than one millisecond (ms) to about 5 ms and have a sweep rate of 80–40 kHz, with most of their energy at 45 kHz.[35] Individuals emit approximately 20 calls per second when in flight.[2][35]
It consumes a variety of arthropod species, including insects and spiders. Prey species include beetles, flies, mayflies, true bugs, ants, moths, lacewings, stoneflies, and caddisflies.[36] It also consumes mosquitoes, with one study documenting that, across twelve colonies in Wisconsin, 71.9% of all little brown bat guano (feces) samples contained mosquito DNA.[37]
During late pregnancy, when energetic demands are high, females consume around 5.5 g (0.19 oz) of insects nightly, or 1.3 g (0.046 oz) of insects per hour of foraging. With an average body mass of 9.0 g (0.32 oz), that means that pregnant females consume 61% of their body weight nightly. Energetic demands during lactation are even higher, though, with females consuming 6.7 g (0.24 oz) of insects nightly, or 1.7 g (0.060 oz) of insects per hour of foraging. Because lactating females have an average mass of 7.9 g (0.28 oz), this means that they consume nearly 85% of their body weight nightly. As the pup grows, lactation requires more and more energy; at the predicted lactation peak of 18 days old, a female would have to consume 9.9 g (0.35 oz) of insects per night, or 125% of her own weight.[27]
An often-mentioned statement is that "bats can eat 1000 mosquitoes per hour."[37][38][39] While the little brown bat does consume mosquitoes and has high energetic needs, the study that is the basis for this claim was an experiment in which individuals were put into rooms full of either mosquitoes or fruit flies.[37][38] For a duration up to 31 minutes, they captured an average of 1.5–5.7 mosquitoes per minute. The individual most efficient at catching fruit flies caught an average of 14.8 per minute for 15 minutes.[40] Extrapolating these numbers results in conclusions that it can eat approximately 340 mosquitoes per hour, or 890 fruit flies. However, there is no assurance that individuals forage with such high efficiencies for long periods of time, or that prey is dense enough in natural settings to allow capture rates observed in enclosed areas.[38]
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The little brown bat likely has few predators. Known predators include owls such as the eastern screech owl, northern saw-whet owl, and the great horned owl.[41] Raccoons are also opportunistic predators of the little brown bat, picking individuals off the cave walls of their hibernacula (caves used for hibernation) or eating individuals that have fallen to the cave floor.[42]
The presence of helminth parasites in the gastrointestinal tract of the little brown bat is most common in the spring and fall and least common in the summer. Digenetic trematodes are the most common of these parasites, with the more common of these species including Ototrema schildti and Plagiorchis vespertilionis.[43] The little brown bat is also affected by ectoparasites (external parasites), including bat fleas such as Myodopsylla insignis, chiggers like Leptotrombidium myotis, and the bat mites Spinturnix americanus.[44] When parasitizing a female bat, bat mites synchronize their reproductive cycle with that of their host, with their own reproduction tied to the host's pregnancy hormones. Lactating females have a higher intensity of parasitization by mites, which may promote vertical transmission—the transfer of mites to the bat's offspring.[45]
The little brown bat is affected by the rabies virus—specifically, the strain associated with this species is known as MlV1. However, it is susceptible to other strains of the virus, including those of the big brown bat and the silver-haired bat, which is most lethal to humans. The rabies virus can be present in an individual's saliva, meaning that it can be spread through bites, 12–18 days before the individual begins showing symptoms. Individuals do not always develop rabies after exposure, though. In one study, no little brown bats developed rabies after subcutaneous exposure to the MlV1 strain.[46] Some individuals in the wild have antibodies for the rabies virus.[47]
The little brown bat is also susceptible to the disease white-nose syndrome, which is caused by the fungus Pseudogymnoascus destructans.[48] The disease affects individuals when they are hibernating, which is when their body temperatures are within the ideal growth range of P. destructans, 1–15 °C (34–59 °F).[49] Pseudogymnoascus destructans is the first known pathogen that kills a mammal host during its torpor.[50] Mortality from white-nose syndrome begins to manifest 120 days after hibernation begins, and mortality peaks 180 days after bats enter hibernacula.[51] The growth of P. destructans on bats erodes the skin of their wing and tail membranes, muzzles, and ears. White-nose syndrome causes affected bats to burn through their energy reserves twice as fast as uninfected individuals. In addition to visible fungus growth on the nose, ears, and wings, white-nose syndrome results in higher carbon dioxide levels in the blood, causing acidosis, and hyperkalemia (elevated blood potassium). Arousal from torpor becomes more frequent, and water loss increases due increased respiration rate in an attempt to remove excess carbon dioxide from the blood.[52] The premature loss of fat reserves during hibernation results in starvation.[50]
Survivors of white-nose syndrome have longer bouts of torpor and lower bodies temperatures during torpor than individuals that die.[50] Some individuals are more likely to survive based on their genetics, which predisposes them to remain in torpor longer and have larger fat reserves.[53] Little brown bats are most affected by white-nose syndrome when they exhibit social, grouping behavior when hibernating, as P. destructans is transmitted by direct contact. In hibernacula where bats exhibit more solitary behavior, colonies are more prone to avoid infections of white-nose syndrome. In some colonies where grouping behavior was common before exposure to white-nose syndrome, bats now hibernate in a more solitary fashion. Before white-nose syndrome, only 1.16% of little brown bats hibernated singly; after white-nose syndrome, the percentage grew to 44.5%.[30]
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The little brown bat lives throughout much of North America.[2] In the north, its range extends as far west as Alaska and across much of Canada to Labrador. In the south, its range extends to Southern California and across the northern parts of Arizona and New Mexico.[1] Historically, the largest known aggregations of this species occurred in the karstic regions of the Eastern United States.[48]
The little brown bat roosts in sheltered places during the day. These roosts can include human structures or natural structures such as tree hollows, wood piles, rocky outcrops, or, occasionally, caves.[54][2] Species of trees used for roosting include quaking aspen, balsam poplar, oak, and maple.[55][56][17] It prefers roosts that are warm and dark.[2] For maternity colonies, females prefer roosts that are 23.3–34.4 °C (73.9–93.9 °F).[17]
The little brown bat hibernates in caves or old mines. Females migrate up to hundreds of kilometers from their summer ranges to reach these hibernacula. It prefers hibernacula in which the relative humidity is greater than 90% and ambient temperatures are above the freezing point.[2] Preferred hibernacula also maintain a constant temperature throughout the winter.[17]
The little brown bat forages along the edges of vegetated habitat.[55] It also forages along the edges of bodies of water or streams.[2] In one study in the Canadian province of Alberta, its foraging activity was significantly higher in old-growth forest than would be expected based on its relative availability.[55]
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As of 2018, the little brown bat is evaluated as an endangered species by the IUCN, a dramatic change from 2008 when it was designated as the lowest conservation priority, least concern.[1] Until recently, the species was regarded as one of the most common bats in North America.[57] However, a serious threat to the species has emerged in the form of a fungus-caused disease known as white-nose syndrome.[58] It was one of the first bat species documented with the disease, which now affects at least seven hibernating bat species in the United States and Canada.[48] From 2006 to 2011, over one million little brown bats died from the disease in the Northeastern United States, with winter hibernacula populations declining up to 99%.[58] As of 2017, hibernacula counts for little brown bats in the Northeast had declined by an average of 90%.[59]
White-nose syndrome first appeared in New York in 2006; it has steadily diffused from eastern New York, though, until recently, remaining east of the Rocky Mountains. In March 2016, white-nose syndrome was detected on a little brown bat in King County, Washington, representing a 1,300 mi (2,100 km) jump from the previous westernmost extent of the disease in any bat species.[60]
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In 2010, Frick et al. predicted a 99% chance of local extinction of little brown bats by the year 2026. They also predicted that the pre-white-nose syndrome population of 6.5 million individuals could be reduced to as few as 65,000 (1%) via the disease outbreak.[61] Despite heavy declines, the species has avoided extinction in the Northeast through the persistence of small, localized populations. While the mortality rate of the disease is very high, some individuals that are exposed do survive.[59]
In 2010, Kunz and Reichard published a report arguing that the precipitous decline of the little brown bat justified its emergency listing as a federally endangered species under the U.S. Endangered Species Act.[62] However, it is not federally listed as threatened or endangered as of 2018, though several U.S. states list it as endangered (Connecticut,[63] Maine,[64] Massachusetts,[65] New Hampshire,[66] Pennsylvania,[67] Vermont,[68] Virginia[69]), threatened (Tennessee,[70] Wisconsin[17]), or of Special Concern (Michigan,[71] Ohio[72]).
The little brown bat was listed as an endangered species by the Committee on the Status of Endangered Wildlife in Canada in February 2012 after an emergency assessment. The emergency designation as endangered was confirmed in November 2013.[73]
Little brown bats commonly occupy human structures. Females will situate maternity colonies within buildings.[74] This small body size of this species can make it challenging to prevent individuals from entering a structure, as they can take advantage of gaps or holes as small as 3.8 cm (1.5 in) × 0.64 cm (0.25 in). Once inside a building, a colony of little brown bats can disturb human inhabitants with their vocalizations and production of guano and urine. Large accumulations of guano can provide a growth medium for fungi, including the species that causes histoplasmosis. Concerns about humans becoming affected by bat ectoparasites such as ticks, fleas, or bat bugs are generally unfounded, as parasites that feed on bats are often specific to bats and die without them.[75]
Because they are often found in proximity to humans, the little brown bat and the not-closely related big brown bat are the two bat species most frequently submitted for rabies testing in the United States.[46] Little brown bats infrequently test positive for the rabies virus; of the 586 individuals submitted for testing across the United States in 2015, the most recent data available as of 2018, 16 (2.7%) tested positive for the virus.[76]
Little brown bats are a species that will use bat houses for their roosts.[77] Landowners will purchase or construct bat houses and install them, hoping to attract bats for various reasons. Some install bat houses in an attempt to negate the effects of removing a colony from a human structure ("rehoming" them into a more acceptable space). While this can be effective for other species, there is not evidence to suggest that this is effective for little brown bats,[74] though it has been shown that little brown bats will choose to occupy artificial bat boxes installed at the sites of destroyed buildings that once housed colonies.[78] Others are attempting to help bats out of concern for them due to the effects of white-nose syndrome.[79] Bat houses are also installed in an attempt to control the bats' insect prey such as mosquitoes or taxa that harm crops.[80]
Little brown bats are vulnerable near moving vehicles on roads, either foraging or crossing. Bats can easily be pulled into the slipstreams of faster moving vehicles. When little brown bats cross roads, they approach the road using canopy tree cover and avoid crossing where there is no cover. When the cover is lower, bats cross roads lower.[81]
Since 2020, the little brown bat has been the official state mammal of Washington, D.C.
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{{cite journal}}: Cite journal requires |journal= (help) The little brown bat or little brown myotis (Myotis lucifugus) is an endangered species of mouse-eared microbat found in North America. It has a small body size and glossy brown fur. It is similar in appearance to several other mouse-eared bats, including the Indiana bat, northern long-eared bat, and Arizona myotis, to which it is closely related. Despite its name, the little brown bat is not closely related to the big brown bat, which belongs to a different genus.
Its mating system is polygynandrous, or promiscuous, and females give birth to one offspring annually. The offspring, called pups, are quickly weaned and reach adult size in some dimensions by three weeks old. The little brown bat has a mean lifespan of 6.5 years, though one individual in the wild reached 34 years old. It is nocturnal, foraging for its insect prey at night and roosting in hollow trees or buildings during the day, among less common roost types. It navigates and locates prey with echolocation.
It has few natural predators, but may be killed by raptors such as owls, as well as terrestrial predators such as raccoons. Other sources of mortality include diseases such as rabies and white-nose syndrome. White-nose syndrome has been a significant cause of mortality since 2006, killing over one million little brown bats by 2011. In the Northeastern United States, population loss has been extreme, with surveyed hibernacula (caves used for hibernation) averaging a population loss of 90%.
Humans frequently encounter the little brown bat due to its habit of roosting in buildings. Colonies in buildings are often considered pests because of the production of waste or the concern of rabies transmission. Little brown bats rarely test positive for rabies, however. Some people attempt to attract little brown bats to their property, but not their houses, by installing bat houses.
