Little brown bats are appropriately named. Their fur is glossy, and can be dark-brown, golden-brown, reddish, or olive-brown. Albino individuals have also been observed. The fur on the belly is lighter than the fur on the back. Wings and membranes between the legs are dark brown or black, and have almost no hair. Little brown bats have small ears and large hind feet. The hind foot has hairs that extend past the toes. (Wilson and Ruff, 1999; Fenton and Barclay, 1980; Kurta, 1995; Nowak, 1994; Wilson and Ruff, 1999)
Little brown bats are tiny, and weigh between 5 and 14 g. They are between 60 and 102 mm long, and have a wingspan between 222 and 269 mm. Females are larger than males, especially during the winter. Little brown bats fly at speeds as high as 35 km/hour and average 20 km/hour. (Fenton and Barclay, 1980; Nowak, 1994; Wilson and Ruff, 1999)
Little brown bats are found in most parts of North America. They are not found in the far north of Canada or in the far southern parts of the United States, except in the forested high mountains of Mexico. Some little brown bats have been observed in Iceland and Kamchatka, but those probably got there as the result of accidental ship transportation by people. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Nowak, 1994)
One of the most important aspects of little brown bat habitat is the presence of good roosts. Little brown bats use three different kinds of roosts: day, night, and hibernation roosts. In order for a place to serve as a roost, the air temperature there must remain about the same all the time. Day and night roosts are used by active bats. These roosts can be found in buildings, in trees, under rocks, and in piles of wood. Day roosts have very little or no light, and provide good shelter. Day roosts often have southwestern exposures, which provide heat to wake the bats up from their daily sleep.
Night roosts have closed-in spaces where lots of bats can cluster together. This helps to make the roost warmer. Little brown bats use night roosts when temperatures are below 15°C. These roosts are usually not in the same place as day roosts. Separation of day and night roosts may keep feces from piling up, which may help to keep the roost's location a secret from predators. Day and night roosts are used during spring, summer, and fall. During the winter, little brown bats use hibernaculum sites.
Nursery roosts are like day roosts, but they are warmer than the surrounding air. They are usually occupied only by females and their babies. Females use the same nursery colony every year.
Roosts used during the winter are called hibernaculum sites. These may be shared with Myotis yumanensis. Winter roosts include abandoned mines or caves where the temperature is continuously above freezing and humidity is high. In the north, little brown bats enter hibernation in early September and end in mid-May. In the south, hibernation begins in November and ends in mid-March. Unlike some bats, little brown bats do not make long migrations during the change of seasons. (Fenton and Barclay, 1980; Koopman and Gudmundsson, 1966; Nowak, 1994; Wilson and Ruff, 1999)
Little brown bats are most often found in forested areas near water. Some subspecies live in dry climates where there is not much water to drink. In these habitats, drinking water comes from moisture on cave walls or dew that settles on the fur. (Barbour and Davis, 1969; Fenton and Barclay, 1980; Tuttle, 1991; Wilson and Ruff, 1999)
Little brown bats mate in two different ways. Mating occurs right before hibernation in the hibernaculum roost. Sometimes both the male and female are awake and alert when mating takes place. But sometimes, males mate with other bats who have already entered hibernation. Mating is random and both males and female mate with more than one other bat. (Fenton and Barclay, 1980; Wai-Ping and Fenton, 1988)
Little brown bats hibernate in a special roost called a hibernaculum. When the temperature falls during late summer and autumn, bats begin swarming at the hibernaculum. Swarming helps young bats find suitable hibernation roosts. The first bats to arrive at the hibernaculum in late July are adult males, and females without young. Females and subadults arrive in August. (Fenton and Barclay, 1980; Schowalter, 1980)
Even though little brown bats mate in autumn, females delay ovulation and store sperm for about seven months before they actually get pregnant in spring. Pregnancy lasts 50 to 60 days. Pups are born in June and July. Females give birth to only one pup each year. (Fenton and Barclay, 1980; Wai-Ping and Fenton, 1988)
Normally, bats hang with their heads pointed down. When females give birth, they reverse their position so the head is up. Mothers catch their newborn young in a special membrane between their legs. A pup is born with a full set of teeth. Its eyes and ears open within hours of birth. A pup clings to to its mother's nipple using its teeth, thumbs, and hind feet.
When the bat pups are 9.5 days old, they can control the temperature of their bodies. They can hear as well as adults by the time they are 13 days old. Young can fly by the time they are 3 weeks old. Pups become independent and self-supporting about 4 weeks after they are born. By this time they are as big as adults. (Fenton and Barclay, 1980)
Mother little brown bats provide all of the parental care. A mother can identify her own pup by its odor and its calls.
The mother provides milk to her young, and for 18 to 21 days this is all the pup eats. At about 3 weeks of age, the permanent teeth of a pup come in, allowing it to feed on insects along with the mother's milk.
Weaned pups lose weight when they are first learning to catch insects. Scientists are not sure if mothers bring insects to their young or actively teach them to hunt. However, because mothers and their young stay together, scientists believe that the young are learning from their mother before they become independent. (Fenton and Barclay, 1980)
Little brown bats can find food almost anywhere and can use a variety of roosts. This allows them to survive in changing conditions.
A normal life span for these animals is 6 to 7 years, though some live well beyond 10 years. Males usually live longer than females. One 31 year-old male was discovered in southeastern Ontario, although these bats usually don't live so long. A little brown bat is most likely to die during its first winter, since new pups have considerably less weight than adults do at the start of hibernation. (Fenton and Barclay, 1980; Nowak, 1994)
Little brown bats are active at night and emerge from their roosts when the sun is going down. They are most active two or three hours after dusk and again just before dawn. Most bats return to their roosts by four or five o'clock in the morning.
Little brown bats hibernate during the winter. Hibernation usually starts between September and November and ends in March to May. Young bats who have not reached their first birthday remain active longer in the fall than adult bats do. This gives them time to feed and to build up enough fat deposits to survive during the winter. Little brown bats may travel up to 100 miles to find a suitable hibernation roost.
During hibernation, little brown bats usually enter a deep sleep for 12 to 19 days at a time, but can sleep for as long as 83 days. Signals for the end of hibernation include warmer weather and arousal of other bats in the colony. (Fenton and Barclay, 1980; Tuttle, 1991)
The body temperature of little brown bats varies greatly. These bats can be cooled to 6.5 degrees Celsius and heated to temperatures of 54 degrees Celsius without harm. When they are in their deep hibernation sleep, their body temperature is lowest. Little brown bats have 13 distinct type of brown fat in their bodies, which allows individuals to warm their bodies quickly when waking up from hibernation.
Some subspecies are able to subsist on lower water supplies than others. This allows them to live further from water and in drier environments than subspecies that need more water. (Fenton and Barclay, 1980; Tuttle, 1991)
Little brown bats spend a lot of time grooming. These bats use their claws to groom their fur, and their tongues and teeth to clean their wing membranes. (Fenton and Barclay, 1980)
Little brown bats travel several kilometers between day roosts and feeding sites. (Nowak, 1994)
Little brown bats use echolocation to find prey. In echolocation, the bat blasts out calls and listens for the echo. From the echo, the bat can determine where an object is located. Echolocation allows them to find bugs to eat, and to avoid hitting objects while flying. (Fenton and Barclay, 1980; Fenton and Bell, 1979)
Little brown bats make other calls to communicate with each other. An example of such a call is when two bats are flying on a collision course during feeding.
These animals may use echolocation calls, visual cues (such as landmarks), and possibly scent cues to locate roosts. A roost can be located from 180 miles away.
Mother and young communicate through vocalizations. There is also some information transmitted in physical contact between the mother and her young.
Little brown bats eat insects. They are very good at catching insects, especially when they are in patches and are less than one meter away. These bats will catch whatever insects are available. Their food may be captured straight out of the air, or may be picked off of surfaces.
Little brown bats fly faster near the end of an attack when the prey is very close. They usually feed on swarms of insects. Large swarms of insect make it easier for the bats to capture them.
These bats do not protect feeding terrietories, but individuals do return to areas where they have had prior feeding success.
Females who are nursing young need more food than other bats. These females usually select larger insects than male bats or female bats without young. Little brown bats usually eat insects that are from 3 to 10 mm long. An active bat can eat half of its own body weight in insects each night. Females with nursing young eat 110 percent of their body weight per night.
These animals eat their food quickly. The food takes only 35 to 54 minutes to pass through the digestive system. (Anthony and Kunz, 1977; Belwood and Fenton, 1976; Fenton and Barclay, 1980; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999; Anthony and Kunz, 1977; Belwood and Fenton, 1976; Fenton and Barclay, 1980; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999)
The echolocation calls used by little brown bats work the best for finding prey insects between 3 and 8 mm long. This is close to the size of insects most often eaten by these bats, which is between 3 and 10 mm. The same call is used to locate both flying and sitting insects. (Anthony and Kunz, 1977; Barbour and Davis, 1969; Fenton and Barclay, 1980; Fenton and Bell, 1979; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999; Anthony and Kunz, 1977; Barbour and Davis, 1969; Fenton and Barclay, 1980; Fenton and Bell, 1979; Ratcliffe and Dawson, 2003; Wilson and Ruff, 1999)
Little brown bats catch insects in wooded areas, fields, and over water. These insects are captured as the bats swoop and dip through the air. Insects on the water surface may also be caught. Bats do most of their feeding about two hours after dark. (Fenton and Bell, 1979; Fenton and Bell, 1979)
Little brown bats eat a lot of insects that live in the water. Midges provide these bats with most of their food, but other aquatic insects are eaten, too. Beetles, caddisflies, moths, mayflies, lacewings, and mosquitoes are all eaten sometimes. (Anthony and Kunz, 1977; Fenton and Barclay, 1980)
House cats are good at catching bats, and have many chances since bats often roost near human habitations. 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 little brown bats 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)
Little brown bats are abundant, and because they have some possible negative effects on humans, people have spent a lot of money trying to eliminate them from some areas. These bats live in attics, roofs, trees, and other areas that put them into contact with humans. These bats sometimes carry rabies, although transmission to humans rarely occurs. Still, other parasites such as tapeworms, fleas, mites and bed bugs are common in these bats, and make them unwanted additions to the community in many areas. (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, et al., 1977)
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%. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)
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