Little Brown Bat

 Photo Merlin D. Tuttle, Bat Conservation International

Little Brown Bat

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The Alaska Zoo is a partner in the Alaska Citizen Science Program, which monitors the sightings, distribution and ecology of bats and other non-game species in our state.  Learn about this program and how to REPORT YOUR BAT SIGHTINGS to help scientists learn about them.


The fur of the little brown bat is cinnamon-buff to dark brown above, buffy to pale gray below. The hairs on their back have long glossy tips. When laid forward, their ears reach approximately to the nostril. The wing and interfemoral membranes are nearly hairless and dark brown or black. The fore and hind limbs have five digits. They have 38 teeth. Females are larger than males, especially during the winter.  They are difficult to identify from other bat species by an inexperienced observer.   


Little brown bats fly at speeds as high as 22 miles per hour and average 12 miles per hour.  The little brown bat occupies three types of roosts (resting places): Day, night, and hibernation roosts.  Locations of roosts are chosen based on 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.  Night roosts are usually away from day roosts, which 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.  The little brown bat hibernates from Sept/Oct to Apr/May.  Hibernacula include, but are not limited to, caves, tunnels, abandoned mines and similar sites.  Signals for the end of hibernation include weather conditions of the area and arousal of neighboring bats.  Little brown bats are primarily nocturnal and emerge from their roosts at dusk.  Most activity occurs about two or three hours after dusk and secondary activity may occur before dawn.  The lifespan of the little brown bat is extended by their ability to find food and inhabit a variety of roosts.  They typically live to 10 years, but may live as long as 20-30 years.  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.  The invest a large amount of time each day grooming. Individuals use claws to groom fur, and tongue and teeth to clean wing membranes.

Food Habits

Little brown bats often hunt over water or along lakes and streams, as well as away from water.  Their diet consists of flying insects, especially mosquitoes, midges, caddisflies, moths, various hoppers, smaller beetles and sometimes spiders. Prey with wingspans of 1/8-1/2 inches are pursued and detected by echolocation at a range of 3.3 feet (1 meter).  Most feeding activity occurs about two hours after dark.  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.  They chew and process food quickly, taking less than an hour to pass items through the digestive system.  These nocturnal mammals use echolocation to navigate and locate prey. They send out signals and listen for those signals to return, with sensitive hearing and huge ears to help them pinpoint the prey.  They swoop and catch the insects in their mouths, but can use their wing and tail membranes to help as needed.


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.  Mating usually occurs in September-October.  However, ovulation and fertilization are delayed until spring.  Gestation lasts about 50-60 days.  The female gives birth to one offspring (pup) in late spring to early summer.  The eyes and ears open within hours of birth.  Pups must cling to the female’s nipple using their incisors, large thumbs, and hind feet.  Mothers nurse their own young and distinguish from other pups by odor and calls.  For 18 to 21 days, pups eat only milk from their mother.  Weaning happens at about three weeks.  The pups start hearing at day two 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.  Adult weight is attained at about 4 weeks of age as well. Females usually produce their first young in the first or second year of their lives. Males play no role in parental care.

Population Status, Threats & Conservation

Little brown bats have a major impact on insect populations around their roosts.  It is the most common and widely distributed bat species in Alaska, yet overall population status and trends are unknown.  Little is known about their biology and ecology in Alaska.  Research is needed to assess reproductive success, foraging strategies, prey availability, habitat preferences, migration patterns, habitat usage, home range and hibernation ecology.  Threats include human disturbance, habitat loss due to deforestation and fragmentation, use of pesticides and use of cyanide in mining.  Primary predators include domestic cats, weasels, hawks, and other small carnivores.

Sources: (Animal Diversity Web) ADF&G New Hampshire Fish & Game