Species spotlight: Little brown bat

Common name: Little brown bat
Scientific name: Myotis lucifugus
Size: Averages 2.5 to 4 inches in total length from nose to tail, with a tail length of 1.2 to 1.6 inches. The wingspan of little brown bats ranges from 8 to 11 inches. Females are typically slightly larger than males.
Range: Little brown bats are found across the United States, north into southern Alaska and Canada, and south into the higher elevation forests of Mexico. Across the northern part of their range, they were historically the most abundant bat species. They were also common across much of the south, though absent from parts of southern California, the Great Plains, Florida, and coastal North Carolina and Virginia. 
MA conservation status: Endangered
Federal conservation status: Not listed

• Little brown bats are insectivores and a single bat can consume up to 1,000 insects in an hour. A pregnant female can eat up to her entire body weight in insects each night. Before hibernation, little brown bats eat more to prepare for the cold weather and increase their body weight by over 30%.

• During the winter, little brown bats hibernate, enduring temperature fluctuations of up to 120°F without negative consequences. During this time, their heartbeat drops to as low as 8 beats per minute compared to a rate of up to 1,300 beats per minute while in flight in the summer. 

• Little brown bats use self-generated, high-frequency sounds and a type of natural sonar called echolocation to locate prey and avoid collisions. Individuals can emit up to 20 calls per second while flying and up to 200 calls per second when closing in on prey. 

• In the summer, females rear the pups and live separately from the males. Once winter approaches, the males and females reunite and hibernate together.  

• In order to save energy, little brown bats sleep about 20 hours a day on average.  

• Little brown bats are nocturnal, meaning they are active at night and emerge from their roosts at dusk to forage until dawn, taking small breaks to rest and digest their meals. 

• Little brown bats have several different types of roost sites: day roosts, which are typically caves, mines, trees, under rocks, or buildings; night roosts, which are similar to day roosts, but separate to protect the bats from predators; nursery roosts, which are larger and warmer than day roosts found in large tree hollows and buildings; and winter roosts, or hibernacula, which are abandoned mines and limestone caves. 

• Little brown bats can fly up to 22 miles per hour, but typically average about 12 miles per hour.  

• Little brown bats have a long lifespan compared to other small mammals. The average lifespan is  6–7 years, with one individual captured in the wild at 31 years old. 

Worldwide, bats face a variety of threats, largely the result of human activity.

• White-nose syndrome: The number one cause for the decrease in the local bat population is White-nose Syndrome (WNS), which is the result of an aggressive fungus that irritates and damages the skin, leads to dehydration, compromises immune systems, increases metabolism, and rouses bats from hibernation in the middle of the winter causing them to use up their precious fat reserves too quickly leading to starvation. For more information on White-nose syndrome, please see Bat Mortality in Massachusetts.  

• Habitat loss and degradation: Bats seek shelter under the peeling bark of dead trees. Little brown bats are threatened with the loss of their natural habitat as a result of deforestation. 

• Pesticide use: Pesticides weaken bats, contaminate drinking water, reduce food availability, and directly poison bats.  

• Climate change: Climate change influences hibernation timing, migration patterns, biogeography, access to food, reproduction and development, and echolocation abilities. 

• Wind turbines: With the rapid expansion of wind power, migrating bats collide with the spinning blades of turbines causing high mortality. Bats also suffer from extreme changes in air pressure close to turbines which causes a lung injury called barotrauma. 

• Fear: Bats are one of the most misunderstood animals, and this can cause people to intentionally harm bats and their habitats. 

• All five of the most important bat hibernacula in Massachusetts are now closed to public access to protect the few surviving bats from disturbance. MassWildlife has been conducting winter population counts of hibernating bats for over 40 years. Biologists carefully enter the mines and caves in late winter to identify species, count individual bats, and check body conditions for signs of WNS. In 2016-2018, MassWildlife hired contractors to conduct statewide surveys of bats using acoustics, mist netting, radio telemetry, emergence counts, and roost monitoring to determine the extent and distribution of Little brown bats in Massachusetts and to locate additional maternity colonies that could be monitored and protected.  

• Be a citizen scientist and spread the word about reporting colonies of 10 or more bats to MassWildlife using this form.  

• You can help dispel myths and fears about bats and help others learn why bats are beneficial. 

• Create a bat-friendly landscape in your backyard by installing a bat house (see MassWildlife's Guide to Bat Houses for more information), adding water features, such as a pond, planting night-blooming flowers, and leaving old and dying trees (if it's safe to do so) to be used as potential alternative roost sites.

• If you need to exclude or evict bats from your home, ensure the process is safe and humane by following MassWildlife’s recommendations found in the Massachusetts Homeowner’s Guide to Bats.  

• Reduce pesticide use to ensure bats have a reliable and safe food source.  

• Avoid disturbing hibernating bats by staying out of caves and mines where bats are hibernating in the winter.  

• MassWildlife's Natural Heritage and Endangered Species Program is responsible for the conservation and protection of over 400 rare animals and plants, including little brown bats. This work is primarily funded through grants and donations from supportive citizens. Support rare species conservation in Massachusetts—donate today!