Myotis lucifugus (Le Conte, 1831)
Little Brown Myotis
Basis for Listing
The Little Brown Myotis (Myotis lucifugus) is widely distributed throughout North America, from Alaska and Canada to Mexico. It is one of Minnesota’s four species of cave-hibernating bats and the most common of the state’s seven bat species. Secure winter roost sites, where the Little Brown Myotis spends nearly half of each year, are critical to the survival of the species.
Although bat populations have been relatively stable in past years, the emergence of a fungal disease has put previously common species at risk of regional or global extinction (Maslo et al. 2015). Bat white-nose syndrome is a devastating disease affecting cave-hibernating bats, caused by the fungus Pseudogymnoascus destructans. The syndrome is associated with high mortality in bats, with some sites documenting up to 90 or 100 percent mortality (Lankau and Rogall 2016). Hibernating bats observed to be affected by WNS display abnormal behaviors, such as daytime flights and clustering at the opening of the cave. These behaviors may result in stored body fat being depleted, with subsequent emaciation and death (Frick et al. 2010b). White-nose syndrome first appeared in New York State in the winter of 2006. Since then, it has spread at an alarming rate across North America and was confirmed in Minnesota by winter 2015-2016. Due to the slow reproduction rate of the Little Brown Myotis, it is unlikely the species will recover quickly from this sudden and widespread mortality. While federal and state agencies are taking steps to slow or control the spread of WNS, its anticipated profound impact on cave-hibernating bats led to the listing of the Little Brown Myotis as a special concern species in 2013.
Little Brown Myotis is a medium-sized bat, measuring 8.3-9.1 cm (3.3-3.6 in.) total length. Adults typically weigh 7-10 g (0.3-0.4 oz.) (Fenton and Barclay 1980). They have glossy fur that ranges from dark brown to olive brown on the dorsal side, transitioning to a lighter hue on the ventral side. Wing membranes, ears, and snout are dark brown. Little Brown Myotis can be confused with a few other species in Minnesota, including the Northern Long-eared Bat (Myotis septentrionalis) and the Tricolored Bat (Perimyotis subflavus). Little Brown Myotis have relatively short ears, with a blunt and rounded tragus (fleshy projection in the ear), in contrast to the Northern Long-eared Bats’ longer ears and sharply pointed tragus. Tricolored Bats can be distinguished by their light-colored arms and their tricolored pelage - bases and tips are dark, middle section is light.
Season, sex, and reproductive status influence Little Brown Myotis’ habitat use throughout their range (Frick et al. 2010a). This species is a cave-hibernating bat, which means during winter they seek caves, cellars, tunnels, and other underground structures. These structures typically have high humidity levels, minimal airflow, and a constant temperature (Fitch and Shump 1979). Hibernacula are shared by both sexes of multiple bat species. In the spring, bats emerge from hibernacula and migrate to summer roosting/foraging grounds. During summer, Little Brown Myotis commonly use human structures such as bridges, buildings, and attics but are also associated with forested habitats (fire-dependent forests, mesic hardwood forests, and floodplain forests) near water (Kunz 1982), where reproductive females will roost together in tree snags, under loose tree bark, and in cavities. These maternity colonies prefer hot and humid roosting sites in which to give birth and rear pups. (Kerth 2008). Males tend to roost alone, as they do not have the same temperature needs as a maternity colony. Old-growth forest is often chosen over young-growth, likely due to a higher presence of snags and decomposing trees (Owen et al. 2002).
Biology / Life History
Little Brown Myotis begin seeking out hibernation sites in the early fall. During this time, bats gather at openings of underground sites in a behavior known as “swarming”. This behavior is thought to facilitate a promiscuous mating system and provide an assessment of the hibernacula (Schaik et al. 2015). During winter, bats remain in a hibernation state known as “torpor” to conserve energy resources and fat. While mating occurs during swarming, ovulation and fertilization do not occur until bats emerge in the spring (Fenton and Barclay 1980). Females give birth to a single pup in June or July. During this time, they roost in maternity colonies consisting of only females and pups, due to high temperature needs. The colony disbands when the young begin to fly, typically three weeks after birth (Krochmal and Sparks 2007). Bats use echolocation for foraging and spatial navigation; they emit tonal signals that reflect off directed targets (Schnitzler et al. 2003). The return echoes detect, localize, and identify the reflecting object. This allows them to forage throughout the night for flying insects in forest corridors, clearings, and over water, such as streams and lakes.
Conservation / Management
The appearance of WNS in 2006 caused unprecedented mortality in hibernating bats in the northeastern U.S.. The ability of the disease causing fungus (Pseudogymnoascus destructans) to spread rapidly prompted immediate action for research and monitoring. In 2008, a coordinated effort was made by the Department of Interior, Department of Agriculture, Department of Defense, and state wildlife management agencies to develop an effective national response to the disease. Elements of the plan included research on the fungus and monitoring of affected bat populations, education on the fungus and the ecological importance of bats, reduction of environmental transmission to and from bats, and evaluation of the ecological and economic consequences of WNS (U.S. Fish and Wildlife Service 2011). While much has been learned about the disease since onset, there are still gaps in knowledge, and a cure or method of preventing the fungus from entering other cave systems is as yet unknown.
Given the high mortality rates bats are experiencing in the face of white-nose syndrome (WNS), it is necessary to protect important habitats and mitigate potential impacts for this species. Mature trees utilized by bats for maternity colonies need protection and preservation as successful reproduction will be critical in preserving bat populations affected by WNS. While Little Brown Myotis use a range of tree species in varying decay stages, they all share the characteristic of large diameters (Kalcounis 1996). Bats use multiple trees during the summer breeding season. These large trees, both dead and alive, are valued as lumber or other wood products and often removed from the landscape. It is important their value to bats as well as other species is recognized.
Conservation Efforts in Minnesota
The confirmation of WNS in Minnesota during the winter of 2015-2016 has led to increased concern for hibernating bats residing in the state. The Minnesota DNR’s Minnesota Biological Survey (MBS) has been monitoring the health of hibernating bats since 2010. Collaborating with national research projects addressing the spread and possible control of white-nose syndrome, the MBS continues to gather information on the status of Little Brown Myotis through winter hibernacula surveys, summer acoustic surveys, and targeted population assessments. Education on the importance of bats and the effects of WNS is also a component of conservation efforts.
Melissa Boman (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Fenton, M. B., and R. M. R. Barclay. 1980. Myotis lucifugus. Mammalian Species 142:1-8.
Fitch, J. H., and K. A. Shump, Jr. 1979. Myotis keenii. Mammalian Species 121:1-3.
Frick, W. F., D. S. Reynolds, and T. H. Kunz. 2010. Influence of climate and reproductive timing on demography of little brown myotis Myotis lucifugus. Journal of Animal Ecology 79(1):128-136.
Frick, W. F., J. F. Pollock, A. C. Hicks, K. E. Langwig, D. S. Reynolds, G. G. Turner, C. M. Butchkoski, and T. H. Kunz. 2010. An emerging disease causes regional population collapse of a common North American bat species. Science 329:679-682.
Hazard, E. B. 1982. The mammals of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 280 pp.
Kerth, G. 2008. Causes and consequences of sociality in bats. BioScience 58(8):737-746.
Krochmal, A. R., and D. W. Sparks. 2007. Timing of birth and estimation of age of juvenile Myotis septentrionalis and Myotis lucifugus in west-central Indiana. Journal of Mammalogy 88(3):649-656.
Kunz, T. H. 1982. Roosting ecology of bats. Pages 1-55 in T.H. Kunz, editor. Ecology of bats. Plenum Press, New York, New York. 450 pp.
Lankau, E. W., and G. M. Rogall 2016. White-nose syndrome in North American bats ? U.S. Geological Survey updates: U.S. Geological Survey Fact Sheet 2016-3084. 4pp. <https://pubs.usgs.gov/fs/2016/3084/fs20163084.pdf>.
Maslo, B., M. Valent, J. F. Gumbs, and W. F. Frick. 2015. Conservation implications of ameliorating survival of Little Brown Bats with white-nose syndrome. Ecological Applications 25(7):1832-1840.
Nordquist, G. E., and E.C. Birney. 1985. Distribution and status of bats in Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 64 pp.+ illustrations.
Nordquist, G. E., K. A. Lynch, and C. A. Spak. 2006. Timing and pattern of bat activity at Soudan underground mine. Final report submitted to the State Wildlife Grants Program, Minnesota Department of Natural Resources. 86 pp.
Owen, S. F., M. A. Menzel, W. M. Ford, J. W. Edwards, B. R. Chapman, K. V. Miller, and P. B. Wood. 2002. Roost tree selection by maternal colonies of northern long-eared myotis in an intensively managed forest. Northeastern Forest Experiment Station, USDA Forest Service. General Technical Report NE-292, Newtown Square, Pennsylvania. 6 pp.
Rogall, G. M., and M. Verant. 2012. White-nose syndrome in bats: U.S. Geological Survey updates. U.S. Geological Survey Fact Sheet 2012-3076.
Rysgaard, G. N. 1942. A study of the cave bats of Minnesota with especial reference to the large brown bat, Eptesicus fuscus fuscus (Beauvois). American Midland Naturalist 28(1):245-267.
Schnitzler, H. U., C. F. Moss, and A. Denzinger. 2003. From spatial orientation to food acquisition in echolocating bats. Trends in Ecology and Evolution 18(8):386-394.
Szymanski, J. A., M. C. Runge, M. J. Parkin, and M. Armstrong. 2009. White-nose syndrome management: report on structured decision making initiative. U.S. Fish and Wildlife Service, Fort Snelling Minnesota. 51 pp.
U.S. Fish and Wildlife Service. 2011. A national plan for assisting states, federal agencies, and tribes in managing white-nose syndrome in bats, USFWS, Hadley, Maryland. 21 pp.
van Schaik, J., R. Janssen, T. Bosch, A. J. Haarsma, J. J. A. Dekker, and B. Kranstauber. 2015. Bats swarm where they hibernate: compositional similarity between autumn swarming and winter hibernation assemblages at five underground sites. PLoS ONE 10(7):e0130850.