Myotis septentrionalis (Trovessart, 1897)
Northern Long-eared Bat
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Basis for Listing
The Northern Long-eared Bat (Myotis septentrionalis), also known as the Northern Myotis, is widely distributed in Canada and throughout the eastern half of the United States. It was designated a species of special concern in Minnesota in 1984, at which time it was known from only a few widely distributed localities in the state. Subsequent survey work has documented additional locations in Minnesota and confirmed that the species can be found in the state in both summer and winter. A large hibernating population was documented in St. Louis County, and Northern Long-eared Bats have been found in many other caves and mines surveyed in Minnesota, though typically in low numbers.
The spread of white-nose syndrome (WNS) across the eastern portion of the United States has become the major threat to the Northern Long-eared Bat. White-nose syndrome is caused by the fungus (Pseudogymnoascus destructans), which thrives in cave environments. The fungus is believed to cause cave bats to arouse from hibernation, subsequently depleting stored body fat, often leading to emaciation and death (Frick et al. 2010). The syndrome is associated with high mortality in bat hibernacula, with some sites documenting up to 90 or 100 percent mortality (Lankau and Rogall 2016). The fungus was first documented in Minnesota during winter 2011-2012, and the presence of the disease was confirmed during winter 2015-2016. Declines in the number of hibernating Northern Long-eared Bats as great as 100% were observed in Minnesota’s hibernacula in 2017, following the second year of WNS infection.
Human disturbance in caves occupied by Northern Long-eared Bats, wind turbine-caused mortalities, and habitat loss are other potential threats. Northern Long-eared Bats were designated as a federally threatened species by the U. S. Fish and Wildlife Service in April 2015 and remain listed as a special concern species in Minnesota. A list of all townships containing known Northern Long-eared Bat roost trees and/or hibernacula in Minnesota is available.
The Northern Long-eared Bat is a medium-sized bat, with relatively long ears with a long sharply pointed tragus (fleshy projection in the ear). The pelage is dull brown on the back and pale grayish brown on the underside. The membranes are dark, and the calcar (a bone or cartilage growth from the ankle that helps to support the tail membrane in flight) is slightly keeled. Adults typically measure 7.8-9.5 cm (3.1-3.7 in.) in total body length, with a tail length of 3.2-3.4 cm (1.2-1.3 in.). Weights range from 5.0-6.4 g (0.18-0.23 oz.) (Hazard 1982). The Northern Long-eared Bat can be distinguished from the Little Brown Myotis (Myotis lucifugus) by its long ears and pointed tragi. When folded forward, the Northern Long-eared Bats’ ears extend at least 3 mm (0.12 in.) beyond its nose. The ears of the Little Brown Myotis, on the other hand, are even with or only barely extend past the tip of the nose, and the tragi are shorter and blunted.
Northern Long-eared Bats have been found in the winter in Minnesota in natural caves, sand mines, and iron mines. Hibernacula are shared between both sexes and often multiple species of bats. Preferred sites typically have high humidity levels, minimal airflow, and a constant temperature (Fitch and Shump 1979). After spring emergence, bats migrate to summer roosting and foraging grounds. In summer, the species is often associated with forested habitats (Fire-Dependent Forests, Mesic Hardwood Forests, and Floodplain Forests) where they make use of tree roosts, especially near water sources. Loose bark, broken tree limbs, cavities, and cracks in a tree can all be utilized by bats as roosting sites. The sexes tend to roost separately, with females forming small (~30 individuals) maternity colonies to bear and rear their offspring. Males often roost alone, as they do not have the same high temperature needs as maternity colonies.
Biology / Life History
Northern Long-eared Bats enter their winter hibernacula from late August through September. They typically roost singly or in small groups (Nordquist and Birney 1985). Emergence from the hibernaculum takes place during May. Bats in the family Vespertilionidae ('vesper bats' or 'evening bats') display delayed fertilization, where mating takes place in fall, ovulation and fertilization do not occur until spring. Females bear a single offspring in June or July. The earliest-born young are usually able to fly by early July, and the nursery colonies disband around this time. Northern Long-eared Bats forage for insects over water, in forest clearings, and under tree canopies, using echolocation to catch prey and to navigate. They may also glean insects off leaves and other surfaces, a behavior that may be aided by their unusually large ears. Foraging takes place throughout the night, peaking before midnight and again just before sunrise (Laubach et al. 1994).
Conservation / Management
The appearance of WNS in 2006 resulted in unprecedented mortality among 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 about the fungus and 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). Although much has been learned about the disease since onset, a cure or method of preventing the fungus from entering other hibernacula is as yet unknown.
Gaps in knowledge about the Northern Long-eared Bat have also inspired state projects focused on the ecology of the species, which can vary by region. Winter hibernacula surveys document trends in hibernating populations and assess the health of these bats. As a species that utilizes trees during summer, retention of roost trees in a variety of decay classes provides critical habitat for recovery from the disease and successful reproduction.
Conservation Efforts in Minnesota
The Minnesota DNR’s Minnesota Biological Survey has been monitoring the health of hibernating bats since 2010. Collaborating with national research projects addressing the spread and possible control of WNS, the Minnesota DNR continues to provide information on the status of Northern Long-eared Bats through winter hibernacula surveys, summer acoustic surveys, and targeted population assessments Education about the importance of bats and effects of WNS is also a component of conservation efforts.
The Minnesota Environmental and Natural Resources Trust Fund provided support for a cooperative partnership between the Minnesota Department of Natural Resources, the University of Minnesota Natural Resources Research Institute, and the U.S. Forest Service to assess critical summer habitat for Northern Long-eared Bats in the state. Information collected about roosts, colony trees, and stands will inform forest management recommendations to ensure adequate roost and foraging habitat for the Northern Long-eared Bat.
Gerda E. Nordquist, 1988; Jeanine Refsnider, MN DNR, 2008; Melissa Bowman, MN DNR, 2017
Fitch, J. H., and K. A. Shump, Jr. 1979. Myotis keenii. Mammalian Species 121:1-3.
Foster, R.W., and A. Kurta. 1999. Roosting ecology of the Northern Bat (Myotis septentrionalis) and comparisons with the endangered Indiana Bat (Myotis sodalis). Journal of Mammalogy 80(2):659-672.
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.
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>.
Laubach, C. M., J. B. Bowles, and R. Laubach. 1994. A guide to the bats of Iowa. Iowa Department of Natural Resources. Des Moines, Iowa. 33 pp.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia.
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.
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.
U.S. Forest Service. 2000. Population viability assessment in forest plan revision. Questions for animal population viability assessment panel: Myotis septentrionalis. United States Forest Service, Region 9, Duluth, Minnesota.
U.S. Geological Survey. 2016. White-nose syndrome (WNS) [web page]. National Wildlife Health Center, USGS. <www.nwhc.usgs.gov/disease_information/white-nose_syndrome/>.