Myotis septentrionalis (Trovessart, 1897)
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Basis for Listing
The northern myotis, also known as the northern long-eared 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 hibernaculum was discovered in St. Louis County, and northern myotis have been found in most other caves and mines surveyed in Minnesota, although typically in low numbers.
The northern myotis is a medium-sized bat with relatively long ears, each 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 (bone or cartilage growth from the ankle that helps to support the tail membrane in flight) is slightly keeled. Adults typically measure 78-95 mm (3.1-3.7 in.), with a tail length of 32-34 mm (1.2-1.3 in.). Weights range from 5-6.4 g (0.18-0.23 oz.) (Hazard 1982). The northern myotis can be distinguished from the little brown bat by its long ears, which, when folded forward, extend at least 3 mm (0.12 in.) beyond its nose. The ears of the little brown bat, on the other hand, are even with or only barely extend past the tip of the nose.
Northern myotis have been found in the winter in Minnesota in natural caves, sand mines, and deep iron mines. They seem to prefer cool, moist hibernating sites where the air is still (Fitch and Shump 1979). Farther south, northern myotis may also use attics, bridges, and buildings. In summer, the species is often associated with forested habitats, especially around wetlands. Summer roosts are believed to include separate day and night roosts. Day roosts may be under loose tree bark, in buildings, or behind signs or shutters, and night roosts may include caves, mines, and quarry tunnels (summarized in NatureServe 2008). The sexes tend to roost separately, with females forming small (~30 individuals) maternity colonies in relatively warm sites to bear and rear their offspring.
Biology / Life History
Northern myotis enter their winter hibernacula in late August or September. They are colonial hibernators, but rarely occur in concentrations of over 100 individuals. Most frequently, they are found hanging singly or in small groups (Nordquist and Birney 1985). Emergence from the hibernaculum takes place in May. Bats in the family Vespertilionidae display delayed fertilization, where mating takes place in fall but embryo implantation does 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 myotis forage for insects over water and 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 its unusually large ears. Foraging takes place throughout the night, but peaks before midnight and again just before sunrise (Laubach et al. 1994).
Conservation / Management
Winter populations of northern myotis should be surveyed annually at all known hibernacula, especially the large underground mine in St. Louis County (Nordquist et al. 2006). If possible, hibernacula should be protected from disturbance, as any human activity in a hibernaculum can drastically and negatively affect the status of hibernating bats. Foster and Kurta (1999) found that the number of different trees used for roosting was directly correlated with the duration of tracking. Therefore, retention of diverse native forests is likely important for this species, especially in agricultural areas where forests are often young and widely dispersed. However, forest structure and age class of trees appear to be more important habitat components than the type of tree for the northern myotis, so maintenance of older trees is important when managing for this bat (U.S. Forest Service 2000).
Conservation Efforts in Minnesota
The DNR's Nongame Wildlife Program and the State Wildlife Grants Program have funded several projects to census bats hibernating in caves and mines throughout the state. Several of the known northern myotis hibernacula are located in State Parks and receive adequate protection. Attempts are being made to work with landowners of privately owned hibernacula sites to protect hibernating bats.
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.
Hazard, E. B. 1982. The mammals of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 280 pp.
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. 18 pp.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. <http://www.natureserve.org/explorer>. Accessed 9 June 2008.
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. 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.