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Myotis Keenii - Keen's Myotis


Keen’s Myotis is a smaller bat similar in size and appearance to the Little Brown Bat (Myotis lucifugus). It weighs between 6 to 9 grams with a wingspan 23 to 26 cm. It’s average length is 78 mm with a 26 mm long tail (Myers and Ollendorff, 2000). Keen’s Myotis has short brown fur on its body with dark patches on its shoulders. It has one claw on each thumb, a long rostrum. They also have small eyes and characteristic long complex ears (Canadian Biodiversity, 2000).


Myotis keenii can be found throughout Wisconsin most of North America from Manitoba across Southern Canada to Newfoundland, South to Florida, West though the Central States, with some isolated cases in southern Texas, and Northwest to the Dakotas. Myotis keenii primarily utilizes dense forest stands for their maternity roosts and hibernate in cooler stagnant air caves (Bat Conservation International Inc., 2002). One such hibernation cave in Wisconsin is the Bay City Mine (Wisconsin Department of Natural Resources, 2003).

Ontogeny and Reproduction:

Keen’s Myotis like most bats has only one pup per year. They typically birth their young in May or June after copulating and storing the male sperm in the fall. The sperm is stored through the hibernation period and then implanted after hibernation subsists beginning gestation lasting 50-60 days (Myers; Ollendorff, 2000). The young Myotis k. wean in a maternity colony for approximately 1 month. Maternity roosts are typically located in snags or cavities in or just bellow the canopy of hardwood forests (Menzel et. al. 2002). It has been observed that there is some crossover breeding between Myotis keenii and Myotis eutis (Van Zyllde Jong et. al. 1994).

Ecology and Behavior:

Myotis keenii is an insectivorous bat feeding on caddis flies, moths, beetles, flies, and leafhoppers emitting high intensity sonar when hunting most flying insects (Miller and Surlykke 2001). They provide a valuable role in pest control. Keen’s Myotis uses specialized Gleaning attacks, which allow them to passively listen and utilize a frequency of echolocation that cannot be heard by moths. (Myers; Ollendorff, 2000).  Other than in maternity roosts Myotis keenii is a fairly solitary and is most likely to be found alone, however, there are times when it can be found in groups of up to 100 individuals (Bat Conservation of Wisconsin Inc., 2001). At the end of summer Myotis keenii has been know to move of to 56 kilometers to hibernate, which they will do for 8-9 months.


It should be noted that Myotis keenii was, until recently, known as Myotis septentrionalis.

Literature Cited:

BAT Conservation of Wisconsin, Inc. 2001. “Northern Myotis.”  <>.

Bat Conservation International, Inc. 2002, “Myotis keenii.”  <>.

Canadian Biodiversity. 2000. “Canadian Biodiversity: Myotis keenii description.”  <>.

Menzel, et al. 2002. “Roost tree selection by northern long-eared bat (Myotis septentrionalis) maternity colonies in an industrial forest of the central Appalachian mountains.” Forest Ecology and Management 155: 107-114.

Miller, L.A. and A. Surlykke.  2001.  “How Some Insects Detect and Avoid Being Eaten by Bats: Tactics and Countertactics of Prey and Predator”, BioScience 51(7): 570-581.

Myers, P. and J. Ollendorff. 2000. “Myotis septentrionalis (Northern Bat, Keen’s Bat)”, Michigan Museum of Zoology.  <$narrative.html>.

Van Zyllde Jong, C.G. and D.W. Nagorsen.  1994.  “Myotis keenii/Myotis septentrionalis.”  Canadian Journal of Zoology 72: 1069-1078.

Wisconsin Department of Natural Resources. 2003.  “Bay City Mine State Natural Area (No. 280).”  <>.

Reference written by Mathew Rice, Biol 378: Edited by Chris Yahnke. Page last updated 4-28-04.

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