Myotis keeniiKeen's myotis

Geographic Range

Myotis keenii has one of the most restricted ranges of any temperate vespertilionid bat, being found only in the coastal forests of the Pacific Northwest, extending as far north as southeast Alaska, and reaching as far south as the state of Washington with the bulk of its range contained in British Columbia. This species of bat is restricted to warm maritime forests in which prey and roosting sites are abundant. Keen's bats may make small-scale movements to suitable hibernacula but do not migrate. (Chatwin, 2004; COSEWIC, 2003; Nagorsen and Brigham, 1993; Parker, et al., 1997)


The foraging environment for M. keenii is large coastal old growth forests in which prey density is sufficient. The preferred roosting habitat for this species includes the loose bark of large trees, caves, snags, hollow trees, and human made structures such as bridges and house attics. Myotis keenii is believed to hibernate or overwinter in caves, called hibernacula, found scattered about the coastal range these bats inhabit. Hibernacula are only known from caves in karst formations. Maternity roosts are known only from a hydrothermally heated system of rock crevices and a lodgpole pine snag (Pinus contorta). Since these bats are difficult to capture and there are only a few colonies that have been studied, many inferences about their ideal habitat and behavior have been made based only only a few observations. (Chatwin, 2004; COSEWIC, 2003; Lewis, 2000; Parker, et al., 1997)

  • Range elevation
    0 to 1100 m
    0.00 to 3608.92 ft

Physical Description

Myotis keenii is a medium sized vespertilionid with dark brown fur on its back, often with darker patches at the shoulders, and lighter fur on its underbelly. The ears, when laid forward, reach just beyond the nose and possess a long, slim pointed tragus. Ear length ranges from 13 to 20 mm. The ears, wings and uropatagium are a dark brown color, sometimes almost black, with the uropatagium possessing minute intermittent hairs at its edge. The calcar supporting the uropatagium generally lacks a conspicuous keel and the skull includes a steeper forehead than that of its close relatives, M. evotis and M. thysanodes. A large degree of overlap in external characteristics, such as forearm and ear length and pelage and membrane color, makes it impossible to distinguish M. keenii from its closely related congener, M. evotis. Myotis keenii is also easily confused with M. septentrionalis and M. lucifugus, as all have extensive overlap in external characteristics as well. Finally, the closely related M. thysanodes may be confused with M. keenii when the tail membrane is not conspicuously fringed. Reliable species identification may only be effected by genetic analysis or by analysis of cranial measurements. Myotis keenii has a wingspan ranging from approximately 20 to 26 cm, an overall length of 40 to 55 mm and an average weight ranging from 4 to 6 grams. There is no documented sexual dimorphism. (COSEWIC, 2003; Nagorsen and Brigham, 1993; van Zyll de Jong, 1985)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    4 to 9 g
    0.14 to 0.32 oz
  • Average mass
    6 g
    0.21 oz
  • Range length
    40 to 55 mm
    1.57 to 2.17 in
  • Range wingspan
    21 to 26 cm
    8.27 to 10.24 in
  • Average wingspan
    24.1 cm
    9.49 in


No information is available on the mating systems of M. keenii. Most temperate zone vespertilionids mate at hibernacula in the fall. Mating at hibernacula is often characterized by "swarming" and is likely to be indiscriminate. (Tuttle and Stevenson, 1982)

Only one study, the Gandl K’in Gwaayaay (Hotspring Island, Gwaii Haanas National Park) study, reports reproduction information for M. keenii in detail. However the colony studied is based out of a hydrothermal maternity roost that may provide information unrepresentative of other colonies of the same species due to the unique nature of the roost. Similar to other Myotis species, M. keenii are assumed to mate in autumn or early winter before entering hibernation, hold the sperm until spring, then ovulate and become pregnant upon their spring awakening. (Chatwin, 2004; COSEWIC, 2003)

Upon leaving the winter hibernacula, pregnant females will journey to maternity roosts in early summer (April or May) where they will stay until the young are born. Female M. keenii will produce one offspring per year after a relatively long gestation period of approximately 40 to 60 days. Newborn bats are generally capable of flight three weeks after birth but are not weaned until they are capable of fending for themselves, thus the young bats have a total rearing time of approximately five to six weeks. The young are believed to become sexually mature near the end of their first summer, or breeding season, but are not expected to breed until their second breeding season. (Chatwin, 2004; COSEWIC, 2003)

  • Breeding interval
    Myotis keenii breed annually just prior to hibernation.
  • Breeding season
    Mating occurs in autumn, in approximately the month of September.
  • Range number of offspring
    1 to 1
  • Average number of offspring
  • Range gestation period
    40 to 60 days
  • Range weaning age
    21 to 42 days
  • Average weaning age
    35 days
  • Range time to independence
    3 to 6 weeks
  • Average time to independence
    5 weeks
  • Average age at sexual or reproductive maturity (female)
    12 months
  • Average age at sexual or reproductive maturity (male)
    12 months

Female M. keenii provide nourishing milk and protection for their young until they are capable of flight and foraging on their own. At the end of the summer (August to September), when young have become independent, female M. keenii leave for their winter hibernacula. Growth in vespertilionid bat young is rapid, with young growing to adult size, attaining flight, training in the use of echolocation, and attaining independence within six weeks of their birth. Males are not involved in parental care. (Chatwin, 2004; COSEWIC, 2003)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


Little information on the longevity of M. keenii is available. Recapture records from the Gandl K’in Gwaayaay (Hotspring Island) study show a maximum documented recapture age of 12 years and 11 months. This is believed to be an underestimate of total lifespan since other Myotis species have documented life spans of 13 to 22 years. (COSEWIC, 2003)

  • Range lifespan
    Status: wild
    13 (high) years
  • Average lifespan
    Status: captivity
    19 years


M. keenii appears, by all accounts, to be a social creature. Studied maternity roosts have been approximated at 30 to 40 females, and hibernacula have similarly been documented as the residence for large colonies of bats, even incorporating other species of bat. They are nocturnal, but may be active at dusk and dawn. Myotis keenii hibernates during the winter and becomes torpid during daytime roosting. ("Bats in Alaska", 2001; Chatwin, 2004; COSEWIC, 2003; Ministry of Environment, Lands and Parks Resources Inventory Branch, 1998; Parker, et al., 1997)

Home Range

This species of bat tends to stay relatively close to favored roosting sites and from the limited studies and accounts involving M. keenii the estimated daily travels are less than 1 km. Evidence that these bats return to specific foraging areas year after year has also been documented although their specific roosting and foraging range sizes have not been determined. It has also been suggested that M. keenii may make short migrations between summer ranges and hibernacula. (Chatwin, 2004; COSEWIC, 2003)

Communication and Perception

Communication specifics are not well understood for M. keenii. Vespertilionid bats have well-developed vision, but to what extent vision is used is unknown in M. keenii. Myotis keenii have very accurate echolocation, coupled with capability of highly maneuverable flight, that allows them to fly in adverse weather as well in dense forests, which other bat species seem to avoid. This also gives them the ability to detect and glean prey that are stationary on trees, leaves, and rocks. Unfortunately, for researchers, this also makes them rather difficult to capture using standard mist net and harp trap techniques, and subsequently, hard to study. Whether this species uses their sense of smell extensively has not been tested although it is reasonable to assume they use their sense of smell in offspring recognition as in other mammals. ("Bats in Alaska", 1986; Chatwin, 2004; COSEWIC, 2003; Ministry of Environment, Lands and Parks Resources Inventory Branch, 1998; Parker, et al., 1997)

Food Habits

Foods of choice for M. keenii include: spiders, caddis flies, mosquitoes, flies, moths, midges and other assorted flying insects. Having a prey base that includes flying and non-flying prey is thought to give the bats flexibility with respect to environmental conditions that may be adverse for catching certain types of prey. Although M. keenii is adept at catching flying insects, the preferred source of food appears to be spiders and Lepidoptera which, in the Gandl K’in Gwaayaay (Hotspring Island) study, were present in approximately 78% of the pellet material obtained from maternity roosts. Prey choice is likely dependent on prey abundance. ("Bats in Alaska", 2001; Chatwin, 2004; COSEWIC, 2003; Ministry of Environment, Lands and Parks Resources Inventory Branch, 1998)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods


Actual predation information for M. keenii is not available although bats of the Vespertilionidae family in general are thought to fly mainly in darkness to maximize predator avoidance. Expected predators are owls, hawks, cats, raccoons, snakes, and some carnivorous rodents, such as Peromyscus spp., that are a threat to bats while roosting. (COSEWIC, 2003)

Ecosystem Roles

Since low numbers of Myotis keenii have been captured, the current assumption is that the overall species numbers are low. This would lead one to believe that M. keenii is not a significant prey item for either predatory raptors or terrestrial predators. However, despite their low numbers, their specialization on moth prey makes them potentially important predators of moths in the areas in which they live. (Chatwin, 2004; COSEWIC, 2003)

Economic Importance for Humans: Positive

Most bats of the family Vespertilionidae consume insects, many of which are potential pest species. Small populations of bats can consume vast quantities of insects thus controlling pest insect populations. (Chatwin, 2004; COSEWIC, 2003)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Bats, along with all other mammals, are capable of harboring and transmitting the rabies virus, as well as the possibility of carrying Salmonella spp., Toxoplasmosis gondii, and Ebola virus. No M. keenii individuals, and few bats, have been implicated in the transmission of these diseases. ("Bats in Alaska", 2001)

Conservation Status

Due to the severe lack of information about basic life history, distribution, and population status of this species, it is on the British Columbia Red List and has a provincial rank of S2 (imperiled). British Columbia has also classified M. keenii as an identified wildlife species under the BC Provincial Forest and Range Practices Code (COSEWIC, 2003). This enables the management of the species and allows for establishment of Wildlife Habitat Areas (WHA) that defines no-disturbance perimeters around hibernacula, maternity sites, and roosting sites.

Myotis keenii is a state candidate species in Washington and is considered state sensitive in Alaska. It is not included in the IUCN Red List, CITES appendices, or the U.S. Endangered Species Act. (COSEWIC, 2003; Government of British Columbia, 2003)

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Myotis keenii mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Other Comments

Myotis keenii was previously considered conspecific with Myotis septentrionalis, which was recognized as a distinct species by van Zyll de Jong in 1979. It is now understood that M. keenii is closely related to M. evotis and M. thysanodes, and is only distantly related to M. septentrionalis> (COSEWIC, 2003; Nagorsen and Brigham, 1993; van Zyll de Jong, 1985)


Joe Filla (author), University of Alaska Fairbanks, Link E. Olson (instructor), University of Alaska Fairbanks, Tanya Dewey (editor), Animal Diversity Web.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


uses smells or other chemicals to communicate


active at dawn and dusk

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.


The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


makes seasonal movements between breeding and wintering grounds


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


uses sound above the range of human hearing for either navigation or communication or both


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


State of Alaska, Department of Fish & Game. Bats in Alaska. Vol. 18, No. 4 (July-Aug. 1986) p. 20. Anchorage, Alaska: State of Alaska, Department of Fish & Game. 1986.

State of Alaska, Section of Epidemiology. Bats in Alaska. Bulletin No. 16. Anchorage, Alaska: State of Alaska, Section of Epidemiology. 2001. Accessed November 29, 2004 at

COSEWIC, 2003. "COSEWIC assessment and update status report on Keen's long-eared bat Myotis keenii in Canada." (On-line pdf). Government of Canada: Species At Risk Act Public Registry. Accessed November 24, 2004 at

Chatwin, T. 2004. "Keen's Long-eared Myotis" (On-line pdf). British Columbia Ministry of Water, Land & Air Protection. Accessed November 24, 2004 at

Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at

Government of British Columbia, 2003. "BC Species and Ecosystems Explorer" (On-line). Accessed December 09, 2004 at

Hall, R. 1981. Mammals of North America, 2nd Ed., Vol. 1. New York, New York: John Wiley & Sons, Inc..

Lewis, S. 2000. Roosting and Hibernal Ecology of Bats in Southeast Alaska's Karstlands. The Alaskan Caver, Vol. 20, No. 4: 1 to 6.

Ministry of Environment, Lands and Parks Resources Inventory Branch, 1998. "Inventory Methods for Bats" (On-line pdf).

Inventory Methods for Bats : Standards for Components of British Columbia's Biodiversity No. 20
. Accessed November 24, 2004 at

Nagorsen, D., R. Brigham. 1993. The Bats of British Columbia. Vancouver, BC: UBC Press, University of British Columbia.

National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at

Parker, D., B. Lawhead, J. Cook. 1997. Distributional Limits of Bats in Alaska. Arctic, Vol. 50, No. 3: 256-265.

Tuttle, M., D. Stevenson. 1982. Growth and Survival of Bats. Pp. 105 to 149 in T Kunz, ed. Ecology of Bats. New York, USA: Plenum Press.

van Zyll de Jong, C. 1985. Handbook of Canadian Mammals, Vol. 2. Ottawa, Canada: National Museums of Canada.