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Keen's Myotis (Myotis keenii)
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Did You Know?

Bats, though mammals, are not rodents. They are more closely related to primates than to rodents.

General Description

Keen's myotis is a medium-sized (wingspan 21–26 cm) insectivorous bat with dark silky brown fur and indistinct dark shoulder spots on the back. Their ear and flight membrane is dark, but not black. The ears are long enough to extend at least 4 mm beyond the tip of the nose when pressed forward. The tragus is long, upward pointing, and tapered at the end, in contrast with the short, blunt ended tragus of the little brown bat. The tragus is a fleshy projection that covers the ear canal, the entrance of the ear. (People have a tragus, too, but it doesn't play a role in echolocating as it does in bats). Because each species of bat has a different shaped tragus, this is a good way to identify them. The outside edge of the tail membrane has a fringe of tiny hairs, visible with a hand lens. Keen's myotis averages 9 cm in length and 8 grams in weight. Because of the relatively low number of M. keenii that have been captured in the wild, little information is known about their lifespan, but they have been documented to live up to 13 years.

Studies have shown that M. keenii prefer to roost in Cedar and Hemlock trees that have various degrees of decay and defects.

Life History

Growth and Reproduction

Little is known about the breeding habits of Keen's myotis. Limited evidence suggests that M. keenii mates in autumn and gives birth to a litter of one the following June or July.

Warm roost sites with stable microclimates are selected by females for day-roosting in temperate climates, which likely reduces the demands of thermoregulation. This assists reproductive females in fetal development and growth of juveniles by allowing reproductive females to avoid or reduce the use of torpor. Bats often enter torpor during inclement weather to conserve energy, but this delays juvenile and fetal development and inhibit milk production. Females provide milk and protection to their young until they become independent, usually by late August. Torpor occurs when M. keenii enters a decreased state of physiological activity by reducing their rate of metabolism and body temperature. Torpor can occur daily during winter months.

Feeding Ecology

Very little is known about this species. They are believed to be solitary and reported to fly rather slowly while foraging. Being nocturnal animals, bats sleep during the day and hunt and feed during the night on caddis flies, mayflies, leafhoppers, beetles, moths, lacewings, and spiders. The short duration of darkness during summer nights at high latitudes reduces foraging opportunities, thereby limiting the northern range of bats. M. keenii captures both flying prey in the air and by gleaning prey from surfaces. Studies have shown about half the M. keenii's diet to consist of spiders, suggesting that this species is actively selecting their prey by gleaning rather than opportunistically hunting.


Migration for M. keenii occurs between summer maternity colonies/foraging areas and hibernacula (where bats hibernate).

Range and Habitat

Distributional range suggests Keen's myotis is associated with coastal forest habitat. They are also associated with mature forests. Southeastern Alaska's temperate rainforests contain abundant live trees and snags in a variety of sizes. Such structural diversity provides loose bark and tree hollows suitable for cavity roosting bats, suggesting that the temperate rainforests of southeastern Alaska provide structure required by M. keenii and other bat species. Caves and crevices are also important habitat for this species, and over 1,769 km² of cave and crevice-containing karst occurs throughout southeastern Alaska. Myotis keenii has one of the most restricted distributions of any North American bat.

Status, Trends, and Threats


  • NatureServe: Global — G2G3 (Vulnerable)
  • IUCN: LC (least concern)


Statewide trends in population numbers are unknown, but presumably is at least several thousand. A maternity colony in British Columbia included about 40 reproductive females.


The distribution of M. keenii is associated with coastal rainforests in the Pacific Northwest. Forty-two percent of the most productive forests in southeastern Alaska were harvested by 1990, including over 70% of the karstland forests on Prince of Wales and neighboring islands. Current levels of timber harvest could have a detrimental effect on the Alaska population by altering forest structure important to bats. Bat activity is rare in clearcuts and second-growth forests of Southeast Alaska. Destruction of karst by recreationalists or mineral extraction may be a threat, as these areas are critical hibernacula.

Fast Facts

  • Size
    Length: 9 cm
    Weight: 8 g
    Wingspan: 21–26 cm
  • Range/Distribution
    Temperate coastal forests of Southeast Alaska
  • Diet
    Flying insects
  • Predators
    There are no documented predators of this species. It is likely the same animals that prey upon the little brown bat also take Keen's myotis, such as owls, hawks, cats, or raccoons.
  • Reproduction
    Only one litter, usually of a single pup, is produced per year.

Did You Know?

  • Bats, though mammals, are not rodents. They are more closely related to primates than to rodents.
  • Bats are in their own Order, called Chiroptera, meaning "hand-wing." This is due to their unique flight abilities with wing bones that are similar to those in human fingers.
  • Since the early 1970s, more than 150 bats in Alaska have been evaluated for rabies. Only two cases have been confirmed, a little brown bat found near Ketchikan in 1993 and a Keen's long-eared bat found on northeastern Prince of Wales in 2006.
  • Myotis keenii has one of the most restricted distributions of any North American bat.


In Alaska, bats are managed as a non-game species. Because some of the most productive forests in southeastern Alaska are on karst, this component of southeastern Alaska's rainforest system is especially important bat habitat. An adequate supply of roosting sites, foraging habitat, and other critical habitat should be maintained. However, due to the overall lack of information on this species' distribution in the state, it is impossible to identify specific areas and habitats used by this bat until a rangewide inventory is complete. Planning and environmental assessment processes for public lands should include such information when considering the effects of land-management practices.

Get Involved

Southcentral and Interior Alaska

It is easy to participate in the Alaska Bat Monitoring Program. We know very little about where bats occur in Southcentral or Interior Alaska during the summer, and no one knows what happens to them in winter. Alaska Bat Monitoring Volunteers help to document the presence and locations of bats and their habitats in preparation for future research. Visit the Alaska Bat Monitoring Program web page for more information.

Southeast Alaska

Little is known about the ecology of bats in Alaska. Their distribution and abundance during the summer months is poorly understood and few summer maternity roosts have been documented. Even less is known about where our bats go in the winter. The U.S. Fish and Wildlife Service listed the entire genus Myotis as a conservation concern in 2003 and a new disease, White Nose Syndrome, is decimating bat populations in eastern North America. Because bats occur in low densities in Alaska, documenting their summer distribution, roosting habitat, migration habits, and winter hibernacula is a challenging task. Through increased awareness of the value of bats in the wild and your reported bat sightings, we can slowly begin to understand and conserve bats in Alaska. It is important that we continue to learn more about bats and bat ecology in Southeast Alaska so we can conserve resources critical to their survival and prevent population declines.

  • Report Observations
    Help researchers document the distribution of bats in Southeast Alaska, collect bat carcasses for disease surveillance, locate roosts for monitoring, and learn more about bat use of bat houses in the region.
  • Roost Monitoring
    Help researchers document maternity colony size and timing of reproduction by volunteering to count bats as they emerge from their roost.
  • Acoustic Monitoring
    Help researchers study habitat relationships and relative abundance of bats by conducting an acoustic monitoring survey with a bat detector.

More Resources

General Information