Myotis ciliolabrumwestern small-footed myotis

Geographic Range

Western small-footed bats (Myotis ciliolabrum) are commonly located on the western coastal regions of the Nearctic. In the Pacific northwest, western small-footed bats can be found in southern Saskatchewan, British Columbia, and Alberta. The range extends into the U.S. and northern Mexico along the western coast. Western small-footed bats can also be found in the Little Rocky Mountains located in north central Montana. Western small-footed bats are usually found nearby rivers as their distribution relies heavily on insect density. Two subspecies of western small-footed bats Myotis ciliolabrum exist in isolated regions; Myotis ciliolabrum ciliolabrum lives solely in Alberta and Saskatchewan, and Myotis ciliolabrum melanorhinus lives in British Columbia. (Ramsey, 1995)


Western small-footed bats are commonly found near sources of water with a large insect population. Elevation of selected habitats ranges from 300 to 3300m above sea level. These bats are unique in that they do not roost in trees, inhabiting cliff faces and rocky outcroppings no further than 2km away from their foraging grounds. In the summer, western small-footed bats will change their roost sites to crevices and cavities in cliff faces to escape the sun and heat. They also use human-made structures like buildings (e.g., abandoned houses), bridges, caves, and mines.

During the day western small-footed bats tend to roost alone, changing roost sites regularly within a small area of roughly 200m in diameter. During the night, the roost sites change to a small communal roost, possibly to increase the warmth of the roost. These night roost sites are generally found close to their foraging grounds. Steep valleys and cliffs tend to have a larger density of bats including western small-footed bats. These bats rely so heavily on sources of water (rivers or streams), they nocturnally forage within 1km of waterbodies.

These bats hibernate is small cracks and crevices in caves, with typically no more than 6 members of the species in one cave. These hibernate alone, not in clusters. (Downey, 2004; Holloway and Barclay, 2001)

  • Aquatic Biomes
  • rivers and streams
  • Range elevation
    300 to 3300 m
    984.25 to 10826.77 ft

Physical Description

Western small-footed bats are flying creatures that have wings made of a stretched membrane called a patagium. Western small-footed bats, on average, have a total height of 87.3mm (including ears; range 81-93mm). Wingspan ranges from 205-245mm, and ear length is 11-16mm, with the narrow tragus being about half the total ear length. On average, western small-footed bats have a mass of 5.88g (range 4.7-7.0g). In some, but not all, individuals, the tails protrude 1.5-2.0mm beyond the uropatagium (membrane), distinguishing them from closely-relates species. Foot lengths are about 9mm, and forearm lengths are typically below 34 mm. These bats' calcar is keeled. Their dental formula is 2133/3133, with 38 teeth in sum.

Sexual dimorphism has been suggested in western small-footed bats, as females can be larger than males. Bat weights in Nevada reported that females averages 4.7g, while males were just 4.0g. Further, bats in the southern portion of the range are larger than those in the northern end of the range.

These bats have a black mask on their face, and their ears and forearms also are dark. Their pelage is yellow or buff-colored, depending on the subspecies. Myotis ciliolabrum ciliolabrum exhibits a much lighter pelage (sometimes white on the ventral side) than Myotis ciliolabrum melanorhinus.

Pups are born fur-less, weighing about 1.1 to 1.6g. Anecdotal measures have reported neonates with forearm lengths of 12.4m and total lengths of 20mm. (Constantine, 1998; Holloway and Barclay, 2001)

  • Sexual Dimorphism
  • female larger
  • Range mass
    4.7 to 7.0 g
    0.17 to 0.25 oz
  • Average mass
    5.88 g
    0.21 oz
  • Range length
    81.0 to 93.0 mm
    3.19 to 3.66 in
  • Average length
    87.33 mm
    3.44 in
  • Range wingspan
    205 to 245 mm
    8.07 to 9.65 in


Western small-footed bats are polygynandrous, and reproduce seasonally. Western small-footed bats generally begin their reproduction in early July, but some members have been noted to begin as early as March in the southern part of their range. Mating season begins when the males' reproductive glands enlarge. These bats mate prior to hibernation and females store sperm until the spring. During the mating season male western small-footed bats will enter daily torpor to conserve energy.

Reproductively-active (sperm-storing) females emerge from hibernation earlier in the year than males. The litter size of western small-footed bats is almost always 1 young, but twins have been reported once. Lactating females can be found as early as March and as late as June, indicating they are nursing their young. Post-lactating females have been captured in late July. (Holloway and Barclay, 2001)

These bats breed once yearly, ranging from March to August in southern parts of the range in the the fall or winter months in Canada (even during hibernation). Most female bats including western small-footed bats store sperm for an extended period of time - from mating in the late summer or fall until they ovulate as they exit their hibernacula in the spring. Gestation time is 1-2 months; this timing is not exact due to sperm storage and delayed ovulation post-mating. In Canada, young are born in June or July.

One offspring is produced per mating couple, per mating season. The offspring of western small-footed bats on average have a birth mass of 1.1 to 1.6 grams. Most western small-footed bats will roost alone even while pregnant and when they do roost with other members of their species while pregnant, they split by sex. Maternity colonies can be as great as 16 adult females and pups.

Pups are weaned and volant in 4-6 weeks (average 5 weeks) and sexual maturity typically is reached just over a year post-birth. Juveniles do not breed in their first fall/winter. (Birkhead and Møller, 1993; Clarke, et al., 1996; Grindal, et al., 1992; Holloway and Barclay, 2001; "Status of the western small-footed bat (Myotis ciliolabrum) in Alberta", 2008)

  • Breeding interval
    Once yearly
  • Breeding season
    March - August in southern areas, late fall to winter in Canada
  • Range number of offspring
    1 to 2
  • Average number of offspring
  • Range gestation period
    1 to 2 months
  • Range time to independence
    4 to 6 weeks
  • Range age at sexual or reproductive maturity (female)
    1 to 1 years
  • Range age at sexual or reproductive maturity (male)
    1 to 1 years

Females give birth to one young and roosting in a small maternal colonies of 2-6 individuals. Sometimes they are solitary. However, colonies up to 19 have been recorded in California. Western small-footed bats are born in the late spring or early summer and will spend time with their mother having food provided to them until they can fly and hunt on their own. Males provide no parental care beyond the act of mating. (Holloway and Barclay, 2001; Ramsey, 1995)

  • Parental Investment
  • precocial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


Very little research has been conducted on western small-footed bat lifespan. Some research suggests an average lifespan of 12 years. However, this research is based on little data. These bats are not kept in captivity. ("Status of the western small-footed bat (Myotis ciliolabrum) in Alberta", 2008)

  • Typical lifespan
    Status: wild
    12 (high) years


Western small-footed bats tend to be more solitary than most bats. They do not appear to have a preference to roosting solitary or in small groups upwards of 19 members. These large groups are uncommon. Even in maternity colonies, groups of 2-6 females are typical. Maternity roost temperatures have been reported as 26-29 degrees C.

Activity times vary by publication. Some report that these bats are very predictable in their foraging behavior noted as leaving their roost to begin foraging always within about 25 minutes of sunset. Other report suggest they begin foraging later than other species. They feed opportunistically, but can occasionally be a beetle specialist when foraging in the same areas as California myotis (Myotis californicus). The latter species would become a moth specialist when they co-occur.

During a period of three months, western small-footed bats were recorded using 43 roost sites. This means that these bats change roost sites frequently. However, they do not travel great distances, even when emigrating as subadults. Males have been recording as dispersing just 70-134km from their natal range, a low number compared to sympatric species.

Western small-footed bats also enter a daily torpor during the summer months to conserve energy. These bats hibernate in caves and mines in small numbers, no more than 6 individuals per cave. They can even hibernate outside of caves, in narrow slits of rocky crevices. They hibernate singly in small cracks and crevices, and do awake infrequently during the winter to drink water. Rate of winter arousal has not yet been quantified. Temperatures of hibernation range from -3 to 9 degrees C. (Holloway and Barclay, 2001; Ramsey, 1995; Rodhouse and Hyde, 2014; "Status of the western small-footed bat (Myotis ciliolabrum) in Alberta", 2008)

Home Range

The home range of western small-footed bats is roughly an area of a kilometer in diameter. During foraging hours when most western small-footed bats are active it has been noted that no western small-footed bats will be seen further than a kilometer from their roost or hunting grounds. An exact measurement on territory size is not known, they tend to live in small crevices in cliff faces which change frequently throughout the day. (Downey, 2004; Holloway and Barclay, 2001; Ramsey, 1995)

Communication and Perception

Western small-footed bats communicate and perceive the world primarily through vision during daylight hours and echolocation nocturnally. These small-footed bats produce a call with a mean frequency of 46.87 ± 3.14kHz, a maximum frequency of 61.10k ± 10.28Hz, and a minimum frequency of 39.20 ± 2.11kHz. Male western small-footed bats have a call duration of 4.02 ± 0.89ms, while females have a call duration of 3.99 ± 0.63ms. However, these readings vary greatly across the geographic range. For example, frequencies can range from 40-60 kHz and call duration can be as little as 1ms and as great as 5ms in different areas.

When compared morphologically to similar bat species such as California myotis (Myotis californicus), pinnae (the external portion of the ear) height matters. Larger pinna equate to a lower average call frequency.

Like other bats, western small-footed bats can see during daylight hours. They may communicate in communal roosts with auditory calls, touch, and smell. (Decarvalho and O'Farrell, 2001; Holloway and Barclay, 2001)

Food Habits

Western small-footed bats are insectivores, with diets ranging from small flying insects found in their flight path, to large beetles found on the ground. The main staples of their diet include moths (Lepidoptera), true flies (Diptera), true bugs (Hemiptera), beetles (Coleoptera), and caddisflies (Trichoptera).

Feeding times vary by publication. Some report that these bats are very predictable in their foraging behavior noted as leaving their roost to begin foraging always within about 25 minutes of sunset. Other report suggest they begin foraging later than other species. They feed opportunistically, but can occasionally be a beetle specialist when foraging in the same areas as California myotis (Myotis californicus). The latter species becomes a moth specialist where they co-occur. (Downey, 2004; Holloway and Barclay, 2001; Ramsey, 1995; "Status of the western small-footed bat (Myotis ciliolabrum) in Alberta", 2008; Swier, 2003)

  • Animal Foods
  • insects


Western small-footed bats, much like many other species of bat suffer heavy predation from species of birds. Birds of prey make up the majority of their avian predation. There are records of other types of birds such as Mexican jays (Aphelocoma wollweberi) and blue jays (Cyanocitta cristata) preying opportunistically on western small-footed bats. ("Bats in the south coast ecoregion: Status, conservation issues, and research needs", 2005; McCune, 2016)

Ecosystem Roles

Western small-footed bats likely have little impact on their environment. Very little predator/prey information exist on western small-footed bats. Some birds prey on western small-footed bats and that western small-footed bats are generalized insectivores.

Several parasites species use western small-footed bats as a host species. These species are typically mites and bat bugs. The species that prey on western small-footed bats include protozoan coccidia (Eimeria pilarensis and Eimeria rioarribaensis), nematodes (Longibuca lasiuria), mites (Macronyssus cosbyi, Spinturnix carloshoffmani, Trombicula myotis, Leptotrombidium myotis, Leptotrombidium myotis and those in the family Macronyssidae), and bat bugs (Cimex pilosellus). (Holloway and Barclay, 2001; McCune, 2016; Ritzi, et al., 2002)

Commensal/Parasitic Species
  • Coccidia Eimeria pilarensis
  • Coccidia Eimeria rioarribaensis
  • Nematode Longibuca lasiuria
  • Mite Macronyssus cosbyi
  • Mite Spinturnix americanus
  • Mite Spinturnix carloshoffmani
  • Mite Trombicula myotis
  • Mite Leptotrombidium myotis
  • Bat bug Cimex pilosellus
  • Mite in family Macronyssidae

Economic Importance for Humans: Positive

Western small-footed bats are not known to have a positive economic impact on humans. (Holloway and Barclay, 2001)

Economic Importance for Humans: Negative

There are no known adverse effects of western small-footed bats on humans.

Conservation Status

Western small-footed bats in the United States were federally considered a category 2 candidate species, but this category no longer exists in the US Fish and Wildlife ratings system. Prior to 2018, it meant that the species could be warranted for listing but data were lacking to support a credible proposal. Several states and agencies have them listed as species of concern. For example, Montana lists them as an "S4" species, meaning that they may be stable but declines have been suggested. In British Columbia, they are a “blue list species” meaning that they are a risk-vulnerable species. The IUCN Red List lists them as a species of "Least Concern." These bats have no special status on the U.S. federal list of endangered species, CITES, or the State of Michigan List.

Threats vary by region. In southern California, urban expansion has been a threat to their populations. Texas suggests that the closure and sealing of abandoned mines might affect these bats, and that they could be indirectly impacted by pesticides. In Canada, indirect effects of dams (loss of flooding to the streamside forests in which they forage) are listed at the most substantial threat. Threats to boulderfields and cliff faces would also have a negative impact on western small-footed bats. Continuing wind turbine development may be a threat in coming years.

Currently the main conservation effort towards western small-footed bats is happenstance. Many of the regions in which they naturally inhabit are government-protected lands such as Dinosaur Provincial Park in Canada. Conservation plans do exist and research on roosting behavior to benefit conservation efforts is being studied. Washington state is currently working on a conservation plan to study bats in the region including western small-footed bats and develop a functioning conservation effort with government agencies and landowners to reintroduce roost and foraging sites for the bats. This plan also introduces ideas on how to minimize potential harm to the bats and their prey. This includes minimizing the amount of contaminants put into the environment and identifying locations needing an immediate clean-up. (Arroyo-Cabrales and Álvarez-Castañeda, 2017; "Bats in the south coast ecoregion: Status, conservation issues, and research needs", 2005; Findlay, 2017; Hayes and Wiles, 2013; "Status of the western small-footed bat (Myotis ciliolabrum) in Alberta", 2008; "Western Small-footed myotis (Myotis ciliolabrum)", 2018; "Western small-footed myotis (Myotis ciliolabrum) predicted suitable habitat models created on October 11, 2017", 2017)

Other Comments

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 ciliolabrum mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America.


David Thomas (author), Radford University, Layne DiBuono (editor), Radford University, Lindsey Lee (editor), Radford University, Kioshi Lettsome (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



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

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


uses smells or other chemicals to communicate

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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.


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.

female parental care

parental care is carried out by females


union of egg and spermatozoan


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).


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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


active during the night


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


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


remains in the same area


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


associates with others of its species; forms social groups.


lives alone


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).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


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.

young precocial

young are relatively well-developed when born


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