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Myotis evotiswestern long-eared myotis

By Christopher Weber

Geographic Range

The geographic range of Myotis evotis, or long-eared Myotis, includes much of the western United States from the Pacific Coast to the front range of the Rocky Mountains and western Dakotas. The geographic range reaches up into the lower Canadian provinces of British Columbia, Saskatchewan and Alberta and south into central New Mexico and Arizona. Although widespread, M. evotis is not particularly common throughout the majority of its range. (Manning and Jones, 1989; Manning, 1993)

Two subspecies exist: M. e. evotis of the mountains and high plains of the western U.S. and soutwestern Canada, and M. e. pacificus of coastal regions of the Pacific Northwest. (Manning and Jones, 1989; Manning, 1993)

Habitat

Myotis evotis is found in a wide range of habitats, but is most commonly found in mixed coniferous forests, from humid coastal areas to montane forests. Elevation ranges from sea level on the Pacific Coast to 2,830 meters in the mountains of Wyoming. The habitat of M. evotis is largely dependent on what the bats use for their day roosts. In southern British Columbia, long-eared myotis roost in tree cavities in dense forests. In adapting to forest management in certain areas of British Columbia, they have recently been found to roost in the stumps of clear-cut stands. Long-eared myotis prefer the stumps of ponderosa pine and lodgepole pine in these areas. In the large uninterrupted forests of the Pacific Northwest, M. evotis uses large snags for day roosts. These bats usually prefer snags that reach high into or above the forest canopy. In the badlands of the South Sasketchawan River Valley in Alberta, M. evotis are mostly found roosting in the crevices of sandstone boulders. Other places which function as day roosts are abandoned buildings, cracks in the ground, caves, mines, and loose bark on living and dead trees. (Chruszcz and Barclay, 2002; Chruszcz and Barclay, 2003; Manning and Jones, 1989; Nagorsen and Brigham, 1993; Vonhof and Barclay, 1996; Vonhof and Barclay, 1997; Waldien, et al., 2000)

  • Range elevation
    0 to 2,830 m
    0.00 to ft

Physical Description

Myotis evotis is dull to pale brown or straw colored with black ears and membranes. The ears, ranging between 19 and 22 mm in length, are the longest of any North American Myotis. The tragus is long and slender. The calcar has little to no keel. The auditory bullae are relatively large compared to other Myotis bats. The dentition is 2/3, 1/1, 3/3, 3/3. Total length, observed in a population of South Dakota bats, ranges from 87 to 100 mm.

Myotis evotis exhibits very little sexual dimorphism, with females being a bit larger than males, though only showing slight differences of length in ear and fifth metatarsal.

There is evidence of geographic variation in size. Specimens of M. evotis from British Columbia have larger skulls than those from Washington; Washington bats are more similar to those found further inland.

Myotis evotis morphologically overlaps with Myotis keenii. The two are sympatric in coastal areas of British Columbia and Washington. The geographic variation of M. evotis has made it difficult to distinguish between the two, and in some collections, identification errors have been made. No external features have been identified that clearly seperate the two species. The skull of M. evotis contains a longer tooth row than that of M. keenii. The distance from the last upper pre-molar to the last upper molar is greater than 4.2 mm. Another Myotis species that is difficult to distiguish is Myotis septentrionalis, commonly known as northern long-eared myotis. Longer tooth row and longer ears help distinguish M. evotis. (Manning and Jones, 1989; Nagorsen and Brigham, 1993; Van Zyll De Jong and Nagorsen, 1994)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • Range mass
    5 to 8 g
    0.18 to 0.28 oz
  • Range length
    87 to 100 mm
    3.43 to 3.94 in
  • Average wingspan
    250 mm
    9.84 in

Reproduction

Mating systems for M. evotis are relatively unkown. Although some similarities to other Myotis species can be inferred, actual data for M. evotis do not exist.

Most species of the genus for which there are data appear to be polygynandrous. Myotis myotis mating involves the females from different colonies traveling several miles to male roost sites. Little is observed in male behavior in attracting females. Reproduction in Myotis lucifugus involves copulation and insemination prior to hibernation. The sperm are then stored in the uterus until spring. (Vaughn, et al., 2000; Zahn and Dippel, 1997)

Records of M. evotis reproduction are very incomplete. Most data are either based upon anecdotal accounts or museum specimens. The young are born in late spring/early summer. Lactating females have been collected in July and August. Myotis evotis reproduces once per year, and females may form maternity colonies of 5 to 30 individuals in the summer (colonies may contain a few males), or they can remain solitary.

The young are born naked with sharp milk teeth. Size of the neonates ranges around 7 to 8 cm, with a weight of around 1 to 1.5 grams. (Manning and Jones, 1989; Manning, 1993; Nagorsen and Brigham, 1993)

A study of reproducing females in Alberta produced some interesting data on roost differences between pregnant and lactating females. Pregnant females roost in horizontal rock crevices, which are closer to the surface, warm rapidly, and have a higher mean daytime temperature. Pregnant females can maintain a higher body temperature at a lower cost to them by roosting in a warmer place. The horizontal surface rock crevices cool very quickly, however the bats spend these cool hours foraging. When they return to the cold roost, they drop into torpor until passively warmed by the ambient temperature, thus saving more energy for use towards fetal development.

Females who had given birth to young used deeper vertical rock crevices, which maintain a higher overall temperature. Juveniles that are left in the roost while the mother forages can not effectively maintain their high body temperatures. Vertical rock crevices fluctuate less in temperature, keeping the juveniles warmer and more stable. (Chruszcz and Barclay, 2002)

  • Breeding interval
    Myotis evotis breeds once per year.
  • Breeding season
    Mating occurs in autumn or early winter.
  • Range number of offspring
    1 to 1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    40 to 60 days

Parental investment is not well known for M. evotis. Lactating females choose a roost that is suitable for the young, which can not yet thermoregulate. Maternity roosts are often made up of several to several dozen individuals. The roost differs from that chosen while pregnant. Length of lactation and parental care has not been reported. The role of males in parental care has not been reported, but, as in most bats, it is likely that parental care is provided solely by the female, who nurses, protects, and grooms the altricial offspring. (Manning and Jones, 1989; Waldien, et al., 2000)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female

Lifespan/Longevity

The lifespan of these animals has been reported as a maximum of 22 years in the wild. It is unlikely that most individuals live that long.

Behavior

Myotis evotis is either solitary or roosts in colonies of up to 30 individuals. Both sexes use a variety of roost sites. In the Pacific Northwest, the variety of female roost sites exceeds that of any other bats in that area. In forest populations, these bats usually roost in large snags in canopy gaps, or else in stumps in clear-cut areas. They will roost in stumps instead of competing with other species for the relatively small remaining number of large conifer snags. Snags in canopy gaps and stumps receive more sunlight, thus maintaining a higher ambient temperature. Myotis evotis are hypothesized to lower their thermoregulatory costs by using the sun to passively warm their bodies after a state of torpor. The re-warming is the most energy-demanding phase of torpor for bats.

Myotis evotis was observed to be active at lower temperatures than other bats in the same region. The species forages later in the evening and for longer periods than others. These bats are thought to migrate short distances between summer and winter ranges, although winter ranges for long-eared myotis are unreported. (Manning and Jones, 1989; Vonhof and Barclay, 1996; Waldien, et al., 2000)

Solitary behavior leads to added hardship due to the inability to take advantage of heat accumulation in roosting groups, or maternity colonies. Torpor results in slowed embryonic development, prolonged gestation, and reduced milk production in reproducing females. This delayed parturition or weaning of young is quite detrimental to a temperate zone bat, because the feeding season is already truncated. Unique feeding behaviors have ameliorated these problems for M. evotis. However, at the edge of their range these bats exist on a very tight energy budget. (Chruszcz and Barclay, 2002)

Home Range

The size of M. evotis home ranges has not been reported.

Communication and Perception

Echolocation is essential to M. evotis, as it is through this means that these bats are able to capture their prey. Echolocation can be used in different ways when capturing prey. Changing calls or ceasing calls are both options for capturing prey in different situations. Although echolocation is the main means of capturing prey when “hawking” insects from the air, M. evotis will cease calling and use prey-generated sounds to guide the attack. This ability has many ramifications in feeding behavior, habitat range, and prey selection for M. evotis. Tympanate moths are a primary food source, and these foraging tactics make M. evotis all the more effective at capturing prey in the air or off a surface. (Faure and Barclay, 1992)

Other forms of communication or uses for echolocation for M. evotis are not completely known. Other echolocating bats have been found to actually use echolocation as a means of communication with each other. Myotis lucifugus was observed to use echolocation in identifying roosts, mating sites, hibernation sites and feeding areas. Other bats have been found to react aggressively to echolocation calls of conspecifics thus maintaining spacing between individuals. Echolocation can also facilitate mother-young recognition. (Vaughn, et al., 2000)

Although reports in the literature are absent, we may infer that mothers and their young use some tactile communication. It is also likely that this type of communication occurs between mates. Chemical communication has not been reported for these animals.

Food Habits

Myotis evotis is insectivorous. These bats emerge to feed approximately one hour after dark. They prey mainly on moths, but their diet also includes beetles, flies, and spiders. They can take prey from the air (hawk) as well as from surfaces (glean). The ability to incorporate both methods of foraging requires a pattern of flight that is slow and methodical, and which requires more energy compared to the flight patterns of faster-flying bats. Because the methodical flight requires more energy, these bats are forced to forage for prolonged periods. The dual method of foraging also allows for foraging and reproducing in less hospitable climates, due to the access to more than one source of prey. Females can breed in high cool climates, where there is decreased availability of flying insects. Myotis evotis can forage for longer periods because it does not rely on a precise heightened insect activity period. Aerially foraging bats focus on peak times of insect abundance, dusk and dawn. Myotis evotis can forage throughout the night, and not rely on peak foraging windows.

Myotis evotis studied in a montane grassland area was found to feed on the following insect families: Lepidoptera, Coleoptera, Diptera, Neuroptera, Hymenoptera, Hemiptera and Homoptera. Considered temporal opportunists, M. evotis certainly feed to a large extent on moths. Moths are both gleaned from surfaces or taken in the air and both techniques require a unique method of echolocation. Myotis evotis adjusts its echolocation method to fit the acoustical limitation of each foraging situation. For example, when gleaning insects off a surface, the bat has to deal with interference clutter (surfaces reflecting off with more energy than the prey located on that surface). Myotis evotis uses lower amplitude calls when gleaning, and stops calls just before striking, when it actually uses sounds made by the prey to help coordinate its attack. While taking insects from the air, M. evotis uses techniques such as a feeding buzz, used to constantly monitor the environment, even when enacting the final attack on a prey. (Chruszcz and Barclay, 2003; Faure and Barclay, 1992; Faure and Barclay, 1994; Manning and Jones, 1989)

Although once considered an active prey specialist, M.evotis is actually a passive prey specialist. The selectivity for moths in the diet of this species is due to a biased sensory system that has especially acute ability to perceive prey-generated sounds. The short duration, broad-band, frequency modulated echolocation calls used by M. evotis are certainly useful for the gleaning of prey off surfaces; however, evidence indicates that they can glean insects from surfaces without use of echolocation. Myotis evotis has extremely sensitive low frequency hearing and can use prey-generated sounds to detect prey without the use of echolocation. This was revealed by an experiment with a hidden moth where echolocation could not confirm the location of prey, yet the bat was still accurate in attacking. The advantages of gleaners using a variety of sensory cues are many. Because tympanate moths have evolved a sensitivity to and avoidance of echolocation calls, M. evotis, which can locate these moths without use of echolocation calls, are more likely to take such moths than are less adept species of bats. (Faure and Barclay, 1992; Faure and Barclay, 1994; Faure, et al., 1990)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods

Predation

In populations of M. evotis living in a Pacific Northwest forest of clear-cut stumps, possible predators include chipmunks (Eutamias amoenus) and bears (Ursus americanus), in addition to other common small mammal predators. To avoid these predators, M. evotis switches roosts frequently. Switching roosts limits the amount of scent that can build up from constant use. In tree bark roosts, the bats often were found face-up at the bottom of the cavity and were well camouflaged. (Vonhof and Barclay, 1996)

In British Columbia, a yellow-bellied racer, Coluber mormon, was established as a predator. (Manning and Jones, 1989)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

As with all small mammals, the amount of energy M. evotis requires to maintain metabolic function results in considerable impact on ecosystems. With M. evotis needing more energy than most, due to its unique energy-intensive flying patterns, it forages for a longer time and is perhaps more successful at taking prey. Wide distribution is testament to the relative success of M. evotis . This species clearly has a large impact on populations of insects upon which it preys. (Manning, 1993; Vaughn, et al., 2000)

Economic Importance for Humans: Positive

As an insectivore, M. evotis has some effect on insect pest control.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

M. evotis is a known carrier of rabies. (Manning and Jones, 1989)

Conservation Status

Myotis evotis is a previous candidate 2 species under the U.S. Endangered Species Act. It has no formal federal status, but is recognized as state sensitive in many areas of the western U.S.

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 evotis 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)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Christopher Weber (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

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

acoustic

uses sound to communicate

altricial

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.

arboreal

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.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

echolocation

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.

endothermic

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.

fertilization

union of egg and spermatozoan

forest

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

hibernation

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.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

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).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

mountains

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.

nocturnal

active during the night

polygynandrous

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

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

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

social

associates with others of its species; forms social groups.

solitary

lives alone

sperm-storing

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.

tactile

uses touch to communicate

temperate

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).

terrestrial

Living on the ground.

ultrasound

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

visual

uses sight to communicate

viviparous

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

References

Chruszcz, B., R. Barclay. 2002. Thermoregulatory ecology of a solitary bat, Myotis evotis, roosting in rock crevices. Functional Ecology, 16: 18-26.

Chruszcz, B., M. Barclay. 2003. Prolonged foraging bouts of a solitary gleaning/hawking bat, Myotis evotis . Canadian Journal of Zoology, 81: 823-826.

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 http://www.fort.usgs.gov/WNS/.

Faure, P., R. Barclay. 1994. Substrate-gleaning versus aerial-hawking- Plasitcity in the foraging and echolocation behavior of the long-eared bat, Myotis evotis . Journal of Comparative Physiology, 174/5: 651-660.

Faure, P., R. Barclay. 1992. The sensory basis of prey detection by the long-eared bat, Myotis evotis, and the consequences for prey selection. Animal Behavior, 44/1: 31-39.

Faure, P., J. Fullard, R. Barclay. 1990. The response of tympanate moths to the echolocation calls of a substrate gleaning bat, Myotis evotis . Journal of Comparative Physiology, 166/6: 843-849.

Manning, R. 1993. Systematics and evolutionary relationships fo the long-eared myotis, Mytois evotis (Chiroptera: vespertilionidae). The Museum, 37: 1-58.

Manning, R., J. Jones. 1989. Myotis evotis. Mammalian Species, 329: 1-5. Accessed March 25, 2004 at http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/..

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

National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at http://www.nature.nps.gov/biology/wildlifehealth/White_Nose_Syndrome.cfm.

Van Zyll De Jong, C., D. Nagorsen. 1994. A review of the distribution and taxonomy of Myotis keenii and Myotis evotis in British Columbia and the adjacent United States. Canadian Journal of Zoology, 72/6: 1069-1078.

Vaughn, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, Fourth Edition. United States: Thompson Learning, Inc..

Vonhof, M., R. Barclay. 1996. Roost-site selection and roosting ecology of forest-dwelling bats in southern British Columbia. Canadian Journal of Zoology, 74: 1797-1805.

Vonhof, M., R. Barclay. 1997. Use of tree stumps as roosts by the western long-eared bat. Journal of Wildlife Management, 61/3: 974-684.

Waldien, D., J. Hayes, E. Arnett. 2000. Day-roosts of female long-eared Myotis in Western Oregon. Journal of Wildlife Management, 64/3: 785-796.

Zahn, A., B. Dippel. 1997. Male roosting habits and mating behaviour of Myotis myotis . Journal of Zoology, 243: 659-674.

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