ORDER CHIROPTERA   

                                                                         
ARTICLES

Chiroptera is Latin for "hand-winged”.  As a result of their specialized forelimbs, bats are the only mammals that truly fly. The bat is highly modified for flight. Like birds, its bones are hollow, with large chest muscles.  Unlike birds, which flap their wings up and down, bats "swim" through the air, rotating their wings to catch the air with the membrane.  All bats in our region are nocturnal and insectivorous. Some species are solitary; others are colonial (gregarious). 

Although there are differing opinions regarding the visual abilities of bats, bats utilize "echolocation" to avoid obstacles and to find food in total darkness.  Near the roosting nest, a different "honking" sound is made to warn other bats of their presence in order to avoid collisions.  The range of frequency employed by bats is between 25 and 115 kHz, while the human ear can rarely hear up to 20 kHz.  In normal flight, a big brown bat may emit 10 pulses per second, with an increase in pulses as needed.  Pulses may reach 200 per second during pursuit of prey.  Various moths have developed the ability to hear the bat’s echolocation and produce evasive flight maneuvers.  Furthermore, some moths have evolved a series of grooves on their thorax that they can scrape together to produce ultrasound, jamming the bat’s navigational system with noise.  In response, some bats have switched to higher frequencies that moths can’t produce.  In cases of bats capturing prey on the ground or on vegetation, bats can emit sounds too low for the prey to hear.  Such use of low-intensity sounds enables a bat to “whisper”.

Bats actually echolocate using three different systems, depending on the species of bat.  One system, used by bats found in Europe, Asia, and Australia, is known as constant frequency, or CF. This system utilizes brief, intermittent sound bursts at a given frequency, normally around 115 kHz.  A second system, used by many North American bats, is known as frequency modulation, or FM.  This method of echolocation emits bursts of sound that sweep through a wide range of frequencies (from 50 kHz to 100 kHz) in two thousandth of a second.  This sound FM signal is the equivalent to radio FM signals.  The third system is a combination of CF and FM, used by some other North American bats.  In these species, the long-range CF sounds are used first to locate the object, followed by FM sweeps that give it a much more detailed idea of the object.

There are six main annual events in the lives of most bats; hibernation, a short spring "swarming" or "staging" period upon emergence from hibernation, spring migration, the summer birthing period, fall migration and fall swarming prior to hibernation.  Bats mate in the fall, before hibernation, or migration, but the egg is not fertilized until the following spring. This habit of carrying the sperm over the winter is called delayed fertilization. Bats have the longest period of sperm storage of any mammal. This allows embryo development to begin very soon after the females emerge from hibernation.  Some mating occurs in winter and the following spring, assuring all females can become impregnated.   All species of North American bats bear their young in a two to five week period in late spring to early summer.  Most bats produce their first young at the age of one year.  Being animals of flight, including during pregnancy, most North American bats have only one young per litter.  The exception are the three migratory forest-dwelling bats, who, apparently, due to larger loss of young in exposed tree sites, have more young and, correspondingly, more mammae.

All bats of the eastern US are capable of hibernation in winter, and they will also reduce metabolism and enter torpor during cool days, as an energy-saving mechanism.  Studies have shown that bat body temperature drops to conform with the temperature of the cave, while the heart rate slows from 600 beats per minute to 10 to 80 beats per minute.  Brown bats store energy as brown fat.  About 75% of the stored fat is used during the wakeup periods, with the other half-gram serving to maintain the bats life functions through the entire winter of hibernation.  Many studies of big brown bats in hibernation have been conducted.  While normal awake body temperatures are 99 degrees, apparently the body temperatures match the environment down to a temperature of 30 degrees while breathing can drop from 200 times a minute to once every four to eight minutes. As all true hibernators, bats will occasionally awaken during winter to prevent muscle atrophy and defecate, and may even change caves. However, studies show bats can last without arousal for two to three months during deep hibernation.   Arousal from hibernation to a metabolic state supporting sustained flight can occur in as little as seven minutes.  Heat is generated in several ways.  The heart rate increases greatly and rises as high as 700 to 800 beats per minute.  Brown fat is burned and shivering is also conducted by some species. 

Most bats hibernate relatively near their summer range, but forest dwellers, like the red, silver-haired and hoary bats, migrate to southern winter ranges, where they may, or may not , hibernate. (Even among these forest dwelling species, some remain in the summer range to hibernate.)  Some species overwinter in large hibernating colonies (which can make the species more susceptible to human impact), others overwinter in small groups, or singularly. Most overwintering colonies break up in the spring with females forming their own nursery groups giving birth to litters of usually one or two (species dependent – the woodland red and hoary bats are solitary and do not cluster).  Since female bats must continue flying while pregnant, litters are small, but are compensated by long life expectancies (up to 30 years).  Males may or may not form their own groups. In some species, summer ranges are separate for male and females. 

Roosts are either night roosts or day roosts.  Night roosts provide places to rest between feeding and may be important social-interaction sites.  Day roosts are of four types: nursery roosts (self-explanatory), summer male roosts (while females are at the nursery roosts), transient roosts (used in spring and fall in migration---possibly major sites of copulation), and winter roosts (where they hibernate).

Some bats (Indiana bats) require limestone caves, others hollow trees or loose bark. Some, like the small eastern pipestrelle, are "heavy sleepers", while others, like the Townsend’s big-eared bat, are easily aroused. The red bat is the most sexually dimorphic bat (sexes exhibit different colors). 

Despite general belief, bats do not prey heavily on mosquitoes, owing to the small size of the mosquitoes and the habit of mosquitoes to fly close to the ground.  In fact, stomach contents in most studies show mosquitoes making 3% or less of their diet.  The two big-eared species (Townsend’s and Rafinesque’s) feed almost exclusively on moths.

Despite public opinion, far less than 1 % of all bats contract rabies nor do they act as symptomless carriers.  Unlike the typical rabies of most mammals, bat rabies is a different disease, which produces "dumb" symptoms, with the bat just lying there, rather than the ferocious aggressive symptoms of the common "furious" form of rabies. 

As a result of their communal denning (and absence of communal grooming), there are close to 700 species of insects that live exclusively on the bodies of bats. 

The mammae of bats are located on the side of the mother; not in front, like every other mammal.  

Most authorities believe bats and gliding lemurs evolved from insectivorous, probably arboreal, ancestors.  Bats evolved approximately 55 million years ago, early in the Eocene period. 

Worldwide, bats constitute the second largest order of mammals, behind only rodents.  There are approximately 18 families, 192 genera and 977 species of bats known today (according to Nowaks Walker's Mammals of the World).  

According to the Checklist of North American Mammals (Jones), 45 species of bats in four families and 19 genera are found in the North America.  

Thirteen species are found in the Appalachian region, all of the Vespertilionidae family.  Of these, the federally listed endangered gray bat is known from summer colonies in only two SW Virginia counties and will not have a species account in this Appalachian region website.

BACK TO THE TOP OF CHIROPTERA

Family Vespertilionidae - Plainnose Bats

These "evening" bats constitute the largest family of bats, including 43 genera and 342 species (Nowak).  All of the bats in the Appalachian region are in this family.  Bats in this family have simple, unmodified muzzles. The tail does not extend noticeably beyond the "interfemoral" membrane.   Some members of this family are solitary, others roost in pairs or in small groups, and still others generally shelter in colonies.  The colonial species normally return to the same roosting site each year.  Some species remain colonial year round while others only gather together for winter hibernation.  Because these bats are insectivores, they must either migrate (the 3 tree-dwelling species) or hibernate (the 9 cave-dwelling species) in winter.    Females separate from males in summer to form nursery colonies, either singly or in large colonies.  For bats that hibernate, breeding occurs in the fall and often again in the spring; the two breeding periods resulting in a single litter, with delayed fertilization of the fall mating enabling the sperm to be stored overwinter with ovulation and fertilization occurring in the spring.  Most bats have only one young per year.  This low reproductive rate is offset by the fact that bats live longer than most mammals of their size.   The red bat and hoary bat belong to the only genus of bats that commonly have more than two young per birth.  It is hypothesized that this high fecudity is a adaptation to high mortality resulting from roosting in trees and being exposed to predation.   

They all have excellent echolocation abilities, and have the ability to exercise delayed fertilization.  Many have been shown to have excellent homing capabilities.

The big brown bat is one of the most common and widely distributed of our bats.  It is known to "vibrate" when resting and content.  Similar vibrations have been found in several other North American species, and can be likened to the "purring" of cats.

The Myotis genus (little brown bats) has the widest distribution of any genus of bats.  There are 87 species in this genus (Nowak).

Of 342 species worldwide, 12 species are found in the Appalachian study area (Jones).

NORTHERN MYOTIS (Myotis septentrionalis) (mouse, ear; unknown, probably refers to northern distribution)   

Appalachian Region Distribution: Throughout.
Continental Range: Eastern US.  No subspecies described.
Abundance: Uncommon.  May be more common than thought due to their difficulty to locate.
Size and Molt: Head and body is 1.6 - 2.2"; 0.18 - 0.35 oz. 
Mammae: One pair
Habitat: Heavily forested areas. Summer roosts in hollow trees or under bark, sometimes using cooler caves at night; winter roosts in caves.   One Missouri study found these bats foraging primarily in hillside and ridge forests rather than in riparian and floodplain forests.
Active Period: Nocturnal. Hibernates from late October to late March near summer range.
Diet: Soft-bodied insects, especially moths, butterflies, and spiders.
Social Structure: Females form small nursing colonies (up to several dozen) in April/May; males are solitary. Hibernates in small groups, often only 2 or 3 together (although as many as 350 have been reported during winter in New England) under lose bark or shingles.  Sometimes winters with little brown bats and other species.  Often not seen in winter dens due to their tendency to seek out cracks and small crevices instead of ceilings and walls.  Known to swarm by the hundreds at cave entrances in the fall.
Life Cycle: One litter of one in June/July; later than most bats.  Mates in fall with delayed fertilization.  Gestation of about 40 days. Flies on its own in four weeks.  Matures in one to three years.  Life span up to 18 years.

Remarks: This bat has long been known as Keen’s bat, Myotis keenii septentrionalis, or, the eastern long-eared bat; a subspecies of one species that reaches from the Canadian Pacific coast to the eastern US.   However, a 1979 study concluded that the morphological differences between the population found in the Pacific northwest and the eastern form supported the species designation of M. septentrionalis.  However, some varying opinions on the species classification exists. In 1992, one study separated keenii and septentrionalis , while another supported keeping one as a subspecies of the other.  The 1997 Checklist of North American Mammals (Jones) maintains the western Pacific coast Keen's myotis separate from the northern myotis, which is found from the Canadian Rockies east, including most of the eastern US. In order to maintain consistency, this is the designation I will use.

BACK TO THE TOP OF CHIROPTERA

EASTERN SMALL-FOOTED MYOTIS (Myotis leibii) (mouse, ear; Dr. G.C. Leib)

Appalachian Region Distribution: Throughout.               
Continental Range: From the New England states and adjacent Canada, south along the Appalachian Mountains to northern Alabama and Georgia.    No subspecies described.
Abundance: Little is known about this bat. Appears to be uncommon in occurrence, but this could be in part the result of it’s inconspicuous roosting sites.  Is listed as threatened in PA.
Size and Molt: Smallest of the myotis genera; Head and body is 1.7 - 1.9"; 0.11 - 0.32 oz.
Mammae: One pair
Habitat: Mountainous areas (especially hemlock forests) near caves. Summers in buildings, hollow logs and rockpiles; winters in inconspicuous crevices in caves and under boulders.
Active Period: Nocturnal, but early in the evening. This bat hibernates only during the coldest months of the winter. They are the last to enter and first to leave the hibernaculum (mid-November to March).  Often found swarming at cave entrances. Will wake every two weeks and fly about outdoors on warm winter nights, but will not feed.
Diet: Feeds low in branches on flies, beetles, leafhoppers, true bugs, and flying ants.  Puts on about 2 ounces of brown fat in winter, of which nearly three quarters is used in the awake periods mentioned above.
Social Structure: Females separate shortly after hibernation to form nursing groups of 10 to 20 while males probably form small groups or are solitary. NAS states nursery colonies may number in the thousands (up to 6,700).  Mate in the late fall at the hibernaculum before entering hibernation.  A solitary hibernator, but will also be found in small groups or even rarely in larger groups up to 100.  Is known to migrate several hundred miles to a hibernating site.
Life Cycle: One litter of one born in June after delayed fertilization.  Normally mates in fall, but can mate in spring, with limited delayed in fertilization.  Gestation of about 40 days.  Can fly at three to four weeks old.  Life span of 12 years.
Nest: One of the few species that sometimes roosts on the ground.  Although most commonly found roosting in cave passageway walls or small crevices, they are known to nest under rocks on a hillside or in a quarry, in underground burrows and under talus on the floor of caves.

Remarks: This, and the eastern pipistrelle, are the smallest bats in eastern US.   First described by Audubon and Bachman.  

Formerly known as Myotis subulatus. 

BACK TO THE TOP OF CHIROPTERA

LITTLE BROWN MYOTIS (Myotis lucifugus) (mouse, ear; light, fleeing)

Appalachian Region Distribution: Throughout.                   
Continental Range: Most of North America.  No subspecies described.
Abundance: Locally abundant. (Perhaps the most common bat in the Appalachian region.) Population Density: Novak reports up to 25/square mile in favorable New England habitat. Size and Molt: Head and body is 1.8 - 2.1"; 0.25 - 0.35 oz. One molt.
Mammae: One pair
Habitat: Found anywhere. Forested areas; hollow trees, attics, or behind shutters in summer, caves in winter. Becoming more dependent on human structures for summer roosts.  Often roosts are near water.  Winters in cooler front rooms of caves rather than warmer deep rooms.
Active Period: Crepuscular to nocturnal. Will utilize “night roosts” for rests during the night before returning to the day roost.  By late October, hibernates in small clusters of 25 or 30 and in small numbers in caves and mines near the summer range.  In Canada, migrates several hundred miles south to hibernate (maximum recorded distance was 483 miles).  Awakes throughout the winter about every two weeks, using stored energy from brown fat. 
Diet: Mainly soft insects, such as flies, moths, mayflies, and other flying insects.  Known to feed by flying through swarms of small insects (often midges), rather than seeking individual insects.  They may fill up their stomachs within an hour and empty their digestive tracts two or more times a night (eating one third to one half their body weight per night).  Favorite feeding areas are often around lights or watercourses where insects can be easily found. 
Social Structure: Maternal nursing colonies of 50 to several hundred (up to 1,000) form in May, often in attics; males are solitary, or in small groups.  In fall, males and females congregate in roosts of several hundred, mating promiscuously before entering torpor.  Are known to winter in densities of up to 300,000.  Young may be carried by mother for first month, but commonly left hanging in nursing colony.
Life Cycle: One litter with one per litter. Mating in fall before hibernation (and often again in spring) with delayed fertilization until March. Gestation of 50/80 days allows for a June/July birth. For parturition (child birth), mother hangs by her thumbs (upside down for her) and catches neonates with hind legs and tail in the form of a basket as they’re born. Young flying in three weeks, with maturity at eight months. May mate in first fall, but normally not. Life span of 25 years (males longer than females).  A record of at least 34 years of age stands as the longest known bat longevity on record.
Nest: Three types of roosts are used by the little brown bat.  These are day and night roosts and the hibernacula.  Day roosts are more open areas, normally somewhat warmer than ambient temperatures when used as nursing areas, cooler for males and non-breeding females.  Night roosts are more confined spaces.  Hibernaculum are often nearby caves, but can be many miles away.

Remarks: The little brown myotis, whose nitrate-rich guano was sold as fertilizer in the first half of this century, is one of the most common bats in the US. 

 Develops layer of brown fat in fall to help supply energy for winter hibernation.  Has quite a range of heart rates, depending on season.  The highest rate recorded was 1,368 beats per minute and the lowest was 8 beats per minute (at 23 degrees).  Known to exhibit a marked homing tendency, or site attachment, and will return year after year to their natal roosts to bear their young.   

This bat can attain flight speeds of up to 35 km/hr and averages about 20km/hr.  They are known to migrate up to 275 km from their summer to their winter roosts.   The highest range of body temperature in any vertebrate occurs in this species, being cooled to 6.5 C without apparent harm and has also been found at 54 degrees.

BACK TO THE TOP OF CHIROPTERA

INDIANA or SOCIAL MYOTIS (Myotis sodalis) (mouse, ear; companion)  

FWS ENDANGERED SPECIES FILE

Appalachian Region Distribution: Throughout.
Continental Range: Eastern half of US, not in southern piedmont or coastal plain.  No subspecies described.
Abundance: Federally listed Endangered Species, due to limited wintering habitat and nature of forming massive colonies, making them more susceptible to human impact.
Habitat: Summers in small groups (30 to 80) under loose bark of dead trees, small caves or cavities; winters in great masses (500 to 1,000) on the walls and ceilings in large, cool and moist limestone caves.  These bats congregate in tightly-packed clusters (up to 300 per square foot) in caves with very narrow  temperature range (37 to 43 degrees) and a relatively high humidity (averaging 87%).
Size and Molt: Head and body is 1.8 - 2.0", 0.14 - 0.28 oz. One molt.
Mammae: One pair
Active Period: Nocturnal. Migrates as much as 300 miles in September and hibernates from October to late March. Throughout hibernation, bats arise every 8 to 10 days, and joins other awakened bats in the warmer area; get bored, and go back to the business of hibernating.
Diet: Prefers soft insects like flies, caddisflies and moths, but includes beetles and other insects near the tops of trees and aquatic invertebrates along riparian habitats.  Body fat increases by 50% prior to hibernation.
Home Range:  Within it's summer range, one nursery colony of 50 bats ranged about 1/2 mile along a riparian corridor in one night.  Banding studies have shown movements of these bats ranging up to 135 miles over  the course of a year.  Summer roosts are often near streams.
Social Structure: In summer, females form small nursing groups (occasionally up to 125) in hollow trees or under loose bark of dead trees; males sometimes form small groups in caves. Summer roosts often include one to three primary roosts of multiple dead trees (supporting 30 or more bats), and alternate roost sites, supporting fewer bats and roost trees.  Winter colonies can be 500 to 5,000, although Bat Cave, Carter Caves State Park, Kentucky, has a winter population of approximately 100,000.  Females leave the hibernacula shortly before males, in April to May.  May spread out over a 100 to 200 mile area, generally northwards.  Males tend to return to the hibernacula a few weeks prior to females; as early a late July, with both male and females peaking in September and October. .  
Life Cycle: One litter of one young. Mating occurs just before hibernation (at hibernaculum site), but delayed fertilization allows ovulation and fertilization soon after hibernation. Young born in June can fly in one month. It is not known if the newborn are mated in the first fall.  Life span up to 20 years. 

Remarks: Species name refers to tendency of the Indiana bat to hibernate in large numbers.  This makes them more susceptible to human disturbance than other species. Probably over 95% of the bats winter in 15 caves; six of them in Missouri, nine in the eastern United States.  Mammals of Virginia says 85%  of the known population – 400,000 in 1992; down from 500,000 estimated in 1973 - is found in two caves in Kentucky, two caves in Indiana, and in a cave and a mine in Missouri.  Fourteen of these hibernaculum have been listed as critical habitat for protection by EPA.  A large population inhabits Mammoth Cave National Park. As of a 1995 study, ten hibernacula caves were known in Virginia with about 2,500 bats.  In West Virginia, it is known from caves in Greenbrier, Hardy, Monroe, Pendleton, Pocahontas, Preston, Randolph, and Tucker counties.   They seem to be particularly affected by pesticides.  This, human disturbance, and flooding appears to account for the drastic decline in northeast US populations (71.5% decline over the past 15 years in Indiana, Illinois, and Kentucky alone). 

The Indiana myotis has a considerable homing ability.  Up to 67 percent of bats released 193 miles from the point of capture have returned successfully.  

BACK TO THE TOP OF CHIROPTERA

EASTERN RED BAT (Lasiurus borealis) (shaggy, tail; northern)

Appalachian Region Distribution: Throughout.
Continental Range: Most of North America; absent from the Rockies and the Great Basin.  This is the only subspecies in the eastern US. 
Abundance: The most common and widespread bat in the region.
Population Density: An Indiana study found a density of about one per acre.
Size and Molt: Head and body is 2.2 - 2.4"; 0.21 -0.49 oz. One of the few bats that is sexually dimorphic, the male redder and less frosted than females. The female is slightly larger than the male.
Mammae: Two pair, unlike most bats.  
Habitat: Strictly a tree dweller along riparian corridors.  Also is found in coniferous woods.   Summers roosts in dense trees, often hanging by one foot from a branch 4 to 10 feet above ground, near water. Spring may find mothers and young 10 to 20 feet above the ground. Winters in caves, hollow trees, and crevices.
Active Period: Nocturnal, foraging shortly after sunset (or even before sunset) over water, fields, and around street lights.  Are known for their extremely high feeding (300 to 600 feet) early in the evening, shortly after sunset.  They are known for being the first bat seen in the evening and are occasionally seen in broad daylight.   They are distinctive in routinely foraging in the late afternoon on warm winter days, when temperatures exceed about 50 degrees.  Extremely migratory, like the Hoary and Silver-haired bats, leaving during September and October for destinations as far south as Bermuda.  Apparently, males and females migrate at different times and have different winter and summer ranges.  Late fall and winter records from WV to Missouri are all of males.  Early spring records in Illinois include both sexes, and nearly all individuals found in Indiana, Illinois, Kansas, Louisiana and Missouri during the summer breeding season are females.  Locations of summer males are not known.  Some bats do not migrate, and have been recorded in winter with temperatures greater than 55 degrees.  During the winter, limited hibernation may take place, but the bats awake and forage on warmer days.
Diet: Includes both the hard and soft insects; moths, flies, crickets, beetles, bugs and the usual assorted flying insects.
Home Range: Tends to use the same area of about 100 yards (about 2 acres) night after night. Often found at the same street light for weeks during summer.
Social Structure: Very solitary in both summer and winter; even females rarely form nursing colonies. Although a few bats will not migrate, the majority migrate several hundred miles before reaching their winter range, where limited hibernation may occur with foraging on warmer days.  
Life Cycle: After females reach summer range, they have one litter of two to four (due to the second pair of mammae, not found in most species) in June after a 85 day gestation period from a August-October mating (earlier than most bat species –just before or during migration), although spring copulation has been observed. Copulation occurs in flight.  With two to four young, this bat produces young that are more altricial, requiring a longer period of parental care (note the two pair of nipples; not the one typical of other native bats).  Length of pregnancy is also much longer.  Young fly at three weeks and are weaned at six weeks.   Breeds in second or third fall.  Life span up to 12 years.

Remarks: Easily identified by its red coloration and graceful arching flight.  This is one of the few mammals in which the sexes are contrastingly colored.   The male is rusty-red, while the female is buff-chestnut; both with white frosted hair tips.   The mother carries the young so long that the mother is often found when it loses its hold on a branch from the weight and falls to the ground (W/H says that this has sometimes been thought to be true, but is not). Very cold and hot tolerant during torpor in the northern parts of their wintering range.  In fact, the red bat can withstand brief periods of below-freezing body temperatures without ill effects.  Red bats respond to subfreezing temperatures by raising the rate of respiration, assuming a spherical body shape, and stretching the furred tail membrane over the ventral body surface like a blanket.  This protects them from waking too frequently, and thus, wasting energy in the winter.  Members of the Lasiurus genus tend to be solitary and migratory, hanging individually among foliage.  Red bats are high and fast fliers, reaching heights of 600 feet and speeds of up to 40 miles per hour.  Also, the most colorful of bats. 

This is the only genus of bats that commonly have more than two young per birth.  It is hypothesized that this high fecudity is a adaptation to high mortality resulting from roosting in trees and being exposed to predation.   

There are 15 species in this hairy-tailed bat genus, including the next species.

BACK TO THE TOP OF CHIROPTERA

HOARY BAT (Lasiurus cinereus) (shaggy, tail; ash-colored)

Appalachian Region Distribution: Throughout.
Continental Range: Throughout continent.  There is only one subspecies in the eastern US.
Abundance: Uncommon.
Size and Molt:  Head and body is 3.2 - 3.5" ; 0.74 - 1.4 oz. This is the largest bat in eastern North America. Females are slightly larger than males. One molt.
Mammae: Two pair
Habitat: Solitary forest dwellers, often hanging from coniferous branches 10 to 15 feet above the ground in woods in the summer. Not normally found in caves.  Apparently, actually makes a nest of loosely attached leaves 10 - 17 feet off the ground, open at the bottom. Absent in winter.
Active Period: It is a strong flier, found well above the tree canopy and often late in the evening. It tends to be the last bat to appear in the evening, well after sundown, and then, often active all night.  Highly migratory (several hundred miles) and has not been recorded in Virginia or the Carolinas in summer. PA is southern limit to summer range, and probably the northern limit to the winter range. Some may migrate to Central Mexico, others may possibly stay in same area.  Migrates in September through November and again in March through May. See Social Structure for more detail.  
Diet: Prefers moths, also eats beetles, flies, dragonflies, grasshoppers, termites, wasps, and, due to its size, even smaller bats. Often feeds over water.
Social Structure: Solitary, or in small nursing colonies in summer, with females migrating in flocks of up to several hundred.  Both sexes share wintering grounds in southeastern US (southern Georgia and Alabama and northern Florida).  The sexes are separate during the summer range, with the males either remaining in the winter range or traveling to SW US, while the females are found from the Smokies and northwards along the Appalachians and lands to the north and west of these mountains.  (W/H says all males leave the winter range and travel to the western US).  On a national level, the summer population of northeastern US is mostly females, while the southwestern part of the continent is mostly males.  Two winter ranges are maintained; the deep southeast in the east, and southern California, south to Guatemala, in the west, where limited hibernation may occur with foraging on warmer days.  
Life Cycle: After reaching the summer range, females have one litter of two or three in June (litters of four and even two litters of five have been recorded - how that can occur with only four mammae is beyond me).  Nursery colonies are not formed; the hoary bat is a solitary bat.  Breeding occurs in the fall and winter months (delayed fertilization), with the females pregnant during the spring migration.  The hoary bat has a gestation period of about 90 days.  Young fly in four weeks, and breed in the second or third fall. Life span of 6 - 7 years, up to 12 - 14 years.

Remarks: This is the largest of the eastern bats.  As the name implies, this large bat has a beautiful, frosted coat. Notice similarities with the red bat of the same genus. This is the only genus of bats that commonly have more than two young per birth.  It is hypothesized that this high fecudity is a adaptation to high mortality resulting from roosting in trees and being exposed to predation.   

There are 15 species in this hairy-tailed bat genus, including the preceding red bat.  These two, plus the following are the only migratory bats in our Appalachian region. 

This is the only land mammal native to Hawaii.  

BACK TO THE TOP OF CHIROPTERA

SILVER-HAIRED BAT (Lasionycteris noctivagans) (hairy, bat; night, wandering)

Appalachian Region Distribution: Seasonally throughout.  See details in remarks below.
Continental Range: All continental US and southern Canada, reaching as far south as Bermuda and NE Mexico.  No subspecies described.
Abundance: Relatively uncommon.
Size and Molt: Head and body is 2.6 - 2.8"; 0.21 - 0.49 oz.
Mammae: One pair
Habitat: Mainly a tree-dweller in forested (especially coniferous) areas, usually along streams and rivers. Roosts in clumps of leaves, abandoned woodpecker holes, hollow trees, rock crevices and under loose bark.
Active Period: Normally seen an hour after sunset, usually over ponds and streams.  (Mammals of Virginia says they are early fliers, becoming active in late afternoon or early evening.)  Some stay put in fall, using the most secure of the summer roosts to hibernate in, but most migrate to southern states. Known to fly high.
Diet: Primarily beetles, but also caddis flies, stable flies, scarab beetles, moths and other sizable nocturnal insects.
Social Structure: A solitary, migratory, tree-roosting bat.  Females form small maternal groups (a dozen or less) in hollow trees in spring, but tend to be solitary the rest of the year, while males are solitary year-round.  It seems that male remain in the wintering range throughout the year, with females presumably only in the winter range in the fall and winter (see remarks below). Flies alone or in small groups, often over lakes, in relatively straight and lethargic manner.
Life Cycle: One litter of one or two born in late June, the result of delayed fertilization from fall mating. 50 -60 day gestation with weaning and flying at four weeks. Sexually mature, often mated, by first fall. (Forsyth says 1 to 3 years.)  Life span up to 12 years.

Remarks: The only bat in its genus.  Can be considered a northern species, summering in the north woods.  Summers in Canada and across the northern states as far south as New York.  Winters south of Pennsylvania. However, migration is somewhat variable in nature.  While some will hibernate in northern areas, most go south. Males travel shorter distances north in the spring than females. For example, all summer records from South Carolina have been males.  West Virginia only has a few records of summer males and no summer breeding females, although females regularly are reported as spring and fall migrants.  Mammals of Virginia says no records are known of this bat from summer months.  It states that they hibernate in Virginia.  Records have them in Virginia from September to May.  Pennsylvania has no reliable reports of large winter or summer colonies of this bat, whose status of "undetermined" has been assigned by the PA Biological Survey.  Therefore its safe to assume breeding summer populations are found north of this Appalachian study area.  

BACK TO THE TOP OF CHIROPTERA

EASTERN PIPISTRELLE (Pipistrellus subflavus) (bat; almost, yellow beneath)

Appalachian Region Distribution: Throughout.
Continental Range: Eastern half of US.   Two subspecies recognized.
Abundance: One of the most common bats.  More common west of the Blue Ridge, than the Piedmont and Coastal Plain.
Size and Molt: Head and body is 1.7 - 2.0"; 0.11 - 0.21 oz. The smallest bat in the east.
Mammae: One pair
Habitat: Forested areas.  Summer roosts in clumps of leaves, caves, rock crevices.  Found near openings of caves where more light is available than is tolerated by most bats. Winter hibernates in warmer back rooms where winter temperatures remain relatively constant. Both male and female winter together in caves, usually near their summer homes (the greatest recorded distance being 33 miles).
Active Period: Nocturnal. One of the first bats out in the evening.  It is often found during the summer in open woods near water.   Like the small-footed bat, the eastern pipistrelle is one of the last bats to enter hibernation (late October) and one of the first to leave in the spring.
Diet: Moths, flies, beetles, mayflies and caddis flies. Often forages over water.
Social Structure: In spring, females are solitary or form small nursing groups (usually less than a dozen; up to 35) in buildings and in hollow trees, often using several alternate roosts.  Males are solitary until fall mating and communal gathering with females at winter hibernaculum.  Some hibernate at summer location; other migrate up to 80 miles. Females arise from hibernation before males.  Fairly sociable, with small maternal groups of 30 or so remaining together for several years.  Although not colonial, can be found in winter caves, either solitary or in groups of several hundred.   Females tend to winter further south than males (Female to male ratio of hibernating pipistrelles increases to the south)
Life Cycle: Maternal spring colonies producing one litter of two young (rarely one or three -as mentioned in the life cycle of the hoary bat, I don't see how you can have three young with only two mammae) in June (from fall mating and delayed fertilization - although mating has been observed in winter and spring, especially among yearlings).  Probably fall mating involves adults over one year old, while spring mating involves mainly one year olds (with immediate ovulation).  In June to July, after a gestation period of 44 days, two young are born.  Young fly in three to four weeks, becoming sexually mature in a year. Life span up to 15 years for males, females seldom reaching 10 years.

Remarks: Has diagnostic weak, slow and erratic "moth-like" flight. One of the deepest hibernators; not easily disturbed. During hibernation, bats in the deep south (south of our Appalachian study area) will occasionally exit the cave to defecate; then returning to one of several favorite sites within the hibernaculum.  In Virginia, considered the least specialized cave bat; able to hibernate in the widest range of temperatures, humidity and cave configurations of any other bat.

Leopard frogs and hoary bats are known to feed on eastern pipistrelles.   

There are 68 species in this Pipistrelles genus.

BACK TO THE TOP OF CHIROPTERA

BIG BROWN BAT (Eptesicus fuscus) (house flyer; brown)

Appalachian Region Distribution: Throughout.
Continental Range: From southern Canada to Colombia and Venezuela.  Two subspecies described in the eastern US, with only one in the Appalachian region.
Abundance: Found throughout the region, but not in large numbers.
Habitat: Known to coexist well with man.  Summer roosts in large groups, originally in hollow trees, now in buildings, attics, as well as hollow trees and under loose bark and rock crevices. Winters (from only December to March) in buildings and well-protected roosts in caves and mines.
Size and Molt: Head and body is 2.4 - 3.1"; 0.49 - 0.74 oz.  Females slightly larger than males.
Mammae: One pair.
Active Period: Nocturnal. Emerges about sunset with slow, ponderous, fluttering flight and generally feeding near the ground at lower levels than those of bats with a rapid, erratic flight.  Does not generally migrate far, with an average distance of under 20 miles.   One of the last to disappear in the fall.  Can be seen during the day in winter.   In caves, are normally found near the entrances in partial daylight.  Normally not found in wintering groups of over 100 (NAS says usually in groups of one to five).  Apparently hibernates in buildings, trash piles, and other manmade shelters.  Hibernation is not profound and occurs only from December to April.
Diet: Due to large size, eats mainly hard insects, such as beetles, wasps, tree borers, and most other flying insects.  Midwest populations are known to feed on June bugs, green stinkbugs and cucumber beetles.  Seldom eats moths.  Forms a large brown fat layer in fall for winter consumption (up to a fourth of the bat's total body weight).
Home Range: Most spend their lives within a ten square mile area.
Social Structure: Like most bats, females form nursing colonies (20 to 600, but normally about 50 to 100) in spring, separate from the solitary males (but often in the same building). These groups break up by mid-summer or later (September through late November) with males and females regrouping in late summer prior to winter hibernation. Winter colonies normally have more males than females.  They have good site fidelity and homing instincts.
Life Cycle: One litter of two born ( in the east - one is normal in the Rockies and westward) in June. Although delayed fertilization occurs, mating is known to occur throughout winter and into spring. Gestation of 60 days result in young on the wing at 21 to 30 days, and possible mating in the first fall. Life span up to 18 years, although 10 to 12 is more common.

Remarks: Although not a very common bat, by far the most likely one to fly in your house, as the genus name implies.  Also, this is the one most likely to be seen in winter, since it hibernates in buildings.  The large size and two-toned pelage make the big brown bat easy to recognize. Many studies of big brown bats in hibernation have been conducted. While normal awake body temperatures are 99 degrees, apparently the body temp matches the environment down to a temperature of 30 degrees while breathing can drop from 200 times a minute to once every four to eight minutes.  A study in 1961 moved bats 20,40,100 and 250 miles from their home roosts.  They all returned, the furthest returning by the fourth and fifth nights.  Another study had bats return from 450 miles away from their home territory, probably using celestial navigation.

This big bat is very cold-tolerant, enabling it to enter hibernation later than most bats and migrate comparatively short distances.  

There are 19 species in this big brown bat genus.

BACK TO THE TOP OF CHIROPTERA

EVENING BAT (Nycticeius humeralis) (night, belonging to; upper arm, pertaining to)

Appalachian Region Distribution: This bat is not generally a mountain species. (PA is northern limit of range.)  More of a southern/piedmont-coastal plain species. 
Continental Range: All of southeastern US, except the Appalachians. Two subspecies described in the eastern US, with only one in the Appalachian region.
Abundance: Uncommon in our Appalachian study region.
Size and Molt: Head and body is 1.8 - 2.5"; 0.25 - 0.35 oz. (Females average a little larger than males.)
Mammae: One pair
Habitat: Natural and cultivated clearings as well as woodlands.  Woodland species roosting in hollow trees and under bark, also culverts, attics, abandoned barns, under bridges.  Evening bats almost never enter caves. 
Active Period: SE Mammals says out in early twilight, therefore, often seen by humans. Mammals of Ca, Va and Md says out well after dusk.  Mammals of Virginia says near dusk, with first flights at a height of 36 to 60 feet, but coming much lower as darkness falls.  Migrates in fall and winter. 
Diet: Moths, beetles, leafhoppers, flies and flying ants.  One Indiana study found that the largest single item (14%) was the spotted cucumber beetle.  Secondary food items were carabid beetles, stinkbugs, and chinch bugs.
Social Structure: Often found in large colonies. As with most bats, females give birth in nursing colonies (normally two young) at summer roosts in late spring or early summer (groups of 6 to 950; more commonly 25 to several hundred), while males remain separate. Males remain principally in the southern parts of the range.  Winter residency is not known.
Life Cycle: Usually two born in one litter at summer roost (May - June) from fall mating months (delayed fertilization). Young fly at 3 weeks, weaned at 6 weeks. Life span of 10 - 12 years (Mammals of Virginia and Novak say normally two years, with some records of individuals living over five years).

Remarks: Hibernates in deep south. Not much known about this species.  Only two species belong to this genus.  The other species is found in Cuba.

BACK TO THE TOP OF CHIROPTERA

RAFINESQUE’S BIG-EARED BAT (Plecotus rafinesquii) (twisted ear; Dr. Rafinesque)

Appalachian Region Distribution: Southern West Virginia, North Carolina and south.  Not currently known to reside in Virginia mountains.
Continental Range: Mainly a SE US, low elevation species.  Two subspecies described for the eastern US.
Abundance: Uncommon to rare in our Appalachian region.   (The subspecies, Plecotus rafinesquii rafinesquii, is considered a state endangered species in its coastal plain habitat in Virginia.)
Habitat: Forests, in hollow trees and under loose bark, but more often prefers old buildings, especially dilapidated cabins in deep woods.  Has a night roost different from the day roost.   Found at lower elevations than the Townsend’s Big-eared Bat.
Size and Molt: Head and body, 2.0 - 2.1" ; 0.21 - 0.35 oz, with females slightly heavier than males.
Mammae: One pair
Active Period: Becomes active late at night. Hibernates in caves from November to March in the Appalachians (northern part of its range).   They do not migrate, but are permanent residents throughout their range.
Diet: Moths are the primary food (90% in some studies).
Social Structure: Females form nursing groups of a few to several hundred (near the large extreme in the northern range; that being the southern Appalachians), with males being solitary or in small groups at this time. Both sexes roost singly, or may share communal winter hibernaculums, containing clusters of 2 - 100, with females outnumbering males.
Life Cycle: One litter of one born (late May/early June) in female nursing colonies of a few to several hundred females from fall/winter mating. Fly at three weeks, weaned at eight weeks, breeding at one year, with a life span of ten years.

Remarks: The common name says it all.  Formerly called Eastern big-eared bat. Notice similarities with the Townsend’s big-eared bat, of the same genus.  Wilson and Reeder recognizes the generic name Corynorhinus for both this species and the next one.  On-going debates on whether these New World bats should be classified in the genus Plecotus or Corynorhinus.  W/H and Mammals of Virginia chose the later, but the North American checklist (Jones) puts the New World big-eared bats in the former and the Old-World big-eared bats in the later genus.  Becoming quite rare; should be considered for threatened or endangered status.  

The ability to hover like a butterfly enables this moth specialist to pluck insects from foliage.  Its large ears are coiled against the side of the head, like a ram's horns, when at rest.

BACK TO THE TOP OF CHIROPTERA

TOWNSEND’S BIG-EARED BAT (Plecotus townsendii) (twisted ear; J. K. Townsend)  

FWS Endangered Species File