Key to bats of Colorado (version 2. Schorr and Navo 2014). This revised key includes diagrams and pictures to aid in species identification in Colorado. Please review and let us know if this key matches dichotomies that you have used.
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CALIFORNIA MYOTIS Myotis californicus
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Recognition
This is a small, pale-colored myotis with dark ears. The hairs of the dorsum are yellowish brown and lack burnished tips. The braincase rises abruptly above the rostrum. Total length of nine individuals from northwestern Colorado averaged 83.4 mm, length of forearm averaged 33 mm and weight averaged 4.8 g. Wingspan is about 210 mm. The only other Colorado myotis as small as the California myotis is the western small-footed myotis, which may be darker brownish in color, has dorsal hairs with brassy, burnished tips, a smaller hind foot and a skull with a flat profile, the forehead rising gradually from the rostrum. Care is needed to distinguish the species in the field, and certain identification requires comparative material in the museum.
Distribution
Like a number of other species of myotis, this is a bat of western North America, ranging from central Mexico north to British Columbia and from the Pacific Coast to Colorado, where it occurs at lower elevations in valleys and canyons along the Western Slope.
Habitat and Habits
This is a species of semi-desert habitats, including pi-on-juniper woodland and desert scrub. The animals roost by day in crevices, mines, caves, buildings, beneath bridges or behind loose bark. Night roosts include trees, shrubs and structures such as porches, eaves and outbuildings. Night roosts are dark and sheltered from wind. There may be local movements to suitable hibernacula in caves and mines, but long-distance migration is not known. The winter range of Colorado’s population is unknown, but the animals probably hibernate in the state.
Breeding
Copulation occurs in fall, and sperm are stored over winter by the female. Fertilization and implantation take place in spring. Just when implantation occurs is not known, so the gestation period has not been calculated, but probably it is about six weeks. A single young is born to a female in a nursery colony perhaps in May or June or even later. Lactating females have been captured in Colorado as late as August.
Food
The California myotis emerges in early evening to feed, just after the tiny western pipistrelle, which has a butterfly-like flight. It forages in arroyos, gaps between trees and near boulders and cliffs. It is active until about midnight and then again about dawn. Typical food includes flies, moths and spiders.
Remarks
This bat appears uncommon in Colorado except locally in the canyon country at lowest elevations on the Western Slope. Its biology here is poorly understood.
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WESTERN SMALL-FOOTED MYOTIS Myotis ciliolabrum
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Recognition
A small bat with a very small (8 mm) foot and dull to burnished brown pelage. The ears are dark, nearly black, and a distinct facial mask is frequent. It is almost impossible to distinguish from the California myotis, and only specialists can tell them apart with certainty. Total length, length of forearm and weight are 80 mm, 30 mm and 4 g, respectively. The wingspan is about 220 mm.
Distribution
This bat is widespread and common in the western United States. In Colorado it occurs statewide in suitable habitat. It seems to be most common in the canyon country of the Western Slope and in rocky areas of northeastern and southeastern Colorado.
Habitat and Habits
Despite its wide occurrence, little is known of habitat preferences of this species, although it is known to inhabit rocky areas and is more common at lower elevations. Summer roosts are highly variable and include buildings, mines, under bark on trees, beneath stones and a variety of other sites. The small-footed myotis is a year-round resident of Colorado. It hibernates in caves and mines alone or in small groups. Despite its small size, it is known to hibernate in open tunnels at low temperatures and low humidity, a situation one would assume is stressful. It sometimes hibernates near other bats, including Townsend's big-eared bat, at elevations to 9,500 feet.
Breeding
Little is known about the reproduction of small-footed myotis. Small nursery colonies of 10 to 15 are found occasionally in caves, mines or buildings. One young per year is usual. Young are born in mid-June following a gestation of about two months.
Food
The western small-footed myotis feeds early in the evening on small flying insects such as flies, small beetles and winged ants. This species is highly maneuverable in flight, often foraging among boulders, along cliffs or shrubs and trees.
Remarks
Like most species of Myotis, the small-footed myotis is often misidentified. It can be confused with the western pipistrelle or other mouse-eared bats, especially the California myotis. Earlier information on this species in Colorado was published under the names Myotis subulatus or Myotis leibii.
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LONG-EARED MYOTIS Myotis evotis
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Recognition
This species has the longest ears of any myotis found in Colorado. Black membranes contrast with the medium yellowish-brown fur. The belly is paler than the back. Hairs are lead-gray at their bases. Length averaged 86.4 mm, length of forearm averages 37.6 mm, and weights average 6.1 g. The wingspan is about 275 mm. The only species with which the long-eared myotis might be confused is the fringed myotis, which has shorter, narrower ears and a conspicuous fringe of stiff hairs on the trailing edge of the uropatagium.
Distribution
Like the Yuma myotis, this species ranges from central Mexico north to British Columbia, but it ranges farther east to the western edge of the Great Plains, including the western Dakotas and Nebraska. This species occurs at moderate elevations throughout the western three- fifths of Colorado, at elevations from 5,000 to 9,800 feet.
Habitat and Habits
The long-eared myotis is a species of coniferous forest, on both sides of the Continental Divide. Ponderosa pine woodland is the most common habitat type, although the animals also range down into piñon-juniper woodland, where they may be abundant. Roosts are in trees (often behind loose bark), caves, abandoned mines and other such sheltered areas. It is possible that the long-eared myotis hibernates in Colorado, as late fall activity has been documented in mines and caves, but individuals never have been found in winter.
Breeding
Reproduction has not been studied in detail, and dates of breeding are unknown. Males with scrotal testes have been captured in July, August and September. Females form small nursery colonies of one to three dozen individuals. In Colorado, pregnant females are most common in June and July. Lactating females have been captured in June, July and August. A single young is born. Probably, the gestation period is 50 to 60 days, as in other species of myotis of similar size.
Food
The long-eared myotis emerges after dark to forage near trees or over water. The animals are gleaners, hovering to take prey from leaves in forest gaps and edges. Principal food items are moths, flies, spiders and beetles.
Remarks
The long-eared myotis is not uncommon in parts of Colorado, but little is known of its biology here or elsewhere over its range.
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LITTLE BROWN BAT Myotis lucifugus
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Recognition
This is a relatively nondescript, medium-sized, small-eared bat best recognized by eliminating the several more distinctive species that might be confused with it. The Yuma myotis is of similar size but is paler in color and the hairs lack metallic, burnished tips. The California myotis may be as dark but is considerably smaller; the long-legged myotis is a heavier bat with a keeled calcar (a spur of bone that projects inward from the ankle) and a wing that is furred beneath from body to elbow. The fringed myotis has longer ears (as has the long-eared myotis) and a distinctive fringe of stiff hairs on the trailing edge of the uropatagium. Average length is 97.9 mm; average length of forearm is 39.3 mm. Weights average about 7 g, and the wingspan is about 220-270 mm.
Distribution
The little brown bat ranges across North America, from Alaska across Canada to Newfoundland and south, mostly in forested areas, to central Mexico. In Colorado the species may occur statewide in suitable habitat, ranging as high as 11,000 feet in Lake County. However, in the eastern two-fifths of the state, there are actual records only from Greeley and Pueblo.
Habitat and Habits
This is a species of wooded areas -- including riparian woodland in the mountains and lower valleys -- urban areas, woodlots and shelterbelts. The little brown bat is one of the most tolerant of bats in terms of roost selection. Night roosts are located in tree hollows, beneath tree bark, in or under buildings, bridges, crevices in rock, behind shutters or beneath eaves. They may share roosts with other species of bats. Day roosts in attics may be used by large concentrations of bats. Hibernation sites include caves, mines and buildings. Some little brown bats hibernate in Colorado, but winter habits are poorly known here and elsewhere in the West. In Ontario, hibernation lasts from September to May. In some parts of the range, the animals may move several hundred kilometers from nursery colonies to hibernacula, but such long-distance movements have not been documented in the West. The animals can move 50 miles a night at speeds up to 19 miles per hour. Maximum longevity in these bats may be remarkably long; the current record is some 31 years. The average lifespan, however, is much shorter, as over half the young die in their first year. Predators include raccoons, mink, snakes and owls.
Breeding
A great deal is known about the breeding habits of the little brown bat in the eastern part of its range, but the species has not been studied intensively in the West. Breeding takes place in autumn or early winter. There are two phases, an active phase in which males and females are alert and a passive phase in which males mate with torpid females. Breeding of both sexes is promiscuous. Sperm are stored by the female in the uterus until spring, when fertilization, implantation and gestation take place. Gestation lasts 50 to 60 days, depending on temperatures. The young are born almost always singly in nursery colonies from late May to early June. At birth, little brown bats are blind, but their eyes open in two days. The mother can fly with her offspring attached to a nipple, but the young usually is left in the roost during the mother's foraging flights. Young can fly on their own by 3 weeks and reach adult weight about a month after their first flight. About half the females breed their first autumn. Males breed first as yearlings. Nursery colonies of several hundred females are known. Non-breeding females and males roost away from nursery colonies.
Food
Little brown bats emerge at dusk to feed, often following the same foraging route repeatedly through the night and on successive nights. They forage over water or among trees, 3 to 6 meters above ground. Foraging flight is erratic for a bat of this size. The diet consists largely of aquatic insects, including caddis flies and midges, but also includes moths, mosquitoes and other flies. The prey is knocked from the air with a wingtip, captured in the membrane between the legs and lifted to the mouth. Foraging behavior has to be learned, and adults are much more efficient feeders than are young; adults fill their stomach in as little as 15 minutes.
Remarks
This is perhaps the most common, widespread bat of temperate North America, and it is one of the best studied. It deserves greater attention in Colorado, however, particularly because former colonies have disappeared or have been reduced in size.
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FRINGED MYOTIS Myotis thysanodes
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Recognition
The fringed myotis is distinguished by its relatively long ears and a conspicuous fringe of stiff hairs on the trailing edge of the uropatagium. The pelage varies in color from pale to rich brownish, individual hairs being lead-gray at their bases. The membranes are dark. Total length of five individuals from northwestern Colorado averaged 86.8 mm; length of forearm averaged 40.1 mm: and weight averaged 7.5 g. The wingspan is 265-300 mm. The only other medium-sized myotis with long ears is the long-eared myotis, a species in which the ears are 21-24 mm long (by contrast with ears 17-20 mm long on the fringed myotis).
Distribution
This is a western species, ranging from the Isthmus of Tehuantepec in Mexico north to British Columbia, Montana and Wyoming. The animals apparently occur as scattered populations at moderate elevations on the Western Slope, along the foothills of the Front Range and the mesas of southeastern Colorado. Maximum elevation is 7,500 feet.
Habitat and Habits
The fringed myotis is a species of coniferous forest and woodland at moderate elevations in Colorado. Records of occurrence are few, and the species isn't common in the state, but perhaps it is simply widely distributed. Typical vegetation of the habitat includes ponderosa pine, pi-on, juniper, greasewood, saltbush and scrub oak. The animals roost in rock crevices, caves, mines, buildings and trees. They are known to hibernate in caves and buildings. Where this species has been studied well, migration seems not to be extensive.
Breeding
Breeding takes place in fall; ovulation, fertilization, implantation and gestation occur in spring, as sperm are stored over the winter in the female's uterus. Up to several hundred females congregate in nursery colonies. Males are solitary while the young are reared. In a typical season, all mature females breed. The single young is produced after a gestation of 50 to 60 days. Newborn young are hairless and pinkish, and their eyes are closed. Growth is rapid, however, and they can fly by 20 days old. Maximum known longevity is 11 years. Although some individuals may live even longer, the average lifespan is much shorter than that.
Food
The fringed myotis feeds on such arthropods as moths, daddy longlegs and beetles. They forage along water, above shrubs and woodlands or low over meadows (apparently in more open areas than the long-eared myotis), emerging to feed about two hours after sunset. Flight speeds average about 9 miles per hour.
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LONG-LEGGED MYOTIS Myotis volans
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Recognition
This is Colorado's only medium-sized, short-eared myotis with a keeled calcar (the spur of bone that projects inward from the ankle and helps to support the uropatagium). It is a fairly heavy-bodied bat, and the medium to dark brown fur on the back extends to the tail membrane. The short ears appear more round, less pointed than those of other species. Hairs of the venter are paler than those of the back and may even be buffy. The underside of the wing usually is well furred to the elbow. Tips of individual hairs may appear slightly burnished. Mean measurements of six males and nine females from Park County were: length, 97.3 and 102 mm; length of forearm, 37.8 and 38.2 mm; weight, 8.7 and 11.2 g. The wingspan is 250-270 mm. The species most readily confused with the long-legged myotis is the little brown bat, which differs in having relatively longer ears, lacking the distinct keel on the calcar and frequently having paler pelage.
Distribution
This species occurs throughout much of western North America from central Mexico to extreme northwestern British Columbia and from the Pacific Coast to the western margins of the Great Plains. The animals occur across the western three-fifths of Colorado and the wooded mesas of southeastern Colorado at elevations ranging from about 5,000 to 11,500 feet. This is the most common myotis at higher elevations in the state.
Habits and Habitats: The long-legged myotis is a species of wooded areas in foothills, mountains and high plateaus. Typical habitat is montane or subalpine forest, ponderosa pine woodland, piñon-juniper woodland and montane shrubs with willows or well-watered stands of sagebrush. The animals roost by day in buildings, mines, fissures in rocks or beneath loose bark on trees. Usually they roost singly or in small groups. Night roosts are in dark places like caves or mines. Winter haunts of Colorado individuals are unknown, but they may hibernate locally, with only short migrations, as late fall activity has been observed at mines and caves. Elsewhere, they are known to hibernate in mines or caves.
Breeding
Pregnant females form small nurseries of up to several dozen individuals in buildings, crevices or trees. Males are segregated and solitary during the maternity season. In Colorado, males with scrotal testes have been captured in July and August. It has been noted that the long-legged myotis has a particularly long parturition season. Pregnant females have been noted from June to early August in Colorado and elsewhere, and births are spread throughout the summer. Lactating females are most abundant in samples beginning in August. Females apparently breed their first winter. Reproduction in this species has not been studied in detail.
Food
The long-legged myotis mostly eats moths. They emerge to feed early (while it is light enough to observe them distinctly) and forage at heights of 3 to 4 meters over ponds, streams, open meadows or forest clearings, cruising a repetitive circuit through the evening. Flight is more relaxed and leisurely than that of other medium-sized species of Myotis, and experienced observers can distinguish it by the flight pattern.
Remarks
This is one of our most common bats, and it deserves intensive study in Colorado. Of particular interest would be some knowledge of its breeding biology, population trends, and winter distribution.
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YUMA MYOTIS Myotis yumanensis
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Recognition
This is a medium-sized, small-eared, pale grayish to reddish or yellowish bat, its dark membranes contrasting fairly strongly with the fur. Among Colorado's species of Myotis, only the California myotis and the small-footed myotis are as pale in color. The small-footed myotis is more yellowish, less grayish and both it and the California myotis are smaller than the Yuma myotis. Total length is 86-88 mm; length of forearm, 34-38 mm; and wingspan, about 235 mm. Weight ranges from 3 to 5 g. This bat may be confused with the little brown bat, Myotis lucifugus in the field.
Distribution
The Yuma myotis occurs widely in western North America, from central Mexico north to British Columbia, Montana and southeastern Colorado. In Colorado these bats occur at moderate elevations in valleys on the Western Slope, in the San Luis Valley and on the eastern slope north to the vicinity of Colorado Springs. They don't seem common. Maximum reported elevation of occurrence in Colorado is about 7,900 feet at Conejos in the San Luis Valley.
Habitat and Habits
This is a species of dry shrubby country, but it appears to be tied more closely to water than any of Colorado's other bats. Typical habitat is in piñon-juniper woodland and riparian woodland in semi desert valleys. The animals roost in caves, crevices or abandoned buildings and other structures. They forage over water, along streams, over springs, among riparian or shoreline vegetation. The Yuma myotis apparently does not hibernate in Colorado, but its winter haunts are unknown. They arrive in Colorado about April, and they become scarce in September.
Breeding
Breeding has not been studied much in Colorado, although lactating females have been captured and a nursery colony was discovered in 1990 in the Colorado National Monument. Elsewhere, the animals are known to form nursery colonies of upwards of several thousand individuals in caves or attics. Apparently all adult females in a population breed. A single young is born late in the spring or early in the summer. Small breeding colonies have been discovered in the southeastern part of the state, but not elsewhere in Colorado. Males are solitary as the young are reared.
Food
Food consists mostly of moths, flies and beetles, but also includes leafhoppers, caddis flies, lacewings and crane flies. The animals forage near water and take many aquatic insects. They are efficient feeders and can fill their stomachs in 15 to 20 minutes. They forage in early evening, usually along the main channel of a stream.
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EASTERN RED BAT Lasiurus borealis
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Recognition
As the name indicates, this is a colorful bat, varying from bright reddish orange to yellow. It is a medium-sized bat with long (300 mm) pointed wings and a distinctly long tail and uropatagium. Average measurements of 11 females from Kansas were: total length, 114 mm; forearm, 53 mm.
Distribution
Mostly a species of the eastern United States, the red bat also occurs in the southwestern U.S. and Mexico. In Colorado, it apparently is rare, and mostly is found in riparian woodlands (and artificial extensions such as urban landscaping) along the South Platte and Arkansas rivers and major tributaries.
Habitat and Habits
The red bat is solitary and roosts by day in deciduous trees, such as cottonwoods or fruit trees. It seems to prefer American elms where it hangs among the leaves. Red bats usually are well hidden and only can be seen from directly below. They usually roost 4-10 feet off the ground unless they have young, in which case they will be found up to 20 feet high in the tree. Red bats are highly migratory and migrate in groups. Males and females apparently migrate separately, however. Hibernation occurs in the southern states (not in Colorado) where these bats may arouse and forage throughout the winter. Predators include opossums, domestic cats, hawks and owls.
Breeding
Breeding occurs in the fall. Sperm cells are stored by the female until spring when ovulation and fertilization occur. Gestation takes 80 to 90 days. The red bat typically gives birth to twins (although four young are known) in the early summer. The young are carried by the female from one roost to another and occasionally on feeding flights. Offspring are cared for until they are nearly fully grown. Some reports indicate that the mother carries the young until their weight equals her own. Young red bats are weaned in 4 to 6 weeks and can fly at 3 to 6 weeks of age.
Food
More than other bats, red bats seem to take advantage of insects attracted to lights, and they often are found feeding near street lamps where they appear to be territorial. They alight and feed on non-flying insects, including grasshoppers and crickets. They feed near moth-infested areas, which is certainly a benefit to humans. Foraging occurs in early evening when they leave their roosts and fly in high, lazy patterns over the trees and along forest edges. When it is dark, they descend and feed below the treetops to within a few feet of the ground.
Remarks
The unusual hibernating behavior of this species is of special interest to science. Red bats survive at subfreezing temperatures and are able to arouse readily from deep sleep. -
Recent citations
Neubaum, D. J. 2005. Records of the eastern red bat on the northern Front Range of Colorado. Prairie Naturalist 37:41-42.
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HOARY BAT Lasiurus cinereus
Recognition
The hoary bat cannot be mistaken for any other species. The tips of the hairs are white or grayish with brown shafts giving a frosty or hoary effect. The ears are short and round with a striking black border. This is one of Colorado's largest bats with a wingspan of about 400 mm, a body and tail about 140 mm long, and a forearm 50-58 mm long. Hoary bats weigh approximately 25 g.
Distribution
The hoary bat is widespread, ranging from northern Canada to Guatemala, and probably occurring in all states except Alaska -- even in Hawaii, where it is the only native land mammal. In Colorado, the hoary bat probably occurs statewide from the plains to timberline.
Habitat and Habits
The hoary bat is a solitary, tree-roosting species and can be expected to live in any habitat with trees. It is migratory with the sexes migrating north together in spring. During summer, the sexes separate, however, perhaps to reduce competition for food while females give birth and rear the young. Hoary bats arrive in Colorado in April and are gone by November. There is no record of hibernation here.
Breeding
Most females give birth and raise their young in northern and eastern North America, although a few females rear young in Colorado. Litter size is generally two with a range of one to four. Birth occurs between May and July. The mother can forage with the young clinging to her nipple, but generally the young are left at the roost site. Young begin to fly at about 30 days of age. Copulation usually occurs during the fall migration but may take place on wintering grounds. Implantation of the new embryos is postponed until spring when growth and development are completed.
Food
The hoary bat prefers moths but also feeds on beetles, wasps, grasshoppers and even small bats. An open-air forager, the animals seem to approach moths from the rear, severing the abdomen and thorax from the rest of the body. Flight is swift and direct, and a keen observer can readily identify the hoary bat by its flight pattern, body size and relatively long, narrow wings. It tends to emerge later in the evening to forage than most other local bats. In Colorado its foraging period seems to be varied, however, due to the vagaries of local weather. The hoary bat can often be seen foraging with the big brown bat near street lamps or other outdoor lights.
Remarks
Little is known about the natural history of this species in Colorado; it deserves more study.
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SILVER-HAIRED BAT Lasionycteris noctivagans
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Recognition
A medium-sized bat with black hair tipped in silver or yellow; the silver-haired bat is one of Colorado's most distinctive and attractive mammals. Wingspan ranges from 270 to 310 mm. Average measurements of 10 males from northwestern Colorado were: total length, 104 mm; forearm, 39 mm; and weight, 12 g.
Distribution
This is a northern species that occurs throughout Alaska, Canada and all of the contiguous United States except Florida. In Colorado it is found statewide but is more common in the forested mountains at elevations up to 10,000 feet.
Habitat and Habits
The silver-haired bat is usually solitary, but it is occasionally found in pairs. It roosts in
trees, under bark, under rocks and infrequently in
open soft-walled caves or mines. Silver-haired bats also roost in open buildings,
such as sheds or garages. It is seldom found in closed structures, such as the attics
of houses. This bat occasionally has been found hibernating in mines in Colorado
but probably usually migrates elsewhere to spend the colder months. Field data indicate
the silver-haired bat is most abundant during late spring and early fall when both
sexes are found in the state. Predators include skunks, owls and probably snakes.
Breeding
Little is known of the reproductive habits of this species. Two young are produced in early summer. Mating probably occurs in autumn with the female storing sperm during the winter. Ovulation occurs in April or May. Gestation is 50-60 days. There is some evidence that the sexes are segregated during summer. Silver-haired bats occasionally form fairly large nursery colonies of 200 or more females and their young.
Food
Like all Colorado bats, the silver-haired bat is an insect-feeder, preferring moths, flies, beetles and wasps. The silver-haired bat is a slow flyer, often seen foraging near the ground. It commonly flies around ponds and woodland streams.
Remarks
The slow flight of this bat is unusual. The animals are hooked occasionally by anglers fly-fishing. Because silver-haired bats roost in tree hollows and behind loose bark, clear-cutting and removal of standing dead trees may affect their distribution and abundance.
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CANYON BAT formerly WESTERN PIPISTRELLE Parastrellus hesperus
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Recognition
The canyon bat is the smallest of Colorado's bats. It is easily recognized by its slow, erratic, butterfly-like flight. It has short, black ears, grayish brown pelage and a distinctive black mask. It is one of the most attractive bats in North America. It weighs less than 4 g, little more than a penny. Other measurements are: wingspan, 190-215 mm; total length, 68-75 mm; and forearm, 29-31 mm.
Distribution
This species is found throughout the desert southwest. It ranges as far north as Washington state and east to Oklahoma. In Colorado, it is found at lower elevations on the Western Slope and in the extreme southeast.
Habitat and Habits
This is a bat of the desert. It lives in arid canyons or dry shrub lands, near water. The western pipistrelle rarely roosts in human-made structures, nor does it seem to use mines or caves much except as hibernacula. It does roost in dense vegetation and beneath rocky slabs. Although the canyon bat doesn't use the same roost day after day, it roosts in the same general area. Day and night roosts are different. This bat is non-migratory and sedentary. The only hibernaculum discovered to date in Colorado was in a gold mine at 9,500 feet in the La Plata Mountains above Mancos. Predators are probably snakes, birds of prey and other bats.
Breeding
One or two young are born in June each year. The canyon bat was confirmed to breed in Colorado when an infant bat was discovered on the floor of an abandoned building at Rio Blanco Reservoir, and a lactating female and a juvenile were observed at the Colorado National Monument. These bats may form small nursery colonies of 20-50 females and young. The young are very small and exhibit the black mask at an early age. Males are segregated from females during much of the summer. Copulation occurs in the hibernaculum, followed by ovulation in spring.
Food
Canyon bats eat small moths, beetles, mosquitoes and other flies. The western pipistrelle emerges very early to forage, sometimes before sundown, and again in early morning. The animals forage near canyon walls and among scattered boulders and shrubs. They remain active throughout the year. Foraging seems to be limited by winds above 10 mph.
Remarks
The size of this bat can only be appreciated at close range. In the air, it appears fragile. The slightest breeze blows it off course or causes it to stall.
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TRI-COLORED BAT (formerly EASTERN PIPISTRELLE) Perimyotis subflavus
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Recognition
Slightly larger than the canyon bat, the tri-colored bat is readily distinguished by its tri-colored dorsal hairs, dark brown at tips and bases with a band of yellow between. Measurements include: total length, 70-90, forearm, 30-35, wingspan about 210; weight 5-8 g.
Distribution
This is a bat of eastern North America, ranging from Nova Scotia and Minnesota south to Mexico, Guatemala and Belize. There are a couple records of this bat from eastern Colorado.
Habitat and Habits
The tri-colored bat is an animal of open deciduous forests. The animals are not strongly migratory, typically spending the summer in the same general region as the hibernaculum.
Breeding
Adults in reproductive condition have been captured in the southeastern U.S. in winter and spring. Twin births are the rule in late spring or early summer.
Food
Tri-colored bats emerge early, while still light, to forage in clearings or over still water for smaller insects, including moths, flies and beetles.
Remarks
The number of records of this species in Colorado suggest that until information to the contrary develops, the conservative course is to consider it an accidental occurrence.Return to top -
Recent citations
Armstrong, D. M., R. A. Adams, and K. E. Taylor. 2006. New records of the eastern pipistrelle (Pipistrellus subflavus) in Colorado. Western North American Naturalist 66:268-269.
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BIG BROWN BAT Eptesicus fuscus
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Recognition
This is a large bat with medium-sized, rounded ears. The wings are long (325-350 mm) and powerful. Color is always some shade of brown, varying from russet to almost black and chocolate. This is the most commonly seen bat in Colorado. Average measurements of 10 females from Fort Collins were: total length, 115 mm; forearm, 48 mm; and weight, 17 g.
Distribution
The big brown bat is found widely in the New World, from Alaska to South America. It can be found throughout the United States in a variety of habitats. In Colorado it can be encountered just about everywhere, especially in towns and cities associated with buildings.
Habitat and Habits
The big brown bat is more closely associated with humans and development than any
bat in North America. It is often found in cities and towns
and around structures. The big brown bat congregates in large groups in summer,
and when these groups take up temporary residence in an attic, they can be both
an annoyance and an effective control on flying insects. They also use rock crevices
for roosting. Temperature seems to be a factor in roost selection, females preferring
higher temperatures than males. Big brown bats are year-round residents of Colorado,
hibernating in mines, caves, fissures, storm sewers and a variety of other places.
Prior to hibernation, they store up to 30 percent of their body weight in fat reserves.
This bat has been studied widely for its remarkable homing ability. It can return
to its roost site from distances of over 400 miles in less than a month, and returns
of up to 40 miles in a single night are known. Predators include snakes, hawks,
owls, weasels, house cats, and raccoons.
Breeding
As with most Colorado bats, mating occurs in the fall, the sperm over winter in the female's uterus and the young are born in midsummer, following a gestation of approximately two months. In the West, a single young per year is the rule; twins are common in the East. Females congregate in colonies of up to 300 individuals. Mothers apparently can recognize their own offspring even in masses of newborn bats. When young bats occasionally fall to the ground or floor, there is evidence that mothers recover them and put them back in the roost. Female big brown bats will move their young from one roost site to another if disturbed.
Food
Big brown bats are generalist insect feeders. They eat a variety of larger, flying insects and beetles, even some too large for these bats to fly away with. Given their habit of living near humans, they are important in keeping urban insect populations under some control. Studies indicate that big brown bats eat many insects considered detrimental to humans. When big brown bats emerge to forage in the evening, they make a strong, straight flight at a height of 20-30 feet above the ground. This flight is highly predictable, and the groups can be seen at the same location for weeks at a time. Foraging is generally in open areas, where they may be seen with the hoary bat. The species probably do not compete, however, as their diets differ somewhat.
Remarks
The big brown bat is beneficial to humans, but it has suffered both because and in spite of itself. The insecticide DDT, once used in this country to control problem insects, is highly toxic to big brown bats. Ironically, a natural insect control was destroyed by humans in their efforts to control insects artificially.
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SPOTTED BAT Euderma maculatum
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Recognition
Colorado's rarest bat is perhaps its most striking. The spotted bat has enormous pink ears and three large white spots on the black dorsal surface. Measurements of a Colorado specimen are: total length, 119 mm; length of forearm, 52 mm; weight, 13.5 g.
Distribution
This species is known from scattered localities in western North America and apparently is one of the more difficult bats to capture, leading to a perception that this bat is rare in the United States. In Colorado, the spotted bat is known by published records from the vicinity of Dinosaur National Monument, and from a number of places at lower elevations on the Western Slope, including the Four Corners area where pregnant or lactating females have been captured. Further, acoustic records show that distribution of this species in Colorado is relatively widespread. Similarly, this species may be more widespread across the United States than previously thought.
Habitat and Habits
The spotted bat has been found in a variety of habitats, including ponderosa pine, piñon-juniper woodland and shrub desert. Early researchers suggested that this bat favored ponderosa pine forests, but more recent investigations suggest that the species may prefer areas with cliffs and water. The species appears mostly solitary, forming small nursery colonies or groups in hibernation. Little is known about hibernation or annual movement patterns, although they have been found in buildings in Nevada in September. Details of mortality are unknown, although known predators include kestrels and owls.
Breeding
Little is known of the reproductive biology of this species. A single young is born, probably in late May or mid-June. One newborn weighed 4 g, 25 percent of the weight of its mother.
Food
The preferred food of spotted bats is moths. Apparently only the abdomens are eaten as the spotted bat has been observed to remove and discard wings and heads of captured prey. Other food items include beetles, katydids and grasshoppers. Foraging occurs throughout the night, in open habitat, 5-10 m above the ground. The echolocatory calls are audible to humans.
Remarks
This species may be found in the major canyons along the western border of the state and southeastern Colorado. Its unique appearance should enable correct identification. Any sighting of the spotted bat should be reported to the Colorado Division of Wildlife.
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TOWNSEND’S BIG-EARED BAT Corynorhinus townsendii
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Recognition
This bat's ears are remarkable -- reaching a length of 38 mm. The face is marked by a large lump on either side of the snout. Color ranges from pale brown to slate gray. Females are larger than males. Measurements include: total length, 90-112 mm; length of forearm, 39-48 mm; and weight, 9-14 g. Wingspan is approximately 280 mm.
Distribution
This is a bat of western North America, ranging from southern British Columbia to
southern Mexico. Townsend's big-eared bat can be found throughout Colorado.
Its distribution seems to be determined by availability of roosts, such as caves,
mines, tunnels, crevices and masonry structures with suitable temperatures, making
the conservation of suitable roosts essential to the management of this species.
Habitat and Habits
This bat is generally solitary or gathers in small groups, although during summer females may form larger maternity colonies. Townsend's big-eared bat can be found in mines, caves and structures in woodlands and forests to elevations above 9,500 feet. They often hang near the entrances to roosts, in the "twilight zone." The animals do not make
major migrations and appear relatively sedentary.
Hibernacula have low and stable temperatures, sometimes with moderate airflow, during
late October to April. Hibernating, the bats hang singly or in small clusters in
the open, not in crevices, with pelage erect to provide maximum insulation and the
ears coiled back like a ram's horns, perhaps to reduce heat loss. The bat is quite
sensitive to changes in temperature and humidity within the hibernaculum and may
arouse to move to a more favorable location. Care should be taken not to disturb
them because paying the price of accidental arousal in winter could deplete energy
stores and prevent arousal in spring. Populations may be principally limited by
high winter mortality due to the absence of roosts with stable temperatures. Most
mortality occurs during the first year of life. Predators have not been documented,
but snakes, owls and hawks probably take these bats.
Breeding
Copulation, which occurs in late fall, is preceded by ritualized courtship behavior by the
male. The female stores sperm in the reproductive tract until spring
when ovulation and fertilization happen. Gestation takes 50-60 days. Young are born
in mid-June, and strong bonds form between mother and offspring. About 90 percent
of all females in the nursery colonies produce young. Young fly in 2 to 3 weeks
and are weaned by 6 weeks. Only one young is born per female.
Food
This bat feeds mainly on small moths, but also eats beetles, flies and wasps. Townsend's big-eared bat usually is a late flier (except for females from maternity roosts) and forages along the edge of vegetation. The animals sometimes glean insects from the vegetation. Like other species, this bat may use a night roost and then feed a second time just before dawn and the return to its day roost.
Remarks
Populations, especially in the nursery and hibernaculum, are highly susceptible to disturbance and have been reported to be declining. Little is known of the natural history of this species in Colorado, but the animals certainly stand to benefit from the Bats/Inactive Mines Project of the Colorado Division of Wildlife.
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ALLEN'S BIG-EARED BAT Idionycteris phyllotis)
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Recognition
The Allen's big-eared bat is similar in apperance to the Townsend's big-eared bat displaying disproportionately large ears and convoluted nasal folds. Since this species has yet to be captured in Colorado measurements are based on other locales. Total length is 103-121 mm; tail length is 46-55 mm; hindfoot length is 9-12 mm; ear length is 38-43 mm; forearm length is 43-49 mm; and wingspan is 31-34 mm (Armstrong et al. 2011).Distribution
Long believed to be a resident in Colorado it was not until 2008 when Mark Hayes and colleagues (Hayes et al. 2009. ). Currently, suggested range in Colorado is restricted to the southwestern counties.Habits and Habitats
The Allen's big-eared bat is associated with shrublands, ponderosa pine lands, and pinon-juniper woodlands, and has been captured in riparian cottonwood galleries. The recordings in Colorado were made along the La Sal Creek canyon in Montrose County.
Breeding
Little is known of the Allen's big-eared bat's reproductive ecology. In the spring, females segregate from males to form maternity colonies. Of the few maternity colonies known they ranged in size from 25 - 97 individuals and were in mine tunnels or a pile of rubble near a grotto. Females typically have 1 young that are volant by mid-summer (Czaplewski, N.J. 1983. Idionycteris phyllotis. Mammalian Species 208:1-4.)
Food
Allen's big-eared bats appear to be moth specialists, but also eat various beetles and ants. It is believed that they will glean insects off of vegetation and can take insects in flight (Czaplewski 1983).
Remarks
The Allen's big-eared bat tends to feed later in the evening and recordings from Colorado were made between 9 pm and 2:30 am (Armstrong et al. 2011). This species has not been captured in Colorado despite much effort by Mark Hayes and colleagues.
Recent citations
Hayes, M. A., K. W. Navo, L. R. Bonewell, C. J. Mosch, and R. A. Adams. 2009. Allen's big-eared bat (Idionycteris phyllotis) documented in Colorado based on recordings of its distinctive echolocation call. Southwestern Naturalist 54(4):499-501.
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PALLID BAT Antrozous pallidus
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Recognition
The pallid bat is a large, pale, rather long-eared bat, not easily confused with any other species. Their eyes are large, and their face is covered with wart-like sebaceous glands. Color varies from pale creamy to light brown. Average measurements of 12 individuals from northwestern Colorado were: total length, 107 mm; forearm, 56 mm; and weight, 19 g. Wingspan is approximately 380 mm.
Distribution
The range of the pallid bat extends from southern British Columbia to central Mexico and east to central Kansas and Oklahoma. In Colorado this bat inhabits lower elevations of the Western Slope, broken rocky areas of the southeastern part of the state and along the foothills to Colorado Springs. A report of an isolated colony at Torrington, on the plains of eastern Wyoming, suggests that the pallid bat could be found in rocky habitats
or structures on the plains of eastern Colorado.
Habitat and Habits
This is a species of deserts and grasslands near rocky outcrops. The pallid bat's habit of using structures built by humans may allow it to extend beyond what would otherwise be its natural range. In Colorado, the pallid bat occupies semidesert scrub and piñon-juniper woodlands to about 7,000 feet. Pallid bats are gregarious, although males may separate from breeding females in summer. Elsewhere, this species is not migratory and makes only short movements to hibernation sites. Pallid bats probably hibernate in Colorado from mid-October to April, although there is no direct evidence of their winter habits here. Pallid bats form small colonies and may use rock crevices as day roosts. These roosts are selected for suitable temperature and protection from predators. Night roosts are also selected on the basis of a temperature that minimizes energy loss. Night roosts, such as crevices, shallow caves, overhangs, and man-made structures, are usually near day roosts. Both day and night roosts change seasonally as their thermal characteristics change. Mortality is highest when young bats
are first beginning to fly. Their habit
of foraging on the ground makes pallid bats susceptible to injury and predation.
Predators include hawks, kestrels, owls and snakes.
Breeding
Copulation occurs between October and December, and sperm are stored by the females until spring, when ovulation, fertilization and implantation happen. Gestation is about 9 weeks. Older females generally give birth to two young, whereas younger females have only one. Young are born in June and July, and the sex ratio of the newborn is 1 to 1. Young begin to fly between 28 and 35 days old and are completely weaned at 6 to 8 weeks. Mothers forage with the young until the young become independent.
Food
The pallid bat feeds principally on flightless ground-dwelling arthropods, such as crickets, grasshoppers, beetles, scorpions and spiders. Their presence is revealed by audible clicks as they forage after full dark and again before sunrise. Other foods include large moths, lizards, small bats and small rodents.
Remarks
Social behavior of pallid bats is quite interesting. There is a strong bond between mother and offspring, and the association may continue year after year. There is also strong group cohesion and roost site attachment. Young are provided preferential positions in roosts, pregnant females are attentive to other females in labor and females actually signal mothers whose young are in distress.
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BRAZILIAN FREE-TAILED BAT Tadarida brasiliensis
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Recognition
This species is small and gray-brown with long, narrow wings and a tail that extends well beyond the membrane between the legs. Individuals weigh 8-12 g and have short ears that almost join at the midline of the forehead. Wingspread is approximately 300 mm, total length is 90 to 105 mm and the forearm is 36 to 46 mm long.
Distribution
The Brazilian free-tailed bat is one of the most widely distributed mammalian species in the Western Hemisphere. There are 9 recognized subspecies, with 2 occurring in the U.S. T. b. mexicana is primarily western, occurring from southern Oregon to eastern Nebraska and south through Mexico. T. b. cynocephala is primarily a southeastern species, from eastern Kentucky into South Carolina and south through Florida. T. brasiliensis ranges southward through most of Central America. In the western U.S., T. brasiliensis is most commonly associated with dry, lower elevation habitats, yet it also occurs in a variety of other habitats and is found up to 3000 m in some of the western mountain ranges
Habitat and Habits
The Brazilian free-tailed bat roosts in caves and mines and is often found in man-made structures. The animals are highly social. In Arizona, New Mexico and Texas, nursery colonies of 10 to 20 million individuals have been reported. Males generally form small colonies farther north, although a colony in Colorado has an estimated population of as many as 250,000 individuals. This bat does not hibernate in Colorado. The species is highly migratory and travels south to Mexico and Central America for winter. There may be distinct migratory pathways. Some apparently live to be 15 years old, but most have a considerably shorter life span. Predators include owls, kestrels, various hawks, raccoons, skunks and snakes.
Breeding
Brazilian free-tailed bats breed on their winter ranges. Gestation is 90 to 100 days, and a single young is born in mid-June or early July. Although most young are born south of Colorado, a few are produced here. At birth, infants weight 25 percent of the mother's weight, about 2.5 to 3 g. For many years it was believed that mothers in colonies of hundreds of thousands or even several million females probably did not nurse their own young, but simply fed the first young to grasp the nipple. However, it has now been demonstrated that females locate their offspring by auditory and olfactory cues. Young begin to fly at about 5 weeks and are weaned shortly thereafter.
Food
This bat eats mostly small moths, although beetles, bugs, mosquitoes and wasps are also taken. The large population of this species in south-central Colorado consumes tons of insects each year. The bats forage high over large open areas, leaving their roosts in a flight formation that resembles a long plume of dark smoke. They may forage up to 40 miles from their day roosts.
Remarks
Populations of this species are declining across their wide range. Reasons for the decline seem to be disease, pesticide poisoning and human disturbance of nursery colonies. As other bats, this valuable species deserves continued respect, study and protection.
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BIG FREE-TAILED BAT Nyctinomops macrotis
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Recognition
Like the Brazilian free-tailed bat, these animals have a tail that extends well beyond the uropatagium. This bat is much larger than the Brazilian free-tailed bat, and its ears join at the midline of the forehead. Color varies from pale brown to black. Wingspan is approximately 425 mm. Average measurements are: total length, 140 mm; length of ear, 25 mm; length of forearm, 60 mm.
Distribution
The big free- tailed bat occurs mainly in southern California, Arizona, New Mexico, Texas and Mexico. Long thought to be an accidental wanderer in Colorado, recent data show the presence of breeding colonies in Colorado. Indeed, audible echolocation calls and recordings provide evidence of widespread occurrence across Colorado.Habitat and Habits
This bat frequents rocky or canyon country where it roosts in crevices. This migratory species is a swift, powerful flier, and occasional individuals wander as far north as Canada. Little is known of mortality and longevity.
Breeding
Breeding probably occurs in midwinter while the species is in warmer latitudes. A single young is born in mid-June to early July. Females form small nursery colonies, and the young do not leave the nursery until they are almost full grown.
Food
Moths seem to be the mainstay of their diet, although little data has been collected. This bat emerges late in the evening and forages at high altitudes. The echolocatory calls are audible to humans.
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