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Lasiurus cinereushoary bat

By Susan Karen Anderson

Geographic Range

Hoary bats are the most widespread of all bats in the United States. Though not yet recorded in Alaska, these bats are thought to occur in all 50 states. They range from the tree limit in Canada down to at least Guatemala in Central America, and throughout South America. They are the only bats found in Hawaii. There are records of migrant hoary bats on Southampton Island off of Northern Canada, and from Iceland, Bermuda, and the Orkney Islands off Scotland. They are rare in most of the eastern United States and northern Rockies and common in the Pacific Northwest and prairie states. They are abundant in California, Arizona, and New Mexico, where they winter. They winter in southern California, southeastern United States, Mexico, and Guatemala, but have also been found in Michigan, New York and Connecticut during December and in Indiana during January. This suggests that some may winter farther north than was previously expected.

Sexes are generally only found together in parts of Nebraska, Montana, and the Badlands of South Dakota. Males and females are usually separated during the warmer months in North America, except during the mating season. Females appear to be more concentrated in the western part of North America. There is evidence for an altitudinal separation of sexes in California, with females concentrated in the lowlands and coastal valleys and males higher up in the foothills and mountains.

Habitat

Authorities disagree as to the bat's preference for coniferous versus broadleaf trees. Hoary bats are thought to prefer trees at the edge of clearings, but have been found in trees in heavy forests, open wooded glades, and shade trees along urban streets and in city parks.

Physical Description

The body of hoary bats is about the size of a fat mouse. Hoary bats weigh 20 to 35 g. The length from the tip of the nose to the end of the tail vertebrae is 13 to 15 cm. The wingspan is 43 cm. These bats have blunt, rounded noses and small, beady eyes. The ears are short, thick, broad, and rounded. When laid forward they do not reach the nostrils. The tragus in the ear is short and blunt. The hindfoot is half as long as the tibia and has thick fur on the dorsal side. The thumbs are long. The calcar is twice as long as the hindfoot and is narrowly keeled on the posterior edge, bearing lobes on the tip. These bats have four mammary glands.

Thick, long, soft hair covers the entire dorsal surface extending to the elbow, the median ventral border of the undersides of the wings, the ventral side of the long bones that make up the upper arm and forearm, and the basal part of the lower surface of the interfemoral tail membrane. The coloring of the dorsal area (including the tail membrane) is a mixed brown-gray with a heavy white tinge, giving these bats a frosty appearance. In fact, these bats' name means "frosty or ash colored hairy tail." The individual silky hairs are basally dark, medially yellowish, and distally black with white tips. The belly of these bats is not heavily frosted. The throat has a distinct yellow patch. The hair on the elbow, at the base of the clawed thumb, and the upper arm is yellowish as well. The ears are yellow with black edges. Brownish fur extends out on the underside of the wing nearly to the wrist.

The skull is large (16 mm long) and broad (13 mm wide), with a large auditory bullae. These bats have large, strong teeth, with the first premolar located at the inner junction of the large canine.

Juveniles appear nearly grayish, but still have a frosty appearance.

  • Range mass
    20 to 35 g
    0.70 to 1.23 oz
  • Range length
    13 to 15 cm
    5.12 to 5.91 in
  • Average wingspan
    43 cm
    16.93 in
  • Average basal metabolic rate
    1.19 cm3.O2/g/hr

Reproduction

In North America, the breeding range of hoary bats extends across Canada and northcentral and northeastern United States down to at least Kansas and Kentucky, and perhaps to Arkansas, Louisiana, and Georgia. Hoary bats are thought to mate around the time of autumn migration. Researchers are uncertain about whether copulation occurs before, during, or after the southward migration. Courtship is believed to proceed during day flights. Mating may also occur at southern wintering grounds.

Copulation is followed by delayed fertilization, a process in which the sperm is stored in the female reproductive tract all winter and is available to fertilize the egg when ovulation takes place in the spring. Parturition appears to range from the middle of May into early July. Little is known about the bat's gestation time. One study found three females to deliver between 900 and 1300 hours. Litter size is usually two, but can range from one to four.

  • Breeding interval
    Hoary bats breed once per year.
  • Breeding season
    Hoary bats breed in the autumn.
  • Range number of offspring
    1 to 4
  • Average number of offspring
    2
  • Average number of offspring
    2
    AnAge
  • Average gestation period
    56 days
  • Average gestation period
    56 days
    AnAge
  • Average weaning age
    34 days

Hoary bats give birth to their young while hanging upside down in the leafy shelter of their daytime retreat. The newborn's skin is brown, darker on the body than on the wings, and lighter beneath. The throat and head are much paler and their feet are nearly black. Fine, silver-gray hair covers their dorsal area. The hoary bat's ears and eyes are closed at birth and open on days three and twelve, respectively. Purposeful flight is possible for the infants by the thirty third day. The young cling to the mother in the day, while she sleeps, and hang on a twig or leaf while she hunts at night.

  • Parental Investment
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Behavior

Hoary bats are solitary. They roost 3 to 5 m above ground during the day, usually in the foliage of trees. They prefer dense leaf coverage above and an open area below. They also prefer trees that border clearings. They have been seen roosting in a woodpecker hole in British Columbia, in the nest of a gray squirrel, and under a driftwood plank. Occasionally they are found clinging to the overhangs of buildings and in caves in the latter part of the summer. They often have trouble finding their way out of the caves and die there.

Hoary bats reach their peak activity at about five hours after sunset, although they may occasionally be seen flying on warm winter afternoons. Their flight is stong and direct, reaching speeds of thirteen miles/hr. While hunting, they soar and glide. They forage about the tree tops, along streams and lake shores, and in urban areas where there are lots of trees. These bats stop to rest between meals at night. Feeding is the only time that hoary bats appear to associate with other bat species. Hoary bats often form groups when hunting for insects.

These bats wrap their hairy tail membrane around their curled up bodies for insulation while resting during harsh weather conditions. They become torpid when inactive during the day, as well as between feeding flights at night. When they are resting and non-torpid, they have a metabolic rate of 1.19 cc of oxygen per gram of body weight per hour.

Hoary bats can be seen flying in large groups in spring and autumn, during the time of breeding and migration. They are believed to migrate through Florida from late October to late November and from February through early May. Autumn migration occurs in waves, whereas spring migration appears to be less organized. Some hoary bats are believed to remain in the north and hibernate for the winter, rather than moving south of the United States like most do.

Communication and Perception

Like all microbats, hoary bats use echolocation while flying. They make a shrill, hissing sound when disturbed. Lasiurus cinereus is one of the only vespertilionid bats which makes an audible chatter during flight.

Food Habits

Moths (Lepidoptera) make up the bulk of the diet of hoary bats. These bats are also known to feed on flies (Diptera), beetles (Coleoptera), small wasps and their relatives (Hymenoptera), grasshoppers (Orthoptera), termites (Isoptera), and dragonflies (Odonata). The bat approaches the insect from behind, taking the abdomen and thorax in its mouth and biting off and swallowing this area of the insect, while dropping the wings and head. In comparison to other bats, hoary bats feed on relatively few orders of insects. On rare occasions, these bats have been observed to feed on leaves, grass, shed snake skin, and eastern pipistrelles.

  • Animal Foods
  • mammals
  • insects
  • Plant Foods
  • leaves

Predation

The main enemies of hoary bats are hawks and owls. American kestrels and rat snakes have on rare occasions been reported to feed on hoary bats. These bats are also known to become entangled in barbed wire fences. Another important source of mortality is females falling out of their roost with attached young, thus becoming easy prey for terrestrial passers by.

Ecosystem Roles

Hoary bats have an important ecosystem role as insect consumers. These bats are often infested with mites (Pteracarus chalinolbus and Chiroptonysus americanus), helminths (Longibucca lasiura, Oochoustica taborensis, and Physocephalus), and protozoa (Distoma).

Commensal/Parasitic Species
  • mites
  • worms
  • microorganisms
  • Pteracarus chalinolbus
  • Chiroptonysus americanus
  • Longibucca lasiura
  • Oochoustica taborensis
  • Physocephalus
  • protozoa (Distoma)

Economic Importance for Humans: Positive

Hoary bats prey on many insect species that are considered to be pests.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Hoary bats occasionally hang out under overhangs of houses and garages, but this is only menacing and they rarely cause any true disturbance to homeowners.

These bats have a relatively high incidence of rabies. In some years, 25% of sick bats collected were found to be rabid.

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

Hoary bats are widespread and secure over much of their range. One subspecies, the Hawaiian hoary bat (Lasiurus cinereus semotus), is listed as endangered by the U.S. Fish and Wildlife Service.

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Lasiurus cinereus mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Other Comments

There are three subspecies of Lasiurus cinereus: L. c. cinereus in North and Central America, L. c. semotus in Hawaii, and L. c. villosissimus in South America.

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Susan Karen Anderson (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

desert or dunes

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

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

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

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

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

nocturnal

active during the night

rainforest

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

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sexual

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

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

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

savanna

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

temperate grassland

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

urban

living in cities and large towns, landscapes dominated by human structures and activity.

viviparous

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

References

Baker, R. 1983. Michigan Mammals. Michigan State University Press. Lansing, MI. Pgs. 127-132.

Barbour, R. and W. Davis. 1969. The Bats of America. The University of Kentucky Press. Pgs. 143-148

Hoffmeister, D. 1989. Mammals of Illinois. University of Illinois Press. Urbana, Ill. Pgs. 122-125

Kurta, A. 1995. Mammals of the Great Lakes Region. The University of Michigan Press. Ann Arbor, MI. Pgs. 77-79.

Shrump, A. and K. Shrump. 23 Nov. 1982. Mammalian Species. The American Society of Mammalogists. No. 185

Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at http://www.fort.usgs.gov/WNS/.

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

Ruff, S., D. Wilson. 1999. The Smithsonian Book of North American Mammals. Washington [D.C.]: Smithsonian Institution Press in association with the American Society of Mammalogists.

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