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Lasionycteris noctivaganssilver-haired bat

By Robert Naumann

Geographic Range

Silver-haired bats are found throughout the United States (with Florida as a possible exception), northward into southern Canada up to the treeline, and reach their northern limits in Alaska . The range may also include extreme northeastern Mexico (due to similar habitat conditions), although there have been no confirmed sightings of the bat.

Habitat

Silver-haired bats prefer temperate, northern hardwoods with ponds or streams nearby. The typical day roost for the bat is behind loose tree bark. Silver-haired bats appear to be particularly fond of willow, maple and ash trees (most likely due to the deeply fissured bark). Hollow snags and bird nests also provide daytime roosting areas for silver-haired bats. Less common daytime roosts include buildings, such as open sheds and garages; however, due to their solitary nature and adaptation to woodland roosts, these bats rarely invade buildings in large enough numbers to cause alarm. During the winter months, silver-haired bats that hibernate find shelter in northern areas inside trees, buildings, rock crevices, and similar protected structures.

Physical Description

Silver-haired bats are medium sized bats, weighing 8 to 12 grams. Measurements of these bats include: total length, 90 to 115 mm; tail length, 35 to 50 mm; wingspread, 270 to 310 mm; forearm, 37 to 44 mm; head size, 60 mm long; and a hind foot length of 6 to 12 mm. Silver-haired bats receive their name from their dark, silver-tipped fur. The fur is usually black in color, however some individuals may be dark brown with yellow-tipped fur. The ears of these bats are relatively short (15 to 17 mm in height), round, and naked. The dorsal surface of the interfemoral membrane is lightly furred, with 50 to 75% of the tail being naked.

  • Range mass
    8 to 12 g
    0.28 to 0.42 oz
  • Range length
    90 to 115 mm
    3.54 to 4.53 in
  • Range wingspan
    270 to 310 mm
    10.63 to 12.20 in

Reproduction

Courtship and mating of silver-haired bats occurs in autumn when both sexes congregate for migration. Fertilization is delayed until the next spring. Births occur after a gestation period of 50 to 60 days. At parturition, the female roosts with her head facing upward. The tail membrane is bent forward to form a basket, in which the young are caught as they leave the birth canal. Two young are produced, usually between late June and early July.

  • Breeding season
    Courtship and mating of silver-haired bats occurs in autumn.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    2
  • Average number of offspring
    2
    AnAge
  • Range gestation period
    50 to 60 days
  • Average birth mass
    1.67 g
    0.06 oz
    AnAge
  • Average weaning age
    36 days
  • Range time to independence
    21 to 36 days
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    152 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    152 days
    AnAge

Newborns weigh about 2g. The litter weight equals 36% of the mother's body weight. Young are born with their eyes closed, ears folded over, and most of their 22 deciduous teeth in place. Within a period of 21 to 36 days, young are able to forage for themselves.

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

Lifespan / Longevity

Tooth wear of silver-haired bats suggests that these bats can live up to 12 years.

  • Typical lifespan
    Status: wild
    12 (high) years
  • Average lifespan
    Status: wild
    12 years

Behavior

Silver-haired bats have been reported to be one of the earliest fliers in the evening, sometimes appearing in broad daylight. However, other sources claim that these bats are late-evening fliers. The flying time of silver-haired bats is believed to be adjusted by the bat so that it will not conflict with the flying times of the red, hoary, or big brown bats. Silver haired-bats are believed to be one of the slowest flying bats in North America (possibly second to western pipestrelles), with a flight speed of 4.8-5.0 m/s.

The adults usually appear singly, but can occasionally be found in pairs or small groups. During the summer, the bats are believed to segregate by sex. During late summer and autumn, however, silver-haired bats join in groups containing both sexes to migrate to the southern parts of their range. Some silver-haired bats are also known to hibernate in the northern locations.

Communication and Perception

Silver-haired bats use echolocation to find their prey. They have acute hearing, and communicate with one another using sound. Baby bats give high-pitched chirps when they become separated from their mothers.

Food Habits

Silver-haired bats are insectivorous. Their diet mainly consists of flies, beetles, and moths. However, these bats feed opportunistically on any concentration of insects they come across. They have a short-range foraging strategy, traveling over woodland ponds and streams. Silver-haired bats do not always feed in mid-flight; they have been caught in mouse traps, suggesting ground foraging, and they have been reported to consume larvae on trees.

  • Animal Foods
  • insects

Predation

Predators of silver-haired bats include striped skunks and great horned owls.

Ecosystem Roles

Silver-haired bats have an important role in the food chain as consumers of vast quantities of insects.

Economic Importance for Humans

Economic Importance for Humans: Positive

Silver-haired bats help with insect control, consuming large numbers of insects each night.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Silver-haired bats are occasionally implicated in the transmission of rabies to humans.

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

Silver-haired bats have no special endangered or threatened status; however, activities such as logging and deforestation may pose a threat for the bat in the future.

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 Lasionycteris noctivagans 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

Fisherman occasionally snag silver-haired bats in mid-air while casting their fishing lines.

Contributors

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

Robert Naumann (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

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

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.

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

seasonal breeding

breeding is confined to a particular season

sexual

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

social

associates with others of its species; forms social groups.

solitary

lives alone

sperm-storing

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

tactile

uses touch to communicate

temperate

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

viviparous

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

References

Baker, Rollin H. 1983. Michigan Mammals. Michigan State University Press.

Barbour, Roger W. and Wayne H. Davis. 1969. Bats of America. The University Press of Kentucky

Barclay, Robert M. 1986. Long-versus Short-range Foraging Strategies of Hoary (Lasiurus cinerus) and Silver-haired (Lasionycteris noctivagans) Bats and the Consequences for Prey Selection. Canadian Journal of Zoology. 63: 2507-15.

Barclay, Robert M., Paul A. Faure, and David R. Farr. 1988. Roosting Behavior and Roost Selection by Migrating Silver-haired Bats (Lasionycteris noctivagans). Journal of Mammology. 69: (4) 821-825.

Kurta, Allen. 1995. Mammals of the Great Lakes Region. The University of Michigan Press.

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.

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