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Myotis austroripariussoutheastern myotis

By Sarah Gomoll

Geographic Range

Myotis austroriparius has a disjunct distribution in the southeastern United States. It occurs locally in southeastern North Carolina, central Georgia, southern and western Alabama, western Tennessee and Arkansas, southeastern Oklahoma, and eastern Texas. It also lives along the Ohio River Valley in Kentucky, Indiana and Illinois. A large proportion of the total population is found in Florida. (Whitaker and Hamilton, 1998)

Habitat

Myotis austroriparius is predominantly a cave bat, where suitable caves occur. It will also roost in human habitations and structures such as attics, barns, bridges, and mines as well as in hollow trees or under bark. The bats are closely associated with water, as they forage ovr water when feeding at night. (Mauk-Cunningham and Jones, 1999; Whitaker and Hamilton, 1998)

  • Other Habitat Features
  • caves

Physical Description

Myotis austroriparius is a small insectivorous bat with thick, wooly fur, shorter than that found on many similar species. The fur is dark at the base and whitish at the tips. It molts in late summer, shedding a lighter coat for a darker gray. Color variation can depend on the molt, which is correlated with the reproductive status of the individual. Ammonia fumes in large caves also affect the coloring of an individual. (La Val, 1970; Whitaker and Hamilton, 1998)

The species has long been considered polytypic and has been divided into three subspecies: M. a. austroriparius, M. a. gatesi, and M. a. mumfordi. There has been research done however to show that this species should be considered monotypic. (La Val, 1970; Whitaker and Hamilton, 1998)

Total length of these bats ranges from 77 to 89 mm for males, and 80 to 97 mm for females. Forearms are between 33 and 40 mm, with males averaging slightly smaller forearms than females giving the species an average wingspread is about 238 to 270 mm. The tail is between 26 and 44 mm. Males of this species weigh between 5.1 and 6.8 g. Females weigh between 5.2 and 8.1 g. (Mauk-Cunningham and Jones, 1999)

The southeastern bat is distinguished from other myotis bats by its unusually long toe-hairs, which extend past the ends of its claws. It has a large hind foot (10 to 12 mm long). Its calcar is not keeled and its tragus is short and blunt. It has a bare, pinkish nose. It has a low sagittal crest that can be felt through the skin. (La Val, 1970; Whitaker and Hamilton, 1998)

The tooth formula in this species is: 2/3 1/1 3/3 3/3 = 38 (La Val, 1970)

  • Sexual Dimorphism
  • female larger
  • Range mass
    5.1 to 8.1 g
    0.18 to 0.29 oz
  • Range length
    77 to 97 mm
    3.03 to 3.82 in
  • Range wingspan
    270 to 238 mm
    10.63 to 9.37 in

Reproduction

As in most Myotis species, the mating system of this bat is poorly documented.

In Florida, mating is from mid-February to mid-April. Nursery colonies begin to form in mid-March. Myotis austroriparius colonies are usually between 2,000 and 90,000 individuals. These colonies tend to roost in caves that contain water. In late April to mid-May the altricial young are born. Myotis austroriparious is the only species of Myotis known to give birth to twin young. Ninety percent of females in this species produce twins (one from each uterus). Delayed fertilization does not occur in southeastern bats in Florida. There is not much known about the reproduction of the northern populations of the southeastern bat. Only a couple small maternity colonies have been found, such as one in a tree cavity in Illinois. (Sherman, 1930; Whitaker and Hamilton, 1998)

During birth, the mother forms a receptacle to catch the young. The placenta does not appear until several hours after birth, the mother pulls it out with her teeth, and proceeds to devour it. Partuition occurs generally during the day. (Sherman, 1930; Whitaker and Hamilton, 1998)

The young are born naked, with their eyes and ears closed, and weigh slightly more than 1 gram each. Baby bats are large enough to fly in 5 or 6 weeks. They grow rapidly and sexual maturity is reached in both sexes before the bats are a year old. (Sherman, 1930; Whitaker and Hamilton, 1998)

There is a high rate of pre-weaning mortality in M. austroriparius. Since southeastern bats usually roosts in caves with water, many young bats fall and drown. Even in roosting sites with no water below, a fall for a young bat usually results in death. The mortality is most severe shortly after birth. Twinning in M. austroriparius is thought to be an adaptive response to this high mortality of young. (Sherman, 1930; Whitaker and Hamilton, 1998)

  • Breeding interval
    These bats apparently breed once per year.
  • Breeding season
    Breeding occurs from February to April in Florida, although timing is probably different in the northern portion of the species' range.
  • Range number of offspring
    1 to 3
  • Range age at sexual or reproductive maturity (female)
    1 (high) years
  • Range age at sexual or reproductive maturity (male)
    1 (high) years

The parental care of M. austroriparius is not well documented. As in all mammals, the mother provides milk for her young. She also protects and grooms them. Mortality for young bats is high, as they often fall to their deaths. The role of the father in parental care in this species has not been reported. (Sherman, 1930; Whitaker and Hamilton, 1998)

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

Lifespan/Longevity

The lifespan in the wild may be no more than 4 to 8 years for most individuals, but there are records of banded individuals more than 21 years old and captives are known to have lived more than 20 years. (Nowak, 1999)

  • Range lifespan
    Status: wild
    21 (high) years
  • Range lifespan
    Status: captivity
    20 (high) years
  • Typical lifespan
    Status: wild
    4 to 8 years

Behavior

Female M. austroriparius roost in large maternal colonies (a few hundred to thousands) for part of the year. Males roost separately, either singly or in small bachelor groups. Northern populations hibernate in the winter, but Florida populations remain active. Movements between summer and winter quarters are usually local, minimally qualifying as migrations. The species often shares roosts with gray bats (Myotis grisescens), and free-tailed bats (Tadarida brasiliensis). (Whitaker and Hamilton, 1998)

Home Range

The size of the home range in this species has not been reported.

Communication and Perception

As do all Vespertilionids, or mouse-eared bats, M. austroriparius has a well-developed sense of oral echolocation. They have plain noses and their earlobes form a tragus which is used for foraging. However, this echolocation is probably not used much in communication with conspecifics. (Whitaker and Hamilton, 1998)

In communicating with conspecifics, it is likely that these bats are much like other members of the genus. They probably use audible vocal signals, as well as some tactile communication. Visual communication is probably not very important for this species. (Nowak, 1999)

Food Habits

Myotis austroriparius is an insectivorous bat that emerges after dark and feeds by flying low over the water, usually within 60 cm of the surface, and capturing prey in flight. Species from Coleoptera, Lepidoptera, and Diptera make up its diet. More specifically, it catches midges, mosquitoes, small moths, small beetles and cane flies. (Whitaker and Hamilton, 1998)

  • Animal Foods
  • insects

Predation

The most common predators of southeastern bats appear to be rat snakes and corn snakes, which are common in caves. Other enemies also include climbing mammals, such as opossums, and some species of owls. Large cockroaches can prey on newborns that fall to the ground. Some ectoparasites such as the streblid fly (Trichobius major), the nycteribiid fly (Basilia boardmani) and chiggers (Euschoengastia pipistrelli) have been found on M. austroriparius. (Whitaker and Hamilton, 1998)

Ecosystem Roles

Similar to other insectivorous animals, southeastern bats play an important ecosystem role in controlling insect populations. (Whitaker and Hamilton, 1998)

Economic Importance for Humans: Positive

Just like other insectivores, this bat is highly beneficial to humans because they feed on a variety of nocturnal insects such as mosquitoes. (Whitaker and Hamilton, 1998)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Like other members of the genus, M. austroriparius can come into conflict with humans by occupying buildings. It is also a common concern that bats can spread rabies, but incidence of rabies in bats is quite low. There is currently no evidence of M. austroriparius being involved in the transmission of any particular case of rabies, so human concerns about this species as a vector of the disease are more theorhetical than pratical. (Whitaker and Hamilton, 1998)

Conservation Status

The U.S. Fish and Wildlife Service currently list southeastern bats as a Species of Concern. The population of these animals has declined across much of its range for several reasons. Alteration of their critical cave habitat is the most likely cause. The closing off of their entrances, flooding by dams, vandalism and campfires, has altered caves. Clear cutting of forest surrounding the caves is also known to affect southeastern bats. Hibernating bats can be awakened by excessive human visitation, causing the bats to use important fat reserves. If maternal colonies are disturbed, female bats may abandon young. Populations of up to 250,000 individuals have been documented in caves in northern Florida and the species appears to be rare in the rest of its range. This apparent rarity could be an artifact of lack of knowledge about the species and its locations. Enforcement of cave protection is often difficult and impractical but Florida's maternity caves urgently need protection. (Gore and Hovis, 1992)

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

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Sarah Gomoll (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor, instructor), University of Wisconsin-Stevens Point.

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

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

echolocation

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

endothermic

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

fertilization

union of egg and spermatozoan

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

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).

ultrasound

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

visual

uses sight to communicate

viviparous

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

References

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/.

Gore, J., J. Hovis. 1992. The Southeastern Bat: Another Cave-roosting Species in Peril. Bats, Summer: 10-12.

Hermanson, J., K. Wilkins. 1986. Pre-weaning mortality in a Florida maternity roost of Myotis austroriparius and Tadarida brasiliensis . Journal of Mammalogy, 67: 751-754.

La Val, R. 1970. Infraspecific relationships of bats of the species Myotis austroriparius . Journal of Mammalogy, 51: 542-552.

Mauk-Cunningham, C., C. Jones. 1999. Southeastern myotis (Myotis austroriparius). Pp. 83-85 in D Wilson, S Ruff, eds. The Smithsonian Book of North American Mammals. Washington, D.C. and London: The Smithsonian Insitution Press.

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

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.

Sherman, H. 1930. Birth of the young of Myotis austroriparius . Journal of Mammalogy, 11: 495-503.

Whitaker, J., W. Hamilton. 1998. Mammals of the Eastern United States. Ithaca, New York: Cornell University Press.

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