Myotis austroriparius

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.

• Biogeographic Regions
• nearctic nearctic
  • native native

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.

• Habitat Regions
• temperate temperate

• 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.

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.

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.

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.

The tooth formula in this species is: 2/3 1/1 3/3 3/3 = 38

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

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.

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.

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.

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

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.

• Parental Investment
• no parental involvement
• altricial 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.

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 ).

• Key Behaviors
• flies
• nocturnal nocturnal
• motile motile
• migratory migratory
• hibernation hibernation
• colonial colonial

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.

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.

• Communication Channels
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• ultrasound ultrasound
• echolocation echolocation
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• 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 .

Ecosystem Roles

Similar to other insectivorous animals, southeastern bats play an important ecosystem role in controlling insect populations.

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.

• 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.

• Negative Impacts
• injures humans
  • carries human disease
• causes or carries domestic animal disease causes or carries domestic animal disease
• household pest

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.

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.

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

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

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 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.