Myotis sodalis - Indiana Bat

Physical Description:

The Indiana bat, Myotis sodalis, is a small bat with a weight that ranges from approximately 5 to 11 grams.  The forearm ranges from approximately 36 to 40.4mm, the hind foot from approximately 8 to 10mm, the tail length from approximately 27 to 44mm, and the ear height from approximately 12 to 15mm.  The total length ranges from approximately 70 to 100mm.  This bat is covered in dark brownish-black fur, and has dark colored ears, patagium, and uropatagium.  There are small transparent hairs on both the upper and lower side of the patagium.  These hairs assist with flight as well as the capture of their prey.  The Indiana bat has hind legs that are bent at 180 degrees to allow them to hang upside-down against a flat surface.  Sodalis is easily confused with other bats in the genus Myotis, more so with the little brown bat (Myotis lucifugus).  A common distinguishing characteristic is the length of the hairs on their toes.  Myotis sodalis has hairs that don’t grow past the claw like the hairs of lucifugus.  (Hoffmeister, 1989, Jones, 1966, Wilson, 1997).

Distribution:

The Indiana bat’s geographic range covers the central and eastern states of the United States.  They are most common in Illinois, Indiana, Tennessee, West Virginia, Ohio, Kentucky, and Pennsylvania.  This bat is also found in parts of Mississippi, Arkansas, Georgia, Iowa, New York, Vermont, New Hampshire, and Massachusetts.  Other states where sightings have been reported include South Carolina, North Carolina, Maryland, Connecticut, Virginia, Michigan, and Wisconsin.  Only one individual has been recorded in Wisconsin.  This data was collected in Grant County of South-western Wisconsin in an old mine (Jackson, 1961).  In the summer the geographic range increases for roosting and feeding purposes.  It is likely that this individual may have been misidentified due to the lack of species available.  During the winter, the range greatly decreases due to the limited space available for hibernacula.  (Kurta, 1995).

Indiana Bat (Myotis sodalis) habitat range

Indiana Bat (Myotis sodalis) habitat range

© Bat Conservation International, Inc., 2002.

http://www.batcon.org/discover/species/mysodal.html

Ontogeny and Reproduction:

The Indiana bat copulates prior to hibernation and uses a method called delayed fertilization.  The sperm is stored during the winter inside the cooled body of the female, and when spring comes and the bats leave their hibernacula, the female has the ability to control whether or not fertilization will occur.  Her physical condition and resource availability determines her actions.  This behavior can increase her chances for survival by not jeopardizing either her young or herself.  Delayed fertilization is used also as a benefit to the males.  After a long hibernation the males lack the physical fitness to mate during the spring when they are just waking up from the winter.  Fertilization generally occurs sometime in April and the gestation period is around 60 days and usually results in a single pup once every year.  Mothers will give birth in maternity roosts with other Indiana bats under the peeling or loose bark of some trees.  Here, the young will mature for approximately a month before they attempt to fly and feed on their own.  The life span of the Indiana bat is approximately 14 years.  (Kurta, 1995, Menzel et. al, 2001).

Ecology:

The Indiana bat occupies the central and eastern parts of the United States.  During the summer 80% of this bat population will occupy trees of various species in forested areas.  Green ash, red oak, shagbark, hickory, American elm, and cottonwood trees are commonly used.  Other bats utilize different resources such as trees in less forested areas, bat houses, and other human built structures such as attics and poles.  Generally, all roosts are near some sort of water source.  During the fall this bat will migrate to a hibernacula.  85% of this population of Indiana bats hibernates in only 7 caves; two of these contain over half of this population.  This indicates that the criteria for Indiana bat hibernacula are very limited.  These hibernacula are generally limestone caves and old mine tunnels located in the central eastern part of the U.S.; mainly Tennessee and Kentucky.  The airflow tends to be noticeable but not excessive or absent with the humidity somewhere around 70% to 100%.  A large opening and high ceilings with winter temperatures at the lowest non-freezing point possible are preferred.  These temperatures hover around the 2 to 5 degree C point.  (Menzel et. al, 2001, Tuttle, 1988, Allen, 1939).

Behavior:

The Indiana bat (Myotis sodalis) uses flight as their main mode of locomotion.  Bats, in general, are the only mammals that possess true flight.  This bat is an echo locating bat, which means that they use their flight and a complex sonar system to capture their prey.  Sodalis are strictly insectivorous consuming both soft and hard bodied insects.  After hibernation, their diet consists of mostly butterflies and moths with some flies.  Females going through lactation will tend to consume more moths than others due to the increased nutrition level.  Beetles are occasionally preyed upon, though much less often.  In one night this bat will consume up to half of its weight in insects.  Males are more likely to prey over trees in a denser forest, whereas females and the young prey over flood plains and streamside trees.

        Following a long hibernation period, the hungry Indiana bat disperses into many plentiful regions for the summer, one of which is the Great Lakes region around late April.  Upon dispersal, fertilization will occur and the females will then gather in maternity roosts to give birth and raise their young.  Males will roost in a variety of places and group sizes.  The females will form clumps in various trees that number from around 4 to 45 or more, and tend to return to the same general roost location every year.  These roosts are separated into two categories, the first being the primary roost where there are clumps of more than 30 bats.  Usually these roosts won’t exceed 100 bats.  The second is the alternate roost where these bat clumps locations are much less populated.  Once at the roost, the female will burrow in the bark of a tree.  The tree must have dying or loose bark on it for the bat to roost.  After about a month the young are able to fly, and around mid August into September and October, the migration back to their hibernacula takes place.

        Upon arrival, there is a burst in the consumption of food to increase their fat stores for the months of inactivity ahead.  On average the bats weight will increase with females then being approximately 8.9 grams and males being approximately 8 grams.  Copulation takes place as well at this time.  Generally it is the females that will enter into the hibernacula first and then the males.  The males enter later because this allows them to copulate with more females entering the cave, increasing their chances of fathering young.  Once established in their hibernacula, all bat activity ceases and they hang from the cave ceiling for approximately 190 days (5 to 6 months).  Initially their weight loss is about 0.016 grams per day and eventually slows to 0.008 grams per day during the middle of winter.  These bats have the ability to lower their body temperature and therefore decrease their metabolic rate slowing the rate at which fat stores are being burned.  These bats do, however, awake every 8 to 10 days but major movement is not exhibited.  Clumps of these hibernating bats can reach up to 100,000 individuals, making body temperature regulation much less energy expensive for each individual.  For this reason, clump size will tend to be larger in the cooler hibernacula than in the warmer ones.  Higher temperatures tend to promote higher metabolic rates that can result in the early depletion of the energy reserves of a bat.  (Kurta et al, 1998, Tuttle, 1988, U.S. Fish and Wildlife Service Division of Endangered Species, 1999, Wilson, 1997).

Remarks:

    Positive economic importance:

        The Indiana bat consumes many insects that are considered harmful to people either physically, as mosquitoes and some flies are, or economically as moths and other insectivorous pests are.  Bats in general are an important part of any ecosystem and to eliminate them would most likely result in a dramatic increase in insect populations and consequently the damage caused by them.  In addition to naturally managing the insect populations, the Indiana bat is a good indicator of environmental health, given that this bat is sensitive to pesticides and pollution.  Another economic value of the Indiana bat is from the use of their Guano, or waste, which can be harvested for further use in cosmetics and as fertilizer.  (Linzey, 2002, National Wildlife Federation, 2003).

    Negative economic importance:

        The Indiana bat, just like any other bat, is susceptible to rabies and histoplasmosis, a disease contracted by breathing in dust that contains contaminated spores.  Though diseases contracted by bats are rare there still is a slight chance and not much reason for worry.  A bat infected with rabies is not aggressive and will not attack or retaliate unless probed or touched in any way.  Less than half of 1% of bats carries rabies but it is still not a good idea to carelessly handle any bat.  (Linzey, 2002, National Wildlife Federation, 2003).

Recent Conservation:

Currently the Indiana bat is listed as endangered by the U.S. DNR and therefore is federally protected.  This bat is a keystone species within its ecosystem and is very sensitive to human activities such as pesticide use, deforestation and other habitat destruction, as well as tourism.  Other events can alter the lives of this bat too, such as extended winters, short summers, storms, etc.  When interacting with this bat or its ecosystem, humans must be very careful not to disturb them.  At this time the Indiana bat hibernacula disturbance is strictly monitored and disturbance is kept to a minimum.  Currently there are two caves that are listed as critical habitat.  One is White oak blowhole cave in Tennessee and the other is Bat cave in Kentucky.  (National Wildlife Federation, 2003).

Literature Cited:

Allen, G.M.  1939.  Bats.  Dover Publications, Inc.

Hoffmeister, D.F.  1989.  Mammals of Illinois: 98-99.

Jackson, H.H.T.  1961.  Mammals of Wisconsin:83-84.  University of Wisconsin Press.

Jones, J.K.  1966.  The Distributional Status of Bats in Kansas.  Robert R. Sanders, State Printer Topeka, Kansas.

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

Kurta, A., J.O. Whitaker, jr.  1998.  Diet of the Endangered Indiana Bat (Myotis sodalis) on the Edge of its Range.  The American Midland Naturalist 140: 280-286.

Linzey, D. and C. Brecht.  2002.  <www.discoverlife.org/nh/tx/Vertebrata/Mammalia/Vespertilionidae/Myotis/sodalis/>.

Menzel, M.A., et. Al.  2001.  Review of the Forest Habitat: Relationships of the Indiana Bat (Myotis sodalis).  USDA Forest Service Northeastern Research Station.

National Wildlife Federation.  2003.  <www.nwf.org/keepthewildalive/bat/bigpicture.cfm>.

Tuttle, M.D.  1988.  America’s Neighborhood Bats.  University of Texas Press, Austin.

U.S. Fish and Wildlife Service.  1999.  <http://endangered.fws.gov/i/a08.html>.

U.S. Fish and Wildlife Service Division of Endangered Species.  1991.  <http://endangered.fws.gov/i/a/saa08.html>.

_____.  1999.  <http://nc-es.fws.gov/mammal/IndBatBioSheet.pdf>.

Wilson, D.E.  1997.  Bats in Question: The Smithsonian Answer Book.  Smithsonian Institutional Press.

 
Reference written by Erin Iberg, Biol 378: Edited by Chris Yahnke. Page last updated 4-28-04.