Indiana bat (Myotis sodalis)

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Indiana bat on cave wall
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Indiana bat fact file

Indiana bat description

KingdomAnimalia
PhylumChordata
ClassMammalia
OrderChiroptera
FamilyVespertilionidae
GenusMyotis (1)

This small bat weighs the same as about three pennies, but is not the smallest of the 87 Myotis species. Myotis means ‘mouse ear’ and refers to the relatively small, mouse-like ears of these bats. This species gets the name ‘sodalis’, meaning ‘companion’, from its social behaviour (3). The Indiana bat has fine and fluffy fur that is dull greyish-chestnut with a black basal portion on the upperparts, whilst the underparts are pinkish to cinnamon (2). Several characteristics distinguish the Indiana bat from similar species; the light pink nose, small, delicate hind feet with sparse, short hairs that do not extend beyond the toes, and a calcar (the spur extending from the ankle) that has a slight keel (4). In addition, the ears and wing membranes have a dull appearance, and the fur is less glossy than that of the similar little brown bat (Myotis lucifugus) (3).

Also known as
social bat.
Size
Head-body length: 41 – 49 mm (2)
Tail length: 27 – 44 mm (2)
Wingspan: 240 – 267 mm (2)
Weight
5 – 11 g (2)
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Indiana bat biology

The Indiana bat is a migratory species that hibernates colonially during the winter. In late summer or early autumn they gather at their hibernating sites, or hibernacula, where they mate. The bats then cluster tightly together in groups of up to 5,000, hanging from the ceiling of the cave or mine, and enter hibernation (2). Whilst they mate in autumn, females do not fall pregnant until after they emerge from the caves in spring. This is achieved by the female storing the male’s sperm over winter and then ovulating in spring, allowing fertilization to occur (2) (3). After hibernation, the females are the first to migrate to wooded areas, whilst males and non-reproductive females may migrate later on, or remain near the hibernaculum (3). Migration to the summer habitat can involve travelling great distances of up to 575 kilometres. Groups of around 100 females gather together in the summer habitat, forming maternity colonies (3). Here, each female gives birth to only one young, which are able to fly within one month after birth, but stay with the maternity colony throughout their first summer (3) (4).

The Indiana bat is insectivorous, meaning it feeds only on insects. They can consume up to half their body weight in insects each night, and thus their role in controlling insect populations is a significant one (3). Bats also play an essential role in cave ecosystems by bringing in nutrients in the form of guano upon which many forms of life depend (6).

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Indiana bat range

Occurs in the Midwest and eastern United States; from Oklahoma and Iowa, north and east to Michigan, New York and Vermont, and south to Alabama and Arkansas In summer it is apparently absent south of Tennessee; in winter it is apparently absent from Michigan, Ohio, and northern Indiana (2) (5).

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Indiana bat habitat

During winter, Indiana bats hibernate in limestone caves, or occasionally abandoned mines. They have quite specific habitat requirements, preferring cool, humid caves with stable temperatures averaging two to seven degrees Celsius. In summer the Indiana bat can be found in wooded areas, where they usually roost under loose tree bark on dead or dying trees, or under bridges and in old buildings (3). They forage along river and lake shorelines, in the tree tops in floodplains and in upland forest (2).

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Indiana bat status

Classified as Endangered (EN) on the IUCN Red List 2007 (1).

IUCN Red List species status – Endangered

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Indiana bat threats

Recently, the Indiana bat has been suffering from a decline in numbers due to a range of threats. During hibernation, the Indiana bat is vulnerable to human disturbance, which can cause direct mortality, or cause them to rouse and deplete their important energy reserves. Disturbance can be in the form of researchers, vandalism, and the commercialization of caves, allowing tourists to visit caves. Modifications to mines and caves, such as the construction of gates to restrict human access, alter airflow, temperature and humidity, to which the Indiana bat is very sensitive; or gates may not allow sufficient flight space for the bats and thus block them from a critical hibernation site (2) (3). As Indiana bats hibernate in very large numbers in only a few caves, this makes them particularly vulnerable to disturbance and natural disasters, as a large proportion of the total population can be affected by a single event (3).

The summer habitat is also threatened by habitat loss and degradation, caused by housing development, clear-cutting for agriculture, or forest management practices that result in a shortage of suitable roosting sites for breeding females (2). The use of pesticides is also likely to have affected the Indiana bat by reducing insect populations on which they depend (4)

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Indiana bat conservation

As well as being classified as Endangered on the IUCN Red List 2007 (1), the Indiana bat is also listed as Endangered under the Endangered Species Act of 1973. As an outcome of this, the U.S. Fish and Wildlife Service has drawn up a recovery plan, with the goal of improving the status of the Indiana bat so that it can be removed from the Endangered Species List (3). To reach the goal a number of actions are required; conserving and managing the hibernacula and the summer habitat, conducting further essential research, and implementing a public information and outreach program. Dependent on funding and the implementation of conservation actions, it has been estimated that the species can fully recover by the year 2027 (3). At present, the primary conservation effort has been to control human access of caves by erecting properly designed gates that keep people from disturbing hibernating bats while maintaining temperature, humidity and allowing access for bats (3).

View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

For further information on the Indiana bat see:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
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Glossary

Colonial
Relating to or belonging to a colony (a group of organisms living together in a group).
Colony
A group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds.
Foraging
The act of searching for food.
Guano
Accumulated droppings found where large colonies of animals such as seals, bats or birds occur; it is rich in plant nutrients.
Hibernate
Hibernation is a winter survival strategy characteristic of some mammals in which an animal’s metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer.
Keel
A projecting ridge along a flat or curved surface, particularly down the middle.
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References

  1. IUCN Red List (June, 2008)
    http://www.iucnredlist.org
  2. NatureServe. (June, 2007)
    http://www.natureserve.org/explorer
  3. US Fish and Wildlife Service. (2007) Indiana Bat (Myotis sodalis) Draft Recovery Plan: First Revision. U.S. Fish and Wildlife Service, Fort Snelling. Available at:
    http://ecos.fws.gov/tess_public/SpeciesRecovery.do?sort=1
  4. Kentucky Bat Working Group (June, 2007)
    http://www.biology.eku.edu/bats/indianabat.htm
  5. U.S. Fish and Wildlife Service (June, 2008)
    http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=A000
  6. LaRoe, E.T., Farris, G.S., Puckett, C.E., Doran, P.D. and Mac, M.J. (1995) Our Living Resources: a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. U.S. Department of the Interior, National Biological Service, Washington, DC.
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Image credit

Indiana bat on cave wall  
Indiana bat on cave wall

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