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Indiana Bat
Myotis sodalis
Family: Vespertilionidae
Description: The Indiana bat is a medium-sized Myotis, closely resembling the little brown bay (M. lucifugus) but differing in coloration. Its fur is a dull grayfish chestnut rather than bronze, with the basal portion of the hairs of the back dull lead colored. This bat's underparts are pinkish to cinnamon, and its hind feet smaller and more delicate than in M. lucifugus. The calcar (heel of the foot) is strongly keeled.
| Status: |
Federally Listed Endangered (March 11, 1967) Global Rank: G1 State Rank: S1 |
Distribution: The Indiana bat is found primarily in the midwestern and eastern United States. The largest populations are in Arkansas, Indiana, Kentucky, Missouri, and Tennessee. Eastern Oklahoma is the western limit of its range. In Arkansas, occurrences of the Indiana bat are known from . It is thought that the Indiana bat is only a winter resident in Arkansas, moving northward in summer to Missouri and Illinois.
Habitat: The Indiana bat uses two distinct habitat types during the course of a year. Starting in August, the Indiana bat moves southward from its summer range and begins to congregate in limestone caves. Through September and October, the bats remain active and leave caves each night to forage for food and build up fat reserves for hibernation. By November, most all Indiana bats have congregated to hibernate through the winter. Limestone caves preferred for hibernation have a temperature averaging 37.9-42.9°F (3.3-6.1°C) in midwinter, and a relative humidity of 66-95%. Low cave temperatures allow the bats to maintain a low metabolic rate throughout hibernation. Only a small percentage of available caves meet the specific conditions required by Indiana bats. The hibernating bats characteristically form large, tight, compact clusters. Each individual hangs by its feet from the ceiling. Every 8 to 10 days hibernating individuals awaken to spend an hour or more flying about or to join a small cluster of active bats elsewhere in the cave before returning to hibernation.
With the onset of spring (March, April), Indiana bats begin to leave the caves and migrate northward to their summer range. During the summer, females establish maternity colonies beneath the loose bark of dead trees. Males tend to use caves during the summer. Maternity colonies and roosting individuals have also been found beneath the bark of live trees and within the cavities of dead trees. In Illinois, tree species most frequently used by maternity colonies were northern red oak (Quercus rubra), slippery elm (Ulmus rubra), cottonwood (Populus deltoides), silver maple (Acer saccharinum), and shagbark hickory (Carya ovata). Indiana bats may use the same summer roosting/maternity site repeatedly. Roost/maternity sites have a definite lifespan. As dead trees decay, useable loose bark sloughs off and eventually the entire tree will fall to the ground. Consequently, the Indiana bat is dependent upon a continual supply of dead trees.
Diet: Summer foraging by females and juveniles is limited to riparian and floodplain areas. Creeks are apparently not used if riparian trees have been removed. Males forage over floodplain ridges and hillside forests and usually roost in caves. Foraging areas average 11.2 acres (4.5 hectares) per animal in midsummer. The bulk of the Indiana bats diet appears to be Lepidoptera, with other insect groups composing a smaller proportion.
Reproduction: The Indiana bat has a definite breeding period that usually occurs during the first 10 days of October. Mating takes place at night on the ceilings of large rooms near cave entrances. Limited mating may also occur in the spring before the hibernating colonies disperse. Hibernating colonies disperse in late March and most of the bats migrate to more northern habitat for the summer. However, some males remain in the hibernating area during this period and form active bands, which wander from cave to cave.
Limited observations indicate that birth and development occur in very small, widely scattered colonies consisting of 25 or so females and their young. Birth usually takes place during June with each female bearing a single offspring. Young are born under the loose bark of dead trees in wooded stream habitats. About 25 to 37 days are required for development to the flying stage and the beginning of independent feeding.
Conservation Status: The decline of the Indiana bat is attributed to commercialization of roosting caves, wanton destruction by vandals, disturbances caused by increased numbers of spelunkers and bat banding programs, use of bats as laboratory experimental animals, and possibly insecticide poisoning. The high degree of aggregation during winter makes this species especially vulnerable to disturbance. It has been estimated that approximately 75% of the entire population hibernates in only nine caves. Disturbance during hibernation results in an increased use of stored fat reserves and, if intense or frequent enough, can result in direct or indirect mortality.
The Indiana bat is nearly extinct over most of its former range in the northeastern states, and since 1950, the major winter colonies in caves of West Virginia, Indiana, and Illinois have disappeared. Recent survey data indicates that the species has declined in abundance by 60% since the 1960s. Loss and degradation of summer habitat and roost sites due to impoundment, stream channelization, housing development, and clearcutting may be the primary factor in recent population declines.
