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Indiana Myotis

INDIANA MYOTIS

Photo Credit: Merlin D. Tuttle, Bat Conservation International

SCIENTIFIC NAME: Myotis sodalis (Miller and Allen)

OTHER NAMES: Indiana Bat, Social Myotis, Social Bat.

DESCRIPTION: A medium-sized (ave. wingspan = 24.0-26.7 cm [9.5-10.5 in.]; forearm length = 35-41 mm [1.4-1.6 in.]; weight = 6-9 g [0.2-0.3 oz.]) monotypic bat (Jordon 1986). Dorsum chestnut to dark gray, occasionally nearly black; ventral fur lighter, slate gray to cinnamon. Individual hairs strongly bicolor with dark bases and lighter tips. Fur lacking the gloss or sheen characteristic of the little brown myotis. Tragus pointed. Calcar slightly keeled. Interfermoral membrane attached to base of the toe rather than the ankle as in the gray myotis. No subspecies recognized.

DISTRIBUTION: Over much of the midwestern and eastern United States, and extending from Vermont and New Hampshire, southward to Tennessee and northern Alabama; centered in the Ohio River Valley states (Jordon 1986, USFWS 1983, 1999). Disjunct hibernating populations also have been reported from caves in the karst region of northwestern Florida (USFWS 1999). In Alabama, recently found only in the northern one-third of the state. Historical records of small hibernating groups exist from at least nine cave systems in eight counties (Jordon 1986); however, many of these records are very old and several are suspected to be misidentifications of hibernating gray myotis. Additional transients of hibernating populations also may occupy caves within the karst region of extreme south-central Alabama (Jordon 1986, USFWS 1999). The largest known hibernaculm in Alabama is located in Sauta (formerly Blowing Wind) Cave, Jackson County. Over the past 10 years (1992-2002), there have been approximately 250 Indiana myotis consistently hibernating in the same area at Sauta Cave. A substantial number also may be using Fern Cave, Jackson County (the major hibernaculm of gray myotis), but due to the incredible physical difficulty in surveying this cave, recent hibernating surveys have been lacking. In winter 2003, limited portions of Fern Cave were checked for hibernating gray and Indiana myotis. Many hundreds of thousands gray myotis were counted, but no Indiana myotis was noted. Two previously unknown hibernacula were discovered in caves in Bankhead National Forest in 1999. Indiana myotis have not been observed or collected in Alabama during the summer, with the exception of nine individuals in Bankhead National Forest, which were radio-tagged in summer 2002 while emerging from, or entering, their hibernating cave. These individuals were monitored roosting in Bankhead for several weeks until the transmitter battery failed. However, no known records of maternity sites in Alabama.

HABITAT: Complete summer habitat needs are not well understood. Early researchers considered floodplain and riparian forests to be the primary roosting and foraging habitat (Humphrey et al. 1977), whereas later research has shown upland forests are important (Clark et al. 1987).  Some evidence shows highly altered forest landscapes and disturbed areas also may be used. Caves and occasionally mines, having specific temperature, humidity, and structural characteristics are used during winter as hibernacula (USFWS 1999).

LIFE HISTORY AND ECOLOGY: During autumn, male and females migrate from their summer range to selected hibernating caves. Mating takes place prior to hibernation, with fertilization delayed until spring. Following emergence in March and April, males and females disperse to form small “bachelor” and “maternity” colonies. Males occasionally choose caves as summer roosts and, in a few instances, have remained at hibernating sites throughout the summer. Females give birth to a single offspring during early summer (June-July). Young bats are capable of flight within four weeks after birth. Maternity and bachelor colonies disperse during late summer and early autumn (August-September), with both adults and juveniles migrating to selected hibernating sites. (Harvey et al. 1998, Jordon 1986, USFWS 1999).

BASIS FOR STATUS CLASSIFICATION: Experienced substantial population declines throughout most of distribution over last 40 years. Unlike Alabama’s other endangered colonial bat, the gray myotis, whose numbers are stable or perhaps increasing, the Indiana myotis continues to decline over most of its distribution (USFWS 1999). Principal factor in decline believed to be human disturbance of hibernating bats. Once aroused, bats metabolize stored fats necessary for their survival during hibernation. Thousands of torpid M. sodalis probably have starved as a result of human disturbance during hibernation. Vandalism also has played a role in the decline. Elimination of floodplain and riparian forests also may have contributed to the decline (USFWS 1999). Listed as endangered by the U.S. Fish and Wildlife Service in 1967.

Author: M. Keith Hudson


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