|Scientific Name:||Myotis sodalis|
|Species Authority:||Miller & Allen, 1928|
|Red List Category & Criteria:||Endangered A2ac ver 3.1|
|Assessor(s):||Arroyo-Cabrales, J. & Álvarez-Castañeda, S.T.|
|Reviewer(s):||Medellín, R. & Schipper, J.|
Listed as Endangered because of a serious population decline, estimated to be more than 50% over the 10 years, based on direct observation and a decline on its extent of occurrence.
|Range Description:||The range extends west to the western Ozark region in eastern Oklahoma (Saugey et al. 1990) and Iowa (Clark et al. 1987), north and east to Michigan (Evers 1992, Kurta and Teramino 1994, Kurta 1995), New York, New England, and northern New Jersey, and south to northern Alabama and Arkansas, with accidental/non regular occurrences outside this range. The species has disappeared from or greatly declined in most of its former range in the northeastern United States (e.g., Trombulak et al. 2001). A disjunct population once existed in northwestern Florida, though old Florida records may represent accidental occurrences.
Most known maternity sites have been located in forested tracts in agriculturally dominated landscapes (e.g., Missouri, Iowa, Indiana, Illinois) (U.S. Fish and Wildlife Service 1999), but maternity colonies also exist to the south in heavily forested regions to at least eastern Tennessee and western North Carolina (Britzke et al. 2003). In summer these bats are apparently absent south of Tennessee. There is a July 1993 record for South Carolina (South Carolina Heritage Trust), but this record may lack adequate documentation; Menzel et al. (2003) did not report any records for the state.
Northern populations migrate south to Alabama, Tennessee, Kentucky, Indiana, Missouri, and West Virginia for winter. In winter, they are apparently absent from Michigan, Ohio, and northern Indiana where suitable caves and mines are unknown. The most important hibernating caves are: Bat Wing and Twin Domes caves (Indiana); Bat, Hundred Dome, and Dixon caves (Kentucky); and Bat Cave, Great Scott Cave, and Pilot Knob Mine (Missouri); Pilot Knob Mine is the largest colony (Lowe 1990). Half of the total population hibernates in southern Indiana.
|Range Map:||Click here to open the map viewer and explore range.|
Total known population at major hibernacula was about 883,720 in 1960/1970, 679,170 around 1980, 473,970 around 1990, and 387,300 in 2003 (Clawson 2004). Census data from 1995-1997 indicate an abundance decline of about 60 percent since population surveys began in the 1960s; the most severe declines have occurred in Kentucky and Missouri, where the decline totals 430,000 individuals over the past few decades (Federal Register, 9 April 1999). In Indiana, bat numbers in 2001 appeared to be stable to slightly increasing. In Kentucky, their numbers appeared to be declining, but not so rapidly as in Missouri, where between 1975 and 1995, the number of Indiana bats at major hibernating sites declined from more than 120,000 to nearly 20,000 (USFWS 2001).
Since 195O, the major winter colonies in caves in West Virginia, Indiana, and Illinois have disappeared. Wintering populations in Vermont have declined dramatically since the 1930s (Trombulak et al. 2001). The overall population at major roosts declined about 56% between 1960/1970 and 2003 (Clawson 2004). Hibernating populations in the southern part of the range have declined by 82% in the past 40 years, while those in the northern Midwest and Northeast have increased by 35% (Clawson 2004).
|Habitat and Ecology:||
This species is represented by many maternity occurrences and hibernacula, but the majority of the population hibernates at relatively few sites, including several caves and one mine in Missouri, southern Indiana, and Kentucky (Brady et al. 1983, USFWS 1999). About 85% of the total population hibernates in nine Priority 1 caves, which contain at least 30,000 bats; the remaining 15 percent of the population have been or currently are distributed among 50+ Priority II and III hibernacula (Menzel et al. 2001). About ninety wintering sites are known.
Maternity colonies consist of small, widely scattered colonies of females (rarely more than 100) and their young. These are more widely distributed and numerous than are major hibernacula. For example, individuals from one hibernaculum in New York used many roost trees (Britzke et al. 2006). Captures of reproductively active females or juveniles at 24 sites in 16 counties in Illinois indicate that maternity colonies of this species occur throughout the range of this species in that state (Gardner et al. 1996). Maternity sites have been found in 13 counties in Kentucky (Kentucky Bat Working Group; http://www.biology.eku.edu/bats/indianabat.htm).
Myotis sodalis hibernates in caves; maternity sites generally are behind loose bark of dead or dying trees or in tree cavities (Menzel et al. 2001). Foraging habitats riparian areas, upland forests, ponds, and fields (Menzel et al. 2001), but forested landscapes are the most important habitat in agricultural landscapes (Menzel et al. 2005).
In hibernation, limestone caves with pools are preferred. Hall (1962) noted that preferred caves are of medium size with large, shallow passageways. Roosts usually are in the coldest part of the cave. Preferred sites have a mean midwinter air temperature of 4-8 C (tolerates much broader range) (Hall 1962, Henshaw and Folk 1966), well below that of caves that are not chosen (Clawson et al. 1980). Roost sites within caves may shift such that bats remain in the coldest area (Clawson et al. 1980); individuals may move from a location deeper in the cave to a site nearer the entrance as the cold season progresses; they may move away from areas that go below freezing. Hibernation in the coldest parts of the cave ensures a sufficiently low metabolic rate so that the fat reserves last through the six-month hibernation period (Henshaw and Folk 1966, Humphrey 1978). Relative humidity in occupied caves ranges from 66 to 95% and averages 87% throughout the year (Barbour and Davis 1969, Clawson et al. 1980). Because of these requirements, M. sodalis is highly selective of hibernacula.
During the fall, when these bats swarm and mate at their hibernacula, males roost in trees nearby during the day and fly to the cave during the night. In Kentucky, Kiser and Elliott (1996) found males roosting primarily in dead trees on upper slopes and ridgetops within 2.4 km of their hibernaculum. During September in West Virginia, males roosted within 5.6 km in trees near ridgetops, and often switched roost trees from day to day (C. Stihler, West Virginia Division of Natural Resources, pers. observ., October 1996, cited in USFWS 1999). Fall roost trees tend to be in sunnier areas rather than being shaded (J. MacGregor, pers. observ., October 1996, cited in USFWS 1999). In summer, habitat consists of wooded or semiwooded areas, often but not always along streams. Solitary females or small maternity colonies bear their offspring in hollow trees or under loose bark of living or dead trees (Humphrey et al. 1977, Garner and Gardner 1992). Humphrey et al. (1977) determined that dead trees are preferred roost sites and that trees standing in sunny openings are attractive because the air spaces and crevices under the bark are warmer. In Illinois, Garner and Gardner (1992) found that typical roosts were beneath the exfoliating bark of dead trees; other roost sites were beneath the bark of living trees and in cavities of dead trees. Kurta et al. (1993) found a large maternity colony in a dead, hollow, barkless, unshaded sycamore tree in a pasture in Illinois. In Michigan, a reproductively active colony occupied eight different roost trees (all green ash), all of which were exposed to direct sunlight throughout the day; bats roosted beneath loose bark of dead trees (Kurta et al. 1993). In western Virginia, a male used a mature, live, shagbark hickry tree as a diurnal roost; the bat foraged primarily among tree canopies of an 80-year-old oak-hickory forest (Hobson and Holland 1995). In Missouri, primary maternity roosts were in standing dead trees exposed to direct sunlight; there were 1-3 primary roosts per colony; alternate roosts were in living and dead trees that typically were within the shaded forest interior (Callahan et al. 1997). See Garner and Garner (1992) for detailed information on summer habitat in Illinois. Though maternity sites have been reported as occurring mainly in riparian and floodplain forests (Humphrey et al. 1977, Garner and Gardner 1992), recent studies indicate that upland habitats are used by maternity colonies much more extensively than previously reported. Garner and Gardner (1992) reported that 38 of 51 roost trees in Illinois occurred in uplands and 13 trees were in floodplains. Of the 47 trees in forested habitat, 27 were in areas having a closed (80-100%) canopy, and 15 were in areas having an intermediate (30-80%) canopy. A single roost tree was found in the following types of habitat: a heavily grazed ridgetop pasture with a few scattered dead trees, a partially wooded swine feedlot, a palustrine wetland with emergent vegetation, a forested island in the Mississippi river, and a clearcut around a segment of an intermittent stream where dead trees were retained for wildlife. Roosts were not found in forests with open canopies (10-30%) or in old fields with less than or equal to 10% canopy cover. In eastern Tennessee and western North Carolina, several maternity colonies were in sun-exposed conifer snags (roost sites were above the surrounding canopy); some of these snags fell and were not used in subsequent years (Britzke et al. 2003). Rarely maternity colonies have been found in crevices in utility poles or in bat boxes (e.g., Ritzi et al. 2005). See Menzel et al. (2001) for a review of forest habitat relationships. Known roost tree species include elm, oak, beech, hickory, maple, ash, sassafras, birch, sycamore, locust, aspen, cottonwood, pine, and hemlock (Cope et al. 1974, Humphrey et al. 1977, Garner and Gardner 1992, Britzke et al. 2003, Britzke et al. 2006), especially trees with exfoliating bark.
In Illinois, Indiana bats used the same, evidently traditional, roost sites in successive summers. Recapture of the same individuals within traditional roost sites during subsequent summers suggests site fidelity (Garner and Gardner 1992, Gardner et al. 1996). Relatively few individuals roost in caves at the mouths of which late summer swarming occurs (Cope and Humphrey 1977, Barbour and Davis 1969).
|Major Threat(s):||A significant threat is human disturbance at winter caves, which causes aroused bats to deplete energy reserves (Mohr 1972, Engel et al. 1976). Handling of hibernating bats by researchers may result in the bats moving to the use of less suitable hibernacula, causing additional loss of fat reserves (Jones 1971 in Engel et al. 1976). In southern Indiana, Johnson et al. (1998) found that populations subject to high human visitation experienced increased weight loss in winter, but populations in each of two disturbed hibernacula increased in abundance, suggesting that "M. sodalis is affected by limiting factors other than, or in addition to, human visitation in winter." Vandalism and indiscriminate killing have been a problem at some caves. Commercialization of caves may result in excessive disturbance (Mohr 1972) or intentional elimination by cave owners (Hall 1962). Other threats include exclusion of bats by poorly designed gates (as formerly at Long's Cave in Mammoth Cave National Park, Kentucky), changes in cave temperatures induced by opening additional entrances (Matthews and Moseley 1990) or poorly designed barriers to human access (Richter et al. 1993). Improperly constructed gates can alter the air flow, trap debris, and block the entrance by not allowing enough flight space (Brady et al. 1982). Altered exchange of air with the outside environment can cause significant changes in cave temperature and humidity (Currie pers. comm., 1992) and may cause the bats to abandon the cave. Improperly constructed gates may also subject the bats to severe predation as they attempt to pass through the gates (Tuttle 1977). Despite protection at overwintering sites, populations continue to decrease in several portions of their range, suggesting that the species is being negatively affected by disturbance or loss of summer habitat. Loss and degradation of summer habitat and roost sites due to impoundment, stream channelization, housing development, clearcutting for agricultural use (Herkert 1992), or incompatible forest management practices that result in a shortage of the microhabitats used for maternity roosts may be the primary factors in recent population declines (Gardner pers. comm., 1992; Refsnider pers. comm., 1992; Currie pers. comm., 1992; see also Sparks et al. 2005).|
|Conservation Actions:||The most important hibernacula are protected, as are many hibernation sites that support fewer numbers of M. sodalis. Maternity roosts generally are not permanent and are not suitable for long-term protection. Summer roosts need to be identified. Hibernacula should be adequately protected from human disturbance. Known maternity roosts should be protected; compatible forest management is most important for ensuring long-term availability of suitable summer habitat (see management information).|
|Citation:||Arroyo-Cabrales, J. & Álvarez-Castañeda, S.T. 2008. Myotis sodalis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 19 April 2015.|
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