|Scientific Name:||Myotis austroriparius|
|Species Authority:||(Rhoads, 1897)|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Arroyo-Cabrales, J. & Álvarez-Castañeda, S.T.|
|Reviewer(s):||Medellín, R. & Schipper, J.|
This species is listed as Least Concern in because of its wide distribution, presumed large population, occurrence in a number of protected areas, and because it is unlikely to be declining at nearly the rate required to qualify for listing in a threatened category.
|Range Description:||The range of this bat includes the southeastern United States, west to southeastern Oklahoma and eastern Texas (Mirowsky et al. 2004, Schmidly 2004), north in the Mississippi River drainage through Arkansas, Mississippi, western Tennessee, southeastern Missouri, and western Kentucky to southern Illinois (Hofmann et al. 1999) and southern Indiana, and east to southeastern Virginia (Hobson 1998), southern North Carolina, South Carolina (Menzel et al. 2003), Georgia, and Florida (Jones and Mamming 1989). Summer and winter ranges are the same. Although widespread in southeast, the vast majority of the known population is concentrated in northern Florida, and the species is rare and local outside the Gulf coastal plain.|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Considering the total number of maternity roosts, hibernacula, and other occupied roosts and habitat, there are certainly more than 100 occurrences or subpopulations (Gore and Hovis 1992; Horner and Mirowsky 1996; Clark pers. comm.). Total adult population size is unknown but is at least in the 100,000s. This species is still abundant in some places. Florida has at least 18 current or former maternity caves which, in past years, potentially contained 400,000 adult females; a 1991 survey found only eight maternity caves with a total of less than 200,000 adult females (Gore and Hovis 1992). The number of individuals estimated from known tree roosts and man-made structures is much smaller (less than 500; Clark pers. comm.; Gore pers. comm.), but it is difficult to locate such roosts, and undoubtedly there are more.|
|Habitat and Ecology:||
The number of occurrences or subpopulations with good or excellent estimated viability may be fewer than 30 (more than 50 percent of these are in Florida). Recent surveys (e.g., Hofmann et al. 1999, Mirowsky et al. 2004) suggest that the number of small maternity colonies may be quite large, but these are of uncertain viability. Only two large (more than 100 bats) winter colonies have been reported in recent years, but there are several small colonies throughout the species range. In Florida, large numbers form maternity colonies in caves; the species has been reported a few times in buildings. Maternity colonies also have been found in a small number of caves in Georgia and Alabama. In the rest of the deep south, these bats generally use buildings and other structures, mines, and hollow trees (e.g., water tupelo, black gum, water hickory, bald cypress) for spring and summer roosts. In Louisiana, a hollow water tupelo (Nyssa aquatica) studied in late summer and early fall contained about 50 individuals (Gooding and Langford 2004). By winter in this region they roost in small groups in outdoor sites, often over water, such as bridges, culverts, storm sewers, and boat houses, as well as in hollow trees (Barbour and Davis 1969). In Florida (and perhaps elsewhere) these bats also roost in caves in winter; apparently they may use different caves for summer and winter roosts (Gore and Havis 1992). In the north, the pattern of cave use is different. Kentucky populations winter in caves (often with Myotis sodalis) but are rare in most caves in the summer, when most roost in large hollow trees. The few old records from Indiana also were mostly from caves in winter. Summer roost sites are poorly known from this part of their range. At least one cave in Indiana had bats every month except May, June, and July (Mumford and Whitaker 1982). Only a few maternity colonies have been reported in this region: one was in the Kentucky cave already mentioned; additional maternity colonies exist in southern Illinois, where one was in a hollow-based water tupelo (Nyssa aquatica) (Hofmann et al. 1999).
The key characteristics for maternity sites are high humidity and constant warm temperatures. Foraging habitat is riparian floodplain forests or wooded wetlands with permanent open water nearby (Gardner et al. 1992). These bats may forage primarily over lakes, ponds, or slow-moving streams.
Florida populations declined by about 50% from some 400,000 adult females in the 1950s (Rice 1957) to less than 200,000 females in 1991 (Gore and Hovis 1992). Not only did numbers of bats decline, but number of caves used as maternity roosts also declined by nearly 50% (from 15 to 18) in Florida over the same period. There is no indication that the population has stabilized. Some caves occupied in the early 1980s are no longer occupied (Gore and Hovis 1992). However, Brown (1997) reported that this species is adaptable and seems to be holding its own in the southeastern United States.
While the Florida population was thriving in the 1960s, Barbour and Davis (1969) reported that the Ohio River Valley population was steadily declining and apparently nearing extirpation. Current data from this northern range indicates that populations are still present in low numbers, although their status remains largely unknown. Indiana populations had declined considerably by 1980 (Mumford and Whitaker 1982), although populations were always small. Recent extensive searches in Illinois indicated that the population has become more restricted than in the past; only one hibernating colony was located, compared to nine previously known hibernating sites, and the bats were only found in four counties compared to six in the past. Georgia has 12 older records (before 1970), and only one record since 1970, but this change could be due to lack of searching. Recent field studies in coastal North Carolina, South Carolina, and eastern Texas have located populations of this species, but there are no baseline data with which to compare trends. Declines likely have resulted from various factors, especially human disturbance and physical alteration of caves used as hibernacula and maternity sites (Gore and Hovis 1992). Excessive human visitation may awaken bats and cause them to use up fat reserves. In maternity colonies, disturbance may cause females to abandon their young. Heavy collecting or banding may cause a population to vacate a site. Attempts to collect, even in winter, usually result in bats vacating at least temporarily (Mumford and Whitaker 1982). In addition, some caves have been made unavailable or degraded by the closing off of their entrances, installation of bat-impermeable barriers, forest removal around entrances, or by flooding by reservoirs. Loss of upland roosts increases vulnerability to mortality from sudden flooding. One cave formerly used by 11,000 individuals was turned into a public dump and virtually abandoned by bats. Clearing and draining of bottonland hardwood forest wetlands likely have reduced available habitat for summer roosting and foraging. The indirect effects of pesticide use are unknown.
|Conservation Actions:||There are several protected occurrences in Florida; also Bat Cave in Kentucky. Several caves in Jackson County, Florida, are protected due to use by endangered M. grisescens. The species is afforded nominal protection via Florida's Cave Protection Act. Bat Conservation International, TNC, and the state of Florida were instrumental in protecting Judge's Cave; a few other maternity caves on private land in Florida have various levels of protection (Gore and Hovis 1992). South Carolina has used posting and controlled access to roost sites to protect this species (Bunch pers. comm.). One occurrence in Indiana is in a state park and is protected. In Texas, two maternity roosts are in state parks and one is in a national wildlife refuge, and populations are known to exist in other state parks and wildlife management areas, national forests, Big Thicket National Preserve, and Nature Conservancy lands. Determine status and trend in South Carolina, Georgia, Louisiana, Texas, Arkansas, and Tennessee. Protect roosting sites of all large (> 100) colonies, both breeding and wintering. Protect frequently used foraging habitat in their natural forested state. Obtain more information about summer and winter roosting requirements. Determine viability and importance of small maternity colonies. Develop techniques for monitoring with minimum disturbance. Determine effects of disturbance on survival and reproductive success. Determine dispersal distances and roosting sites for bats when away from the large cave colony sites. Determine importance of hollow trees and other non-cave sites as maternity roosts.|
|Citation:||Arroyo-Cabrales, J. & Álvarez-Castañeda, S.T. 2008. Myotis austroriparius. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 03 September 2015.|
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