Myotis grisescens 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Chiroptera Vespertilionidae

Scientific Name: Myotis grisescens A.H. Howell, 1909
Common Name(s):
English Gray Myotis, Grey Bat

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Arroyo-Cabrales, J. & Timm, R.
Reviewer(s): Medellín, R. (Chiroptera Red List Authority) & Schipper, J. (Global Mammal Assessment Team)
Listed as Near Threatened because the species is considered threatened at the U.S. Fish and Wildlife Service but there are several recuperation programmes for this species reaching at the moment more than 1 million individuals. This species can be considered as a success for the conservation programmes carried out in USA. It could approach the criteria A1 for Vulnerable, considering that until the 80s the declining in the population was larger than 50%.
Previously published Red List assessments:

Geographic Range [top]

Range Description:The range extends from southeastern Kansas and central Oklahoma east to western Virginia and western North Carolina, and from Missouri, Illinois, and Indiana south to southern Alabama and northwestern Florida (Decher and Choate 1995); occurs primarily in the cave region of Missouri, Arkansas, Kentucky, Tennessee, and Alabama. Summer and winter ranges are essentially the same.
Countries occurrence:
United States
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Total population was estimated at 1.5 million in the early 1980s. About 10,000 are thought to occur in Florida in summer, a few hundred in winter (Humphrey 1992). Five gated maternity caves in Oklahoma each include 10,000 or 20,000 bats (Hensley 2003). Since listing, several critical hibernation caves have been gated, leading to stable and growing population in many areas.
Current Population Trend:Increasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:About 95% of entire known population hibernates in eight or nine caves, over half in one cave. Roost sites are nearly exclusively restricted to caves throughout the year (Hall and Wilson 1966, Barbour and Davis 1969, Tuttle 1976), though only a few percent of available caves are suitable (Tuttle 1979). Winter roosts are in deep vertical caves with domed halls. Large summer colonies utilize caves that trap warm air and provide restricted rooms or domed ceilings; maternity caves often have a stream flowing through them and are separate from the caves used in summer by males. Occasionally non-cave roost sites are used. Hays and Bingman (1964) reported a colony in a storm sewer in Pittsburg, Kansas and, in 1988, a maternity colony was discovered using a storm sewer in Kansas (Decher and Choate 1988). Harvey and McDaniel (1988) located a maternity colony in a storm sewer in downtown Newark, Independence County, Arkansas. There are occasional reports of mines (Sealander 1979, Thom 1981, Brack et al. 1984, Harvey and McDaniel 1988) and buildings (Gunier and Elder 1971) being used as roost sites. Winter caves are deep and vertical and provide a large volume of air below the lowest entrance that acts as a cold air trap (Tuttle 1976). Cold air flows in and is trapped during successive winters, providing mean annual temperatures 6 degrees C or more below the above-ground mean annual temperature (Tuttle 1978). Winter cave temperatures range from 6 to 11 degrees C (Tuttle 1979). In the summer, maternity colonies prefer caves that act as warm air traps or that provide restricted rooms or domed ceilings that are capable of trapping the combined body heat from thousands of clustered individuals (Tuttle 1975, Tuttle and Stevenson 1977). Cave temperatures range from 14 to 24 C. Undisturbed summer colonies may contain up to 250,000 bats, and average 10,000 to 25,000 (Tuttle 1979). Summer caves are nearly always located within 1 km of a river or reservoir over which the bats forage (Tuttle 1979). Tuttle (1979) showed that forested areas along the banks of streams and lakes provide important protection for adults and young. Young often feed and take shelter in forest areas near the entrance to cave roosts (Tuttle 1979). Do not feed in areas along rivers or reservoirs where the forest has been cleared (LaVal et al. 1977; Tuttle and Stevenson, in prep.).

Yearlings and adult males segregate into nomadic summer colonies that tend to roost in caves within a few kilometers of ones selected by adult females (Layne 1978).

Threats [top]

Major Threat(s): Abundance declined by at least 50% from the 1960s to the early 1980s (Brady et al. 1982). The number of occupied caves has substantially decreased. In Missouri, 26 of 66 caves used historically by this species and surveyed in 1994 showed no evidence of recent use. See Layne 1978 for information on decline in Florida.

Cave disturbance has been the major factor in the decline. Cave protection efforts have greatly reduced this threat.

Although there are apparently few current threats, the use of forestry insecticides and crop pesticides in areas adjacent to riparian corridors where gray bats forage may reduce the prey base or kill bats that ingest contaminated insects (Northern Prairie Wildlife Research Center). Some maternity and hibernating colonies are susceptible to human disturbance (Northern Prairie Wildlife Research Center).

Decline began with cave disturbance associated with saltpeter production during the Civil War. Some of the largest colonies were lost as a result of cave commercialization. Some caves were improperly gated.

The species is especially vulnerable due to its high fidelity to particular favoured caves, and it is very sensitive to disturbance, including the mere presence of humans with lights; disturbance may result in bats moving to less favourable roosting places.

Other threats include pesticides, deforestation, and impoundment of waterways (and subsequent cave inundation).

Conservation Actions [top]

Conservation Actions: Cave protection efforts have led to recent population increases. By 1991, the rangewide population was stable and perhaps growing, apparently due to successful cave protection efforts. Since 1981, the maternity colony population in Oklahoma has increased from 56,000 to almost 150,000 (Hensley 2003).

The recovery plan criteria for change from endangered status to threatened status is documentation of permanent protection of 90% of Priority 1 hibernacula and documentation of stable or increasing populations at 75% of Priority 1 maternity caves during a period of five years; recent studies indicate that these criteria have been met (Harvey and Currie 2002).

The Tennessee Valley Authority sponsored a recovery project that resulted in the protection of two critical maternity sites: the Hambrick and Nickajack caves in Tennessee. Blowing Wind Cave in northern Alabama, the most important summer cave known for gray bats, has been acquired by the U.S. Fish and Wildlife Service and a gate has been placed across the entrance. Fern Cave, the largest known gray bat hibernaculum, has also been purchased by the Fish and Wildlife Service and is being managed for protection of the bats. The U.S. Fish and Wildlife Service also has acquired and protects additional caves in Alabama. To protect habitat, The Nature Conservancy has established six voluntary protection agreements with private landowners for gray bat maternity sites. The National Park Service restricts human access to six gray bat maternity caves on its lands and monitors them for possible disturbance. The Indiana Bat and Gray Bat Comprehensive Plan contains a detailed list of caves that have been protected or are currently being managed.

Identify all caves used for different stages of the life history. Occupied caves should be protected from human disturbance.

A buffer of undisturbed vegetation should be left around the entrances of caves inhabited by gray bats; wooded travel corridors between roosting and foraging sites should be protected; the use of herbicides and pesticides in areas adjacent to foraging and roost sites should be carefully controlled and monitored for unanticipated adverse effects (Alabama Forestry Commission).

Citation: Arroyo-Cabrales, J. & Timm, R. 2008. Myotis grisescens. The IUCN Red List of Threatened Species 2008: e.T14132A4403493. . Downloaded on 23 September 2018.
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