Corynorhinus townsendii

This bat was included in the genus Plecotus by Handley (1959).

Large range spans North America; very large number of known roost sites and locations; substantial overall population size, but local populations tend to be small; overall recent trend not well known; apparently declining in abundance in portions of the range but stable or increasing in other areas; increasing in abundance in the east as a result of effective conservation measures; many roosts are vulnerable to disturbance and/or destruction (e.g., recreational caving or mine exploration, mine reclamation, and renewed mining in historic districts); not yet known to be afflicted by white-nose syndrome, but this fungal disease of bats now occurs throughout much of the eastern portion of the range of C. townsendii; currently not known to be threatened by mortality caused by wind turbines, but this might pose a threat in the future.

Range includes western North America from southern British Columbia south to the Isthmus of Tehuantepec (Mexico), west to the Pacific coast, eastward to the Black Hills of South Dakota and Edwards Plateau of Texas, with isolated populations in the gypsum caves of northeastern Texas, Oklahoma, and Kansas, and in limestone regions of Arkansas, Missouri, Illinois, Indiana, Ohio, Kentucky, Virginia, and West Virginia. Elevational range extends from near sea level to at least 3,300 meters in some areas.

According to Handley (1959), the range of subspecies townsendii includes southwestern British Columbia, western Washington, western Oregon, and northwestern and west-central California; this subspecies intergrades with subspecies pallescens over a wide area in central and northern California and northward between the Cascades and the Rockies; subspecific allocation of specimens from much of this area is uncertain; some authors have applied the subspecific name intermedius to populations in the area of intergradation (Handley 1959). Handley characterized the range of subspecies pallescens as extending from southern British Columbia southward through the western United States to northwestern Mexico; west to central Washington, central Oregon, eastern and southern California, Sonora, and islands in the Gulf of California; east to South Dakota, Kansas, western Oklahoma, and Texas. As defined by Handley, subspecies australis ranges from the mountains of central and northern Mexico to western Texas.

However, a range-wide study of molecular phylogeny by Piaggio and Perkins (2005) found that geographic patterns of genetic (DNA) variation do not conform with the ranges of subspecies townsendii and pallescens as defined by Handley based on morphological characteristics. Piaggio and Perkins (2005) concluded that subspecies townsendii is broadly distributed from the Pacific coast of the United States and British Columbia (including Vancouver Island) southward to coastal regions of the Sonoran Desert in Mexico, eastward to the Colorado Plateau and the Black Hills, whereas subspecies pallescens is much more restricted and ranges from New Mexico to central and eastern Colorado, where it reaches its northern limits in northern Colorado or southern Wyoming. The molecular phylogenetic results conformed with the geographic scope of australis as defined by Handley.

Subspecies ingens: Range includes the Ozark Highlands and Boston Mountains ecoregions in northeastern Oklahoma, northwestern Arkansas, and (at least formerly) southwestern Missouri.

Subspecies virginianus: Range encompasses the Appalachian Mountains in Virginia, West Virginia, North Carolina, and eastern Kentucky. Presently these bats occur in decreased numbers throughout much of the historical range. The largest colonies are in several caves in Pendleton County, West Virginia; some caves serve as both hibernation and maternity sites, others are primarily maternity caves. Colonies occur also in Lee County and surrounding counties, Kentucky (the best known site being Stillhouse Cave); in Bath, Highland, Rockingham, Bland, and Tazewell counties, Virginia (Dalton 1987); and in Avery and Watauga counties, North Carolina (including Black Rock Cliffs Cave) See Matthews and Moseley (1990) and Handley (1991).

The molecular phylogeny of Piaggio and Perkins (2005) agreed with the morphologically defined taxonomic/geographic scope of subspecies ingens and virginianus as defined by Handley (1959).

The number of distinct occurrences has not been determined using standardized criteria, but this species is represented by a very large number of known roost/observation sites and locations (as defined by IUCN).

These bats roost pendant-like on open surfaces of caves and abandoned mines (Western Bat Working Group 2005). Thus it is relatively unlikely to be missed in surveyed areas of caves and abandoned mines, even when present in low numbers (as is typical). However, recent studies indicate that use of roost sites is variable within seasons and among years, so multiple surveys may be required before use can be documented within an area (Western Bat Working Group 2005). Also, roosts can be very difficult to locate in some regions (particularly Canada and some desert areas) (Western Bat Working Group 2005).

Since 2008, the Subterranean Program of Bat Conservation International (BCI) has surveyed thousands of mines and caves across the United States, with a focus on the western and southwestern United States. During these surveys C. townsendii consistently was the most encountered bat. On BLM lands in the western United States, BCI surveyed 1,659 abandoned mine features and encountered a total of 211 C. townsendii in approximately 127 mines (K. Gillies, pers. comm., 2015).

In British Columbia, this species is represented by about 100 occurrences (not defined, but presumably based on roost sites) (Nagorsen 2013). In the 1990s, this species was represented in California by 37 known colonies (Pierson and Rainey 1998). In northern Utah, big-eared bats were found in day roosts in 196 caves and mines (none of 105 bridges) out of 676 mines and 39 caves surveyed; 13 were maternity roosts (Sherwin et al. 2000). In southwestern Colorado, Hayes et al. (2011) found C. corynorhinus in 38 of 133 mines surveyed. Townsend's big-eared bats were found in 9 of 25 abandoned mines surveyed in Durango, Mexico (López-González and Torres-Morales 2004).

Subspecies ingens: As of 2008, this subspecies was represented by 20 essential caves, including 10 maternity colonies, 8 hibernacula, and 2 used only in autumn; several caves are used both as a maternity site and hibernaculum (USFWS 2008). Several essential caves serve as alternate roosts for the same maternity colony (colony may move among the alternate caves during both the maternity season and between years) (USFWS 2008a). Same-year counts at maternity sites and hibernacula indicate that it is likely that major hibernacula have not yet been located (USFWS 2008a).

Subspecies virginianus: Currently known from 13 major (more than 200 bats) maternity colonies (USFWS 2008b).

The primary threat appears to be disturbance and/or destruction of roost sites resulting from: recreational caving or mine exploration; mine reclamation; renewed mining in historic districts; destruction/decay of buildings used as roosts, or reuse by people or deliberate exclusion of bats from such buildings (Western Bat Working Group 2005, Hayes and Wiles 2013)."In large portions of its western range, dependence upon abandoned mines puts this species at risk if mine reclamation and renewed mining projects do not mitigate for roost loss, or do not conduct adequate biological surveys prior to mine closure" (Western Bat Working Group 2005).

"Surveys conducted in Oregon and California indicate that current and historic roost sites have been negatively impacted by human visitation and renewed mining in recent years with most reported colonies exhibiting moderate to sizable reduction in numbers. Additional surveys in Utah indicate that several historic maternity sites have been abandoned, although it is not known if these colonies have relocated." Source: Western Bat Working Group 2005).

Nondestructive intrusion associated with research activities can negatively affect local colonies (Pearson et al. 1952), and capture and handling of bats in nursery roosts may cause the bats to vacate the site (Humphrey and Kunz 1976). Archeological excavations in Stanton’s Cave, Grand Canyon National Park, clearly caused roost abandonment. This cave was fenced for a few years and considerable activity in the front chamber caused high levels of disturbance in the form of in and out traffic, noise, and light (K. Gillies, pers. comm., 2015). Despite this sensitivity, careful nondestructive intrusion by researchers usually is not a significant problem; day-roosting individuals (López-González and Torres-Morales 2004) and females in maternity sites generally appear to be somewhat tolerant of disturbance (Sherwin et al. 2000; K. Gillies, pers. comm., 2015).

Both roosting and foraging areas may be negatively impacted by timber harvest practices and loss of riparian habitat (Western Bat Working Group 2005). See also Piaggio et al. (2009).

Activities associated with renewed oil exploration and extraction could negatively affect some populations of subspecies virginianus (see USFWS 2008b).

Since this species feeds largely on moths, pesticide spraying to control outbreaks of moth pests (e.g., spruce budworm, tussock moths, and Spongy Moth - Lymantria dispar) and other insects on forest and agricultural lands near roosts may affect overall moth abundance and might reduce food resources for this species (Hayes and Wiles 2013, Nagorsen 2013). However, population-level impacts of such pesticide use on this species are uncertain.

Lack of long-term protection is a conservation concern in some areas within the range of subspecies virginianus. Habitat loss and degradation from human activities are ongoing concerns, and all populations are vulnerable to significant losses from predation or vandalism (USFWS 2008b)

White-nose syndrome has not yet been documented as afflicting Townsend's big-eared bats, but this fungal disease of bats now occurs throughout much of the eastern portion of the range of C. townsendii, including caves used by C. townsendii (Stihler 2011a).

Mortality associated with wind turbines is a potential threat. Currently, turbines are not known to be a significant source of mortality (e.g., see USFWS 2008a, b), but they could become so as more turbines are installed throughout the range of the species (Miller et al. 2011).

Piaggio et al. (2009) found that population structuring estimated from mtDNA and microsatellites showed significant levels of differentiation among populations of C. t. virginianus located in different geographical regions. The authors stated that these levels of regional differentiation suggest a complete loss of connectivity among regional populations of C. t. virginianus among females and among males except between the northeastern and central West Virginia regions. Further, microsatellite data support loss of connectivity of these regional populations through evidence of population bottlenecks and inbreeding in some populations of C. t. virginianus (Piaggio et al. 2009).

Neither western subspecies (C. t. pallescens, C. t. townsendii) shows signs of a reduction in population genetic diversity (Piaggio et al. 2009).

Western subspecies townsendii and pallescens: The greatest threat is vandalism, and disturbance by humans; disturbance of a nursery colony or of a hibernating group may sometimes cause the bats to abandon the site and move to an alternate roost (Pearson 1952, Handley 1959). An additional threat is blockage of cave/mine entrances through collapse or human activities, including mine closures related to human safety issues (Perkins 1990; pers. comm., 1997; Wyoming State Wildlife Action Plan 2010). Habitat loss is also a threat.

Subspecies ingens: The historical decline probably was attributable mainly to human intrusion into caves, which depletes energy reserves of aroused bats and may lead to cave abandonment if disturbance is frequent (Pearson 1952, Handley 1959). Females exhibit limited dispersal, and individuals exhibit high natal philopatry, so extirpated colony site are unlikely to be naturally recolonized (Weyandt et al. 2005, USFWS 2008a). The occupied region is experiencing considerable human population growth and associated development; as a result, big-eared bat populations may be subject to increasing habitat loss and fragmentation, vandalism, and distubance (USFWS 2008a). Recreational use and associated human disturbance at maternity caves and hibernacula remain a major threat (USFWS 2008a). Likely there are as yet undiscovered major roosts, and threats to these are unknown (USFWS 2008a). Currently, disease and predation are not considered major threats (USFWS 2008a).

Subspecies virginianus: The growing popularity of spelunking is a tremendous threat to these bats. Very intolerant of disturbance in summer and winter. Former decline probably is attributable to human intrusion into caves, which depletes energy reserves of aroused bats and may lead to cave abandonment if disturbance is frequent. Forest defoliation by the introduced Spongy Moth (Lymantria dispar) could adversely affect native Lepidoptera and impact bat population (Sample and Whitmore 1993). In some areas, feral cats prey on the bats.

A relatively low degree of genetic diversity has been identified in populations of the endangered eastern subspecies, C. t. virginianus as inferred from both mtDNA and microsatellite DNA (Piaggio et al. 2009). "This reduced genetic diversity means that genetic drift may be driving diversity within these populations and the biodiversity and evolutionary potential of C. t. virginianus has been diminished" (Piaggio et al. 2009).