Myotis yumanensis

Myotis yumanensis and M. lucifugus can be difficult to distinguish in the field (Nagorsen and Brigham 1993, Verts and Carraway 1998), and Harris (1974) proposed the existence of "occasional possible hybrids" between M. yumanensis and M. lucifugus carissima. However, the two species exhibit a high level of genetic divergence throughout western North America, with no genetic evidence of hybridization (Herd and Fenton 1983, Zinck et al. 2004). Weller et al. (2007) used echolocation calls and forearm length to distinguish most specimens of the two species in the Pacific Northwest.

Widespread distribution in western North America; large number of roosts in natural and human-made structures; occurs in pristine and altered habitats; large population size, locally common; locally vulnerable to roost disturbance and loss; apparently secure throughout much of range, but distribution, roost requirements, and threats in winter are poorly known.

Patchy distribution includes western North America from British Columbia south through the western United States to Hidalgo, Morelos, Michoacan, and Baja California, Mexico; east to Montana, western panhandle of Oklahoma, and western Texas (mainly lowlands along the Rio Grande, and the Chisos Mountains) (Barbour and Davis 1969; Nagorsen and Brigham 1993; Adams 2003; Simmons, in Wilson and Reeder 2005; Reid 2006; Roehrs et al. 2008; Ammerman et al. 2012).

The number of distinct occurrences has not been determined using standardized criteria, but this species is represented by a large number of collection/observation sites and roosts (GBIF database). For example, Nagorsen and Brigham (1993) mapped approximately 70 collection sites in British Columbia, and Verts and Carraway (1998) mapped 88 collection localities in Oregon.

Overall, no major threats are known, but the species appears to be subject to ongoing slow reduction of available roost sites, localized detrimental effects of roost disturbance by humans, and degradation of foraging habitat; scope and severity of threats in wintering sites are poorly known.

Locally, some occurrences may be threatened by human disturbance of maternity colonies in caves and buildings (Schmidly 1991, Verts and Carraway 1998, Ammerman et al. 2012). This species also may be affected by the closure of abandoned mines without adequate surveys. Frequently this bat occurs in human-made structures and is vulnerable to destructive pest control activities. Some riparian management practices may be detrimental and result in loss of potential roost sites (Western Bat Working Group 1998, Arizona Game and Fish Department 1993).

Livestock grazing may be affecting the foraging habitat and food resources of this species over much of its range, but the severity of the effect is unknown.

Threats in Texas are not well known but potentially include pesticide use and changes in vegetation caused by invasive plant species (e.g., salt cedar, giant cane) (Ammerman et al. 2012). Changes in vegetation due to invasive plant species also have occurred over much of the species' range, but the effects of these alterations on bats are unknown.

Some types of environmental contaminants may temporarily reduce survival of certain segments of a contaminant-exposed population but not have serious overall population impacts. In California in the 1990s, populations exposed to a chemical (metam sodium) spill exhibited a period of reduced survival of juvenile females but not adult females (compared to control populations), but there was an increase in survival for both stage-classes across all populations during the study period (this may have been caused by the end of an extended drought in California), and population growth rates increased during the four-year period (Frick et al. 2007). Differences in food availability among the exposed and control populations were not measured, but aquatic insect populations presumably were reduced for the exposed populations. Contaminant levels in the exposed bats apparently were not measured.

This species is not known to incur significant mortality from turbines at wind energy facilities (Arnett and Baerwald 2013).

Climate change (drought) may reduce the availability of water resources in much of the range of this species; this could reduce bat reproduction (Adams 2010), but population impacts are as yet undocumented.

As of early 2015, this species was not known to be affected by white-nose syndrome.