Eptesicus fuscus

Mônico and Soto-Centeno (2024) elevated Eptesicus fuscus dutertreus to species status; subspecies include bahamensis, dutertreus, hispaniolae, lynni, petersoni, and wetmorei. The status of E. guadeloupensis is unresolved, with some including it as a subspecies of dutertreus (ASM 2025, Simmons and Cirranello 2025, Yi and Latch 2022), while Mônico and Soto-Centeno (2024) continue to recognize it as a valid taxon in the "absence of additional data to evaluate". E. fuscus is retained in the genus Eptesicus, while all other species in the genus have been moved to Neoeptesicus (American species) or Cnephaeus (Afro-Eurasian species) (ASM 2025).

Very large range extends from North America to northern South America; common in much of range; large number of roosts and locations; uses a wide range of habitats; readily uses human-made structures as roosts; fatalities occur at wind energy facilities but probably have little effect on the overall population; population affected to unknown degree by white-nose syndrome (WNS) in eastern North America, but often uses non-cave hibernation sites that are not conducive to development of WNS.

Range extends from Alaska and southern Canada (including all provinces bordering the United States) south to northern Colombia, northwestern Venezuela, and northern Brazil; all Mexican states except those of Yucatan Peninsula (in northern Mexico most prevalent in eastern and western Sierra Madre bordering arid midlands of Mexican Plateau); in and along the central mountain chain in Central America (Honacki et al. 1982; Kurta and Baker 1990; Jones 1989; Koopman, in Wilson and Reeder 1993).

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

On a range-wide scale, no major threats have been identified. Regionally or locally, the following factors may be significant.

This is one of several bat species that may be affected by white-nose syndrome (WNS). WNS is caused by a cold-loving fungus and has killed millions of cave-roosting bats in eastern North America since 2007. However, WNS has not been detected in most of the range of E. fuscus. Additionally, big brown bats frequently hibernate in human-associated sites (e.g., buildings, where WNS is not known to thrive), as well as in caves and mines, so these bats may be less vulnerable to severe WNS-caused population declines than are bats that hibernate only in caves or mines. Furthermore, in caves in New York, WNS caused severe declines in Myotis lucifugus but did not affect E. fuscus, which appeared to be resistant to WNS (Frank et al. 2014).

Because E. fuscus appears to be a habitat generalist, readily uses human-made structures as roosts, and takes advantage of insect concentrations near lights, habitat is probably a less important conservation component than it is for other bats. However, current forestry practices may have a negative impact on tree-roosting bat species, and foraging activity has been shown to decrease with increasing urbanization, possibly because of lower insect abundance (Agosta 2002).

Big brown bats and other species that roost in buildings are often perceived as a nuisance and are vulnerable to exclusion and eradication attempts (Pierson 1998, Agosta 2002).

Although this species is nonmigratory or a short-distance migrant, it incurs significant mortality at some wind energy facilities in the Midwest (Jain et al. 2011, Grodsky et al. 2012). Throughout most of eastern North America, wind-turbine kills of this species are common but much less frequent than those of hoary, eastern red, and silver-haired bats (Johnson 2005, Arnett et al. 2008). Overall, Arnett and Baerwald (2013) estimated that approximately 26,000-52,300 E. fuscus were killed at wind energy facilities in the United States and Canada during the period 2000-2011.