SpeciesFacts

All species › Mammals › Big Brown Bat

Big Brown Bat

Eptesicus fuscus

Mammal · family Vespertilionidae · order Chiroptera

  1. G1
    Critically imperiled
  2. G2
    Imperiled
  3. G3
    Vulnerable
  4. G4
    Apparently secure
  5. G5
    Secure

NatureServe global rank G5: secure[2].

Updated October 30, 2026. Published by Humblebee.

Big Brown Bat
Photo: Rhododendrites, CC BY-SA 4.0, via Wikimedia Commons.
Endangered Species Act
Not listed[1]
NatureServe global rank
G5 Secure[2]
Native in
49 states[3]
Longest recorded life
19 years[4]

The Big Brown Bat (Eptesicus fuscus) is a mammal in the bat order, Chiroptera[5]. It is not listed under the US Endangered Species Act and NatureServe ranks it Secure worldwide[2][1].

Conservation status

NatureServe gives the Big Brown Bat a global rank of G5 and a national rank for the United States of N5, and both mean Secure[2][6]. It is not listed as Endangered or Threatened under the US Endangered Species Act in USFWS data checked on 2026-10-30[1]. NatureServe estimates the adult population at 100,000 to more than 1,000,000 bats[7]. The recent trend is uncertain, and NatureServe says numbers may have dropped somewhat where white-nose syndrome has hit bats in eastern North America[8].

Status Value
Endangered Species Act[1] Not listed
NatureServe global rank[2] G5 (Secure)
NatureServe US rank[6] N5 (Secure)
Total population (NatureServe estimate)[7] 100,000 to >1,000,000 individuals

Where Big Brown Bat lives

NatureServe lists the Big Brown Bat as native in 49 US states and territories, including the District of Columbia[3]. That covers states from Maine and Florida in the east to Washington and California in the west[3]. A state list shows where NatureServe records the bat, not a promise that you will see one there[3]. NatureServe also gives each state its own conservation rank[9].

Alaska: not recordedAKMaine: native, state rank S4MEWisconsin: native, state rank S4WIVermont: native, state rank S4VTNew Hampshire: native, state rank S3NHWashington: native, state rank S4WAIdaho: native, state rank S3IDMontana: native, state rank S4MTNorth Dakota: native, state rank SNRNDMinnesota: native, state rank S3MNIllinois: native, state rank S5ILMichigan: native, state rank S5MINew York: native, state rank S5NYMassachusetts: native, state rank S4MAOregon: native, state rank S4ORNevada: native, state rank S3NVWyoming: native, state rank S5WYSouth Dakota: native, state rank S5SDIowa: native, state rank S4IAIndiana: native, state rank S4INOhio: native, state rank SNROHPennsylvania: native, state rank S4PANew Jersey: native, state rank S3NJConnecticut: native, state rank S5CTRhode Island: native, state rank S5RICalifornia: native, state rank SNRCAUtah: native, state rank S4UTColorado: native, state rank S5CONebraska: native, state rank S5NEMissouri: native, state rank S4MOKentucky: native, state rank S5KYWest Virginia: native, state rank S5WVVirginia: native, state rank S5VAMaryland: native, state rank S4MDDelaware: native, state rank S5DEArizona: native, state rank S4AZNew Mexico: native, state rank S5NMKansas: native, state rank S5KSArkansas: native, state rank S4ARTennessee: native, state rank S5TNNorth Carolina: native, state rank S5NCSouth Carolina: native, state rank S4SCDistrict of Columbia: native, state rank S4DCOklahoma: native, state rank SNROKLouisiana: native, state rank S3LAMississippi: native, state rank S5B,S5NMSAlabama: native, state rank S5ALGeorgia: native, state rank S5GAHawaii: not recordedHITexas: native, state rank S5TXFlorida: native, state rank S3FLPuerto Rico: not recordedPR
State presence as recorded by NatureServe[9].
Show state ranks (49 states)
StateRankMeaning
AlabamaS5Secure
ArizonaS4Apparently Secure
ArkansasS4Apparently Secure
CaliforniaSNRNot Ranked
ColoradoS5Secure
ConnecticutS5Secure
DelawareS5Secure
District of ColumbiaS4Apparently Secure
FloridaS3Vulnerable
GeorgiaS5Secure
IdahoS3Vulnerable
IllinoisS5Secure
IndianaS4Apparently Secure
IowaS4Apparently Secure
KansasS5Secure
KentuckyS5Secure
LouisianaS3Vulnerable
MaineS4Apparently Secure
MarylandS4Apparently Secure
MassachusettsS4Apparently Secure
MichiganS5Secure
MinnesotaS3Vulnerable
MississippiS5B,S5NSecure (breeding), Secure (nonbreeding)
MissouriS4Apparently Secure
MontanaS4Apparently Secure
NebraskaS5Secure
NevadaS3Vulnerable
New HampshireS3Vulnerable
New JerseyS3Vulnerable
New MexicoS5Secure
New YorkS5Secure
North CarolinaS5Secure
North DakotaSNRNot Ranked
OhioSNRNot Ranked
OklahomaSNRNot Ranked
OregonS4Apparently Secure
PennsylvaniaS4Apparently Secure
Rhode IslandS5Secure
South CarolinaS4Apparently Secure
South DakotaS5Secure
TennesseeS5Secure
TexasS5Secure
UtahS4Apparently Secure
VermontS4Apparently Secure
VirginiaS5Secure
WashingtonS4Apparently Secure
West VirginiaS5Secure
WisconsinS4Apparently Secure
WyomingS5Secure

Diet and lifespan

The Big Brown Bat eats only invertebrates, according to EltonTraits[10]. Females reach sexual maturity at 547 days old[11]. A typical litter is 2 young and gestation lasts about 35 days[12][13]. The oldest known wild Big Brown Bat lived 19 years, which is a record and not a typical lifespan[4].

Trait Value
Longest recorded lifespan (AnAge)[4] 19 years (wild)
Litter or clutch size[12] 2
Gestation or incubation[13] 35 days
Female maturity[11] 547 days (about 1.5 years)
Active[14] nocturnal

Estimated diet composition (EltonTraits 1.0)[10]

  • 100% invertebrates

When to look for it

The Big Brown Bat is nocturnal, which means it is active at night[14]. GBIF observation records in the United States are highest in June, July and August[15]. Records show when people look and report, not how many bats there are[15].

January: 641 recordsJanFebruary: 709 recordsFebMarch: 641 recordsMarApril: 995 recordsAprMay: 1,742 recordsMayJune: 2,934 recordsJunJuly: 5,089 recordsJulAugust: 5,103 recordsAugSeptember: 1,833 recordsSepOctober: 769 recordsOctNovember: 573 recordsNovDecember: 557 recordsDec
US observation records on GBIF by month, all years. The three months with the most records are highlighted. Records show when people look and report, not how many animals there are[15].
Show records by month
MonthRecords
January641
February709
March641
April995
May1,742
June2,934
July5,089
August5,103
September1,833
October769
November573
December557

Where to see it

National Park Service species lists record Big Brown Bat as present in 183 park units[16]. Present means the park has a confirmed record, not that sightings are common.

And 159 more park units.

States with the most GBIF observation records: California, Colorado, Indiana, Michigan, New Mexico[17]. These counts follow where people look and report, not population size.

Safety around this animal

These tips are quoted in summary from official agencies. We add no advice of our own. Follow local rules and the agency pages linked below.

From Centers for Disease Control and Prevention

  • In the United States, the animals most often found with rabies are bats, skunks, raccoons and foxes.
  • Rabies spreads mainly through bites and scratches. It is fatal once symptoms start but preventable with prompt care.
  • Contact with bats is the leading cause of human rabies deaths in the United States.
  • After a bite or scratch, wash it right away with soap and water and get medical care urgently. Keep wildlife wild by staying away.

Source: Centers for Disease Control and Prevention[18]

Questions people ask

Is the Big Brown Bat endangered?
No. It is not listed as Endangered or Threatened under the US Endangered Species Act[1]. NatureServe ranks it G5, Secure, globally and N5, Secure, in the United States[2][6].
Where does the Big Brown Bat live?
NatureServe lists it as native in 49 US states and territories, including the District of Columbia[3].
What does the Big Brown Bat eat?
EltonTraits estimates its diet is 100% invertebrates[10].
How long does the Big Brown Bat live?
The longest recorded lifespan is 19 years in the wild[4]. That is a record, not a typical lifespan.
When is the Big Brown Bat seen?
It is nocturnal[14]. GBIF records in the United States peak in June, July and August[15].

Facts and sources

  1. Big Brown Bat is not listed as endangered or threatened under the US Endangered Species Act in USFWS ECOS data (checked 2026-10-30). USFWS ECOS
  2. NatureServe global conservation status rank for Big Brown Bat: G5 (Secure). NatureServe Explorer
  3. NatureServe lists Big Brown Bat as native in 49 US states and territories: Alabama, Arkansas, Arizona, California, Colorado, Connecticut, the District of Columbia, Delaware, Florida, Georgia, Iowa, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana,... NatureServe Explorer
  4. Maximum recorded lifespan in AnAge: 19 years in the wild. This is a record, not a typical lifespan. AnAge
  5. Big Brown Bat (Eptesicus fuscus) is a mammal in the family Vespertilionidae, order Chiroptera. NatureServe Explorer
  6. NatureServe national rank in the United States: N5 (Secure). NatureServe Explorer
  7. NatureServe estimate of total adult population (global, as a range): 100,000 to >1,000,000 individuals. NatureServe Explorer
  8. NatureServe notes on trend for Big Brown Bat. NatureServe Explorer
  9. NatureServe state ranks for Big Brown Bat (map and table on this page). NatureServe Explorer
  10. Estimated diet composition in EltonTraits 1.0: 100% invertebrates. EltonTraits 1.0
  11. Age at female sexual maturity in AnAge: 547 days (about 1.5 years). AnAge
  12. Typical litter or clutch size in AnAge: 2. AnAge
  13. Gestation or incubation period in AnAge: 35 days. AnAge
  14. Activity time in EltonTraits 1.0: nocturnal. EltonTraits 1.0
  15. GBIF observation records of Big Brown Bat in the US by month (chart on this page). GBIF
  16. NPSpecies park lists recording Big Brown Bat as present (list on this page). NPS NPSpecies
  17. US states with the most GBIF observation records of Big Brown Bat: California, Colorado, Indiana, Michigan, New Mexico. Record counts follow observer effort, not population size. GBIF
  18. Safety guidance from Centers for Disease Control and Prevention. CDC

Status, range and habitat come from NatureServe Explorer (CC BY 4.0) and USFWS ECOS at the snapshot date. Listings change by federal rule. State lists are where NatureServe records the species, not a promise that you will see it there. Never name a place smaller than a state. GBIF and park records count observations and checklists. They show where and when people report the species, not how many animals live there.

NatureServe. 2026. NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org. (Accessed: October 30, 2026). Licensed under CC BY 4.0; SpeciesFacts selected and summarized it.

Photo: Rhododendrites, CC BY-SA 4.0, via Wikimedia Commons.