California mammals

Big Brown Bat in California

Eptesicus fuscus

Native to California SNR Unranked in California

Not listed as nonindigenous in California by USGS NAS; native to its California range.

IUCN Red List status

  1. LC
  2. NT
  3. VU
  4. EN
  5. CR
  6. EW
  7. EX

LC – Least Concern

Widespread and abundant; not at risk.

Big Brown Bats (Eptesicus fuscus)Big brown bat flying in daylight with wings spreadBig brown bat flying at night with wings spreadBig brown bat roosting on lichen-covered tree barkBig brown bat roosting on a wooden structure
Photo: Connor Long · CC BY-SA 4.0Big Brown Bats (Eptesicus fuscus)Photo: rhododendrites · CC-BY-SABig brown bat flying in daylight with wings spreadPhoto: Dan Riskin · CC-BYBig brown bat flying at night with wings spreadPhoto: Rita Clare · CC0Big brown bat roosting on lichen-covered tree barkPhoto: Bonnie Isaac · CC0Big brown bat roosting on a wooden structure

Big Brown Bat in California, by the numbers

Common in California 78th most recorded of 233 mammals logged in California

545 occurrence records
279 with iNaturalist photos

Records from 2000–2026.

545 total records count every California occurrence from GBIF and iNaturalist; the map plots a georeferenced sample of 300; the monthly chart covers the 511 records with a full observation date.

When to look for the Big Brown Bat in California

Most sightings fall in July to August.

511 California occurrence records (iNaturalist and GBIF) by month of year, 2000–2026. Shows when the species is recorded, not a guarantee of presence.

Monthly California records (table)
MonthRecords
January13
February2
March14
April33
May55
June82
July140
August94
September47
October17
November8
December6

Monthly big brown bat occurrence records (iNaturalist and GBIF) in California, 2000–2026.

Seasonality

Year-round in California, with recorded sightings peaking in July–August.

Occurrence map

Where Big Brown Bat has been recorded in California

300 records mapped · zoom and drag to explore

300 California records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
Santa Monica Mountains National Recreation Area 6
Cleveland National Forest 4
Hain Wilderness Area 4
San Gabriel Mountains National Monument 4
Joshua Tree National Park 3
Pinnacles National Park 3
Standish-Hickey State Recreation Area 2
Redwood National Park 2

Protected places with the most big brown bat sightings, from the USGS Protected Areas Database plus named mountain ranges, good spots to look, not a full breakdown, so they don't sum to the total.

Where it's recorded in California

CountyRecords
San Diego County 140
San Bernardino County 49
Riverside County 43
Los Angeles County 37
Imperial County 37
Marin County 15
San Benito County 15
Santa Cruz County 14
San Luis Obispo County 13
Mendocino County 10
Ventura County 10
Humboldt County 9
40 other counties 153

The complete county distribution, spread across 52 California counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

Big brown bat reporting rises sharply through late spring and summer in California. July leads the supplied series with 140 records, followed by August with 94 and June with 82; November through February are much quieter, though reports do not disappear entirely.

San Luis and Sacramento national wildlife refuges and the San Joaquin Valley provide the file’s geographic reference points, but no place counts rank them. The 545 records describe a warm-season concentration in reporting, not bat abundance at those sites or across California.

Occurrence data from iNaturalist and GBIF.

Big Brown Bats (Eptesicus fuscus)
Full species profile Big Brown Bat Eptesicus fuscus Size 7.5 cm3 in Weight 17 g0.6 oz Lifespan 19 yr View the full profile

More mammals in California in the atlas

Data & sources

The data and visualizations on this page draw on these open sources:

  • GBIFCC-BY 4.0occurrence records behind the range map, elevation, and record counts
  • iNaturalistCC0 / CC-BY / CC-BY-SAobservations, photos, and audio recordings
  • NatureServe ExplorerCC-BYthe state conservation rank
  • IUCN Red Listattributed factthe global conservation status
  • USGS NASpublic domainnative / introduced status
  • Natural Earthpublic domainthe relief basemap
  • USFSpublic domainnational-forest boundaries
  • USGS Protected Areas Databasepublic domainthe named parks, forests, and refuges behind "notable places to look"