Washington mammals

Big Brown Bat in Washington

Eptesicus fuscus

Native to Washington S4 Apparently Secure in Washington

Not listed as nonindigenous in Washington by USGS NAS; native to its Washington 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 Washington, by the numbers

Occasional in Washington 60th most recorded of 145 mammals logged in Washington

127 occurrence records
41 with iNaturalist photos
Jul 7, 2026 Last seen in Washington

Records from 2000–2026.

127 total records count every Washington occurrence from GBIF and iNaturalist; the map plots a georeferenced sample of 124; the monthly chart covers the 123 records with a full observation date.

When to look for the Big Brown Bat in Washington

Most sightings fall in August.

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

Monthly Washington records (table)
MonthRecords
January1
February0
March1
April5
May11
June18
July24
August43
September12
October6
November0
December2

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

Seasonality

Year-round in Washington, with recorded sightings peaking in August.

Occurrence map

Where Big Brown Bat has been recorded in Washington

124 records mapped · zoom and drag to explore

124 Washington records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
San Juan Islands National Monument 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 Washington

CountyRecords
King County 34
Thurston County 13
Klickitat County 8
Pierce County 8
Kitsap County 6
Snohomish County 6
Spokane County 5
San Juan County 4
Lewis County 4
Yakima County 4
Kittitas County 4
Skagit County 3
14 other counties 28

The complete county distribution, spread across 26 Washington counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

For Washington, the big brown bat has a 127-record occurrence file covering 2000 to 2026. Of those, 41 come from iNaturalist and 110 from GBIF, so the two feeds overlap.

The monthly series reaches its high point in August (43 records), compared with none in February or November. The only named place with records is the San Juan Islands National Monument, with 2. This is documented occurrence, with no basis for converting record totals into animal numbers.

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 Washington 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"