Michigan mammals

Big Brown Bat in Michigan

Eptesicus fuscus

Native to Michigan S5 Secure in Michigan

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

Occasional in Michigan 31st most recorded of 75 mammals logged in Michigan

1,236 occurrence records
221 with iNaturalist photos
Jun 29, 2026 Last seen in Michigan

Records from 2000–2026.

1,236 total records count every Michigan occurrence from GBIF and iNaturalist; the map plots a georeferenced sample of 300; the monthly chart covers the 1,178 records with a full observation date.

When to look for the Big Brown Bat in Michigan

Most sightings fall in August.

1,178 Michigan occurrence records (iNaturalist and GBIF) by month of year, 2000–2026. Shows when the species is recorded, not a guarantee of presence.

Monthly Michigan records (table)
MonthRecords
January60
February71
March67
April74
May121
June95
July141
August344
September74
October31
November52
December48

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

Seasonality

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

Occurrence map

Where Big Brown Bat has been recorded in Michigan

300 records mapped · zoom and drag to explore

299 Michigan records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
Rose Lake State Wildlife Area 9
Kellogg Biological Station and Experimental forest 5
Isle Royale National Park 3
Ottawa National Forest 2
Manistee National Forest 2
Gratiot-Saginaw State Game Area 2
Maybury State Park 1
Huron National Forest 1

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 Michigan

CountyRecords
Ingham County 226
Washtenaw County 212
Kent County 78
Oakland County 62
Isabella County 53
Jackson County 45
Eaton County 32
Kalamazoo County 32
Livingston County 30
Calhoun County 27
Genesee County 25
Clinton County 24
59 other counties 390

The complete county distribution, spread across 71 Michigan counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

Big brown bat records in Michigan run from Ottawa National Forest in the Upper Peninsula to Shiawassee and Detroit River national wildlife refuges in the south, spanning nearly the length of the state. The species’ tolerance for buildings, bridges, and bat boxes alongside natural roosts explains why its reporting sites are spread so widely.

GBIF’s 1,144 records outnumber iNaturalist’s 221 by more than five to one, a gap that likely reflects hibernacula counts and specimen surveys rather than casual sightings. Reports peak June through August as maternity colonies become active; NatureServe still ranks the species S5, Secure, in Michigan, one of the few bats here not flagged by white-nose syndrome declines.

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 Michigan 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"