Massachusetts mammals

Big Brown Bat in Massachusetts

Eptesicus fuscus

Native to Massachusetts S4 Apparently Secure in Massachusetts

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

Occasional in Massachusetts 34th most recorded of 93 mammals logged in Massachusetts

263 occurrence records
261 with iNaturalist photos
May 25, 2026 Last seen in Massachusetts

Records from 2000–2026.

263 total records count every Massachusetts occurrence from GBIF and iNaturalist; the map plots a georeferenced sample of 255; the monthly chart covers the 255 records with a full observation date.

When to look for the Big Brown Bat in Massachusetts

Most sightings fall in May.

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

Monthly Massachusetts records (table)
MonthRecords
January8
February6
March15
April25
May60
June22
July36
August41
September13
October13
November9
December7

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

Seasonality

Year-round in Massachusetts, with recorded sightings peaking in May, with a smaller rise in July–August.

Occurrence map

Where Big Brown Bat has been recorded in Massachusetts

255 records mapped · zoom and drag to explore

246 Massachusetts records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
Mystic Lakes 2
Franklin Park Zoo 1
Cape Cod National Seashore 1
Burrage Pond Wildlife Management Area 1
Ponkapoag Pond 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 Massachusetts

CountyRecords
Middlesex County 91
Hampshire County 26
Worcester County 24
Suffolk County 20
Essex County 15
Plymouth County 14
Norfolk County 14
Franklin County 11
Hampden County 10
Berkshire County 8
Bristol County 6
Barnstable County 4
Other localities 20

The complete county distribution, spread across 12 Massachusetts counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

Big brown bats are one of the few Massachusetts bats that regularly roost in buildings, so a report from Oxbow National Wildlife Refuge or the wetland woods at Great Meadows National Wildlife Refuge is just as likely to trace back to an attic or barn nearby as to a hollow tree. That flexibility has helped the species hold up better than the state’s cave-hibernating bats, which white-nose syndrome hit far harder.

Records carry two peaks, a sharp one in May and a second in July and August, tracking spring emergence from hibernation and the summer maternity season when females and pups are most active on the wing. NatureServe ranks the species S4, apparently secure, one of the healthier bat statuses in a state where several relatives now sit at critically imperiled.

Occurrence data from iNaturalist and GBIF.

More mammals in Massachusetts 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"