Connecticut mammals

Big Brown Bat in Connecticut

Eptesicus fuscus

Native to Connecticut S5 Secure in Connecticut

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

Common in Connecticut 22nd most recorded of 70 mammals logged in Connecticut

215 occurrence records
104 with iNaturalist photos
Jul 2, 2026 Last seen in Connecticut

Records from 2000–2026.

215 total records count every Connecticut occurrence from GBIF and iNaturalist; the monthly chart covers the 195 records with a full observation date.

When to look for the Big Brown Bat in Connecticut

Most sightings fall in August.

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

Monthly Connecticut records (table)
MonthRecords
January4
February5
March12
April8
May14
June39
July31
August52
September13
October5
November6
December6

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

Seasonality

Year-round in Connecticut, with recorded sightings peaking in August, with a smaller rise in June.

Occurrence map

Where Big Brown Bat has been recorded in Connecticut

215 records mapped · zoom and drag to explore

215 Connecticut records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
Meshomasic State Forest And Gay City State Park 1
Old Newgate Prison And Copper Mine 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 Connecticut

CountyRecords
New Haven County 59
Litchfield County 28
Hartford County 27
Windham County 26
Fairfield County 23
Middlesex County 21
Tolland County 19
New London County 8
Other localities 4

The complete county distribution, spread across 8 Connecticut 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 among Connecticut’s most adaptable bats, roosting in buildings as well as tree cavities and feeding over ponds, clearings, and forest edges. Sleeping Giant, Hammonasset, and Bluff Point offer open flyways beside wooded roosting habitat. Visual identification in flight is unreliable; confirmed records often depend on close examination or acoustic surveys.

Reports peak in July and August, when warm evenings bring sustained insect activity and young bats join adults on the wing. Watch silhouettes over water after sunset, but never handle a grounded bat; keep people and pets away and contact a wildlife professional.

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 Connecticut in the atlas

Data & sources

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