Eptesicus fuscus
Silhouette: Margot Michaud · PhyloPic
In 3 days ~30% in a week ~60%
The big brown bat (Eptesicus fuscus) is a species of vesper bat distributed widely throughout North America, the Caribbean, and the northern portion of South America. It was first described as a species in 1796. Compared to other microbats, the big brown bat is relatively large, weighing 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).
Big brown bats are insectivorous, consuming a diverse array of insects, particularly night-flying insects, but especially beetles. Some of the beetles it consumes are serious agricultural pests, including cucumber beetles. They are nocturnal, foraging for prey at night and roosting in sheltered areas during the day such as caves, tunnels, tree cavities, and human structures. Their breeding season is in the fall, shortly before their annual hibernation. After hibernation ends in the spring, females form maternity colonies for giving birth to young. Oftentimes only one offspring is produced per litter, though twins are common in the Eastern US. Lifespans of 6.5 years are considered average.
The big brown bat occurs widely throughout the US, Canada, Central America, and the Caribbean. Its range extends into parts of South America, found as far south as Colombia and Venezuela. It is adaptable to many habitats and is considered a generalist species. The big brown bat is not considered at risk for extinction, and is evaluated as the lowest conservation priority by the International Union for Conservation of Nature (IUCN).
While some other bat species in its range have experienced dramatic population declines due to the fungal disease white-nose syndrome, the big brown bat is relatively resistant to the effects of the disease, and some populations have even increased since the syndrome arrived in North America. Like all bats in the US, the big brown bat can be impacted by rabies, though some individuals have immunity against the virus. Even though sick bats are more likely to be submitted for testing, in 2011, only 3.8% of submitted big brown bats were positive for the rabies virus. Bat boxes are sometimes used to attract them as they are an agriculturally valuable species. Wikipedia →
Recording0:01
United States · 2025
© arkaen · iNaturalist · CC BY-NC 4.0
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United States · 2021
© nikkietorres · iNaturalist · CC BY-NC 4.0
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United States · 2026
© Lily Hendricks · iNaturalist · CC BY-NC 4.0
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Point Pelee National Park | 🇨🇦 Canada | |
| 2 | Great Smoky Mountains National Park | 🇺🇸 United States | |
| 3 | Saguaro National Park | 🇺🇸 United States |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Boston | 🇺🇸 United States | |
| 2 | Baltimore | 🇺🇸 United States | |
| 3 | Salt Lake City | 🇺🇸 United States | |
| 4 | Minneapolis [Saint Paul] | 🇺🇸 United States | |
| 5 | Denver | 🇺🇸 United States | |
| 6 | Montreal | 🇨🇦 Canada | |
| 7 | Washington | 🇺🇸 United States | |
| 8 | Toronto | 🇨🇦 Canada | |
| 9 | Philadelphia | 🇺🇸 United States | |
| 10 | Austin | 🇺🇸 United States |
| # | Zoo / Centre | Country | |
|---|---|---|---|
| 1 | Pittsburgh Zoo & Aquarium | 🇺🇸 United States | |
| 2 | Ralph Perkins II Wildlife Center and Woods Garden | 🇺🇸 United States |
With luck
About 10% of wildlife watchers report a Big Brown Bat sighting in Point Pelee National Park on a given day, based on 13 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 12th most-seen of the 17 mammals we can rate there. Over three days the chance rises to about 30%, and over a week to about 60%, if each day is a fresh chance.
September
In that month about 20% of wildlife watchers report a Big Brown Bat in Point Pelee National Park on a given day, against under 5% in June and October–April, the lowest months.
Between 10 am and 1 pm
Across all the parks we cover, that three-hour window holds the most Big Brown Bat sightings with a recorded time, and about 7 in 10 of them come between 6 am and 6 pm: it is seen both by day and at night.
Yes
Of the 3 parks where we can rate Big Brown Bat sightings, Point Pelee National Park has the highest daily chance: about 10%. Next come Great Smoky Mountains National Park (United States, about 10%) and Saguaro National Park (United States, under 5%).
Same family: Vespertilionidae
The closest relatives of the Big Brown Bat that you can see in Point Pelee National Park (family Vespertilionidae, Evening Bats) are Eastern Red Bat (about 20%), Tricolored Bat (about 10%) and Silver-haired Bat (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Big Brown Bat is recorded against all the mammals logged in Point Pelee National Park (13 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
