Eptesicus fuscus
Silhouette: Margot Michaud · PhyloPic
In 3 days ~20% in a week ~40%
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 →
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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 Great Smoky Mountains National Park on a given day, based on 27 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 16th most-seen of the 27 mammals we can rate there. Over three days the chance rises to about 20%, and over a week to about 40%, if each day is a fresh chance.
March, June–July, September and November
In those months about 10% of wildlife watchers report a Big Brown Bat in Great Smoky Mountains National Park on a given day, against under 5% in April–May, August, October and December–February, 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.
Among the best
Of the 3 parks where we can rate Big Brown Bat sightings, Great Smoky Mountains National Park ranks 2nd at about 10%, level with the leaders once rounded. The best odds are in Point Pelee National Park (Canada, about 10%).
Same family: Vespertilionidae
The closest relatives of the Big Brown Bat that you can see in Great Smoky Mountains National Park (family Vespertilionidae, Evening Bats) are Eastern Red Bat (about 10%) and Tricolored 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 Great Smoky Mountains National Park (27 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.
