Identify Your Pest Wildlife Big brown bat
Big brown bat
Eptesicus fuscus
The big brown bat is a sturdy, glossy brown bat found mostly in central and southern Alberta, including Edmonton, Red Deer and Calgary. It can spend the winter inside buildings, so it is the bat most likely to turn up in a home in winter.
Size 10 to 13 cm long; wingspan up to about 35 cm
Colour Tan to chestnut fur, often glossy; black face, ears, wings
Key feature Stocky bat with a wide head and a blunt, puffy-looking muzzle
Season Mainly spring to fall; may hibernate in heated buildings
Where Attics, wall spaces, soffits and barns; heated buildings in winter
What it looks like
This is a sturdy bat, and among Alberta’s bats only the hoary bat is clearly bigger. Adults weigh roughly twice as much as a little brown bat, and the wings can span about 35 cm. The coat can be anything from light tan to rich chestnut and often looks oily. The face, ears and wings are black, and the muzzle is wide and blunt.
In summer, females gather in warm attics, walls and barns to raise their young. Big brown bats are hardy and can overwinter in a heated house, garage or other building. On mild winter days they may wake up and wander into living spaces, which is often how people find out they are there.
Often confused with
Little brown bat
Silver-haired bat
Signs to look for
A bat indoors in winter
Crumbly droppings
Bats leaving at dusk
Stains and smell
Scratching and squeaks
Risks and damage
Big brown bats are mostly a nuisance. Droppings and urine collect under roosts, stain surfaces and cause a musty smell. Bat droppings crumble into dust, so large piles should not be dry-swept. This is one of the bat species that has tested positive for rabies in Alberta, though the risk to people is very low. Anyone bitten, scratched or touched by a bat, or who wakes to find one in the room, should contact Health Link or a doctor.
In Alberta
In Alberta this bat lives mainly in the central and south of the province, so Edmonton, Red Deer and Calgary are in its range. Barns, farmyards and river valleys are typical haunts. No other Alberta bat is known to spend the winter inside buildings. It is protected, not endangered.
Big brown bats handle cold better than most bats. They can hibernate in colder, drier spots, which is why they are the bat most likely to spend the winter inside a building.
How to keep them out
Time the sealing
Screen vents and chimneys
Close indoor gaps
Offer a bat house
When it is time to bring in a professional
Call a professional if bats are roosting in your attic or walls, or if bats keep turning up inside in winter. Big brown bats may hibernate in the building, so exclusion must be carefully timed. Technica’s licensed technicians can find entry points, set up one-way exits at the right time of year and seal the building.
Frequently asked questions
Why is there a bat in my house in winter?
It is most likely a big brown bat that was hibernating in your attic or walls. A warm spell or heat from the house can wake it, and it may wander into a room. It is a sign bats may be using the building, so an inspection is worthwhile.
Should I put a bat outside in winter?
No. A bat released into the cold will likely die. Do not touch it with bare hands. If no one had contact with it, ask a wildlife rehabilitation centre for advice. If anyone may have been bitten or touched, contact Health Link or a doctor first.
Is the big brown bat endangered?
No. Unlike the little brown bat, it is not listed as endangered. It is still protected under Alberta’s Wildlife Act, so it must not be harmed or killed. Humane exclusion at the right time of year is the accepted approach.