Where Do Bats Go in Winter in Ontario?

In Ontario, bats either migrate south or stay put and hibernate. Some, like big brown bats, hibernate right inside heated attics and walls, while little brown bats prefer caves and abandoned mines. A warm attic can hold a torpid colony all winter — quiet for months, then stirring on a mild thaw.

If your attic went silent in November, it is tempting to think the bats packed up and left. Often they did not. They just went dormant. Understanding what bats actually do in an Ontario winter helps you avoid two common mistakes: assuming the problem solved itself, and trying to evict a colony at the worst possible time of year.

Do Ontario bats migrate or hibernate?

Ontario bats split into two broad groups when the cold sets in.

Some species are long-distance migrators. As insects disappear and nights turn frosty, they travel to warmer parts of the continent, then return in spring. For these bats, your building is a summer roost, not a winter home.

Other species stay in Ontario year-round and hibernate. They gather in sheltered, stable spots called hibernacula — places where the temperature stays cool but above freezing and the humidity stays high. Natural hibernacula include caves and old mines. The catch is that a heated house can accidentally offer the same thing: a dry, protected, steady-temperature space, tucked out of reach.

The two species most Ontario homeowners deal with behave very differently in winter, and telling them apart matters. Our guide to big brown vs little brown bats breaks down the differences in detail.

Which bats hibernate in attics?

Here is the key distinction. Not every bat that summers in your attic will winter there.

Behaviour	Little brown bat	Big brown bat
Preferred winter site	Caves, mines	Buildings, attics, walls — plus caves
Cold tolerance	Lower	Higher — handles cooler, drier spots
Likely to overwinter in your house?	Less often	Yes, commonly
Often leaves in fall for a hibernaculum?	More often	Sometimes stays put

Big brown bats are the species most likely to hibernate inside your home. They tolerate the drier, cooler conditions of a wall cavity or attic better than little brown bats do, and they will happily settle into a quiet corner for the season. Little brown bats more often move to a cave or mine to hibernate, though they are the classic summer attic tenant.

The practical takeaway: a summer bat problem does not always mean a winter one, but if you have big brown bats, there is a real chance the colony never left.

What is torpor, and why does it go so quiet?

When a bat hibernates, it does not simply sleep. It drops into torpor, a deep energy-saving state. Its body temperature falls close to the surrounding air, its heart rate slows dramatically, and its breathing becomes shallow and infrequent. The bat is running on the fat it stored up in late summer and fall, stretching that fuel across the whole winter.

In torpor, a bat barely moves. That is why an attic that buzzed with activity in August can go completely silent by December. The colony is still there — it is just powered down.

This is also why bats are so vulnerable in winter. Every time a bat rouses from torpor, it burns a chunk of its limited fat reserves. Too many unnecessary wake-ups and it can run out of fuel before spring. That single fact shapes everything about how a responsible company handles bats in the cold months.

Why do I hear bats on a warm winter day?

You go weeks without a sound, then a mild January thaw rolls through and suddenly you hear scratching, scrabbling, or fluttering overhead. What happened?

Warmth happened. When outdoor temperatures climb and the attic heats up, some hibernating bats naturally rouse from torpor. They may shift position, crawl around, drink, or even take a short flight. Occasionally one gets confused by the warmth, finds its way into a living space, and turns up in a bedroom or on a curtain.

This does not mean a new colony just arrived. It almost always means bats have been overwintering in your home the whole time, and a thaw briefly woke them. It is one of the clearest signs that the “problem” you thought disappeared in the fall is very much still present.

Can you remove bats from an attic in winter?

No — and this is the part people find surprising. Winter is not bat exclusion season.

Humane bat removal relies on a technique called exclusion. A technician seals every gap in the building except the active entry points, then fits those with a one-way door. Bats leave to feed at night, cannot get back in, and the colony empties out over several nights. Once everyone is out, the last openings are sealed. You can read more in our guide to exclusion versus removal.

The whole method depends on bats flying in and out. In winter, they are not doing that. A torpid colony is present but immobile, so a one-way door has nothing to let out. Worse, forcing bats out into freezing air — when they cannot find food, cannot rebuild their fat, and may not survive the cold — is neither humane nor effective.

There is also a timing rule that matters. You can only safely seal a home once you have confirmed the bats are out. Mid-winter, you can neither evict a dormant colony nor verify the building is empty. Sealing blind risks trapping live bats inside your walls, where they will die and cause odour and mess. So the honest answer is that winter exclusion should not be done.

What winter IS good for: inspection and planning

Winter is far from wasted time. It is the ideal season to get ahead of the problem.

• Book a free inspection. A licensed technician can confirm whether bats are actually present, identify the species, and gauge the size of the colony.
• Find every entry point. Bats can slip through a gap the width of your thumb. Winter inspections map the soffit gaps, roofline joints, chimney flashing, and vents that need attention.
• Plan the exclusion. With the entry points documented, we schedule the work for the correct window so it happens the moment the season opens.
• Prepare for cleanup. A winter’s worth of droppings (“guano”) builds up. Planning ahead means guano removal and sanitizing are ready to go alongside the sealing work.

Ontario’s practical exclusion window runs from mid-August through October, after the summer maternity season ends. From roughly May to early August, colonies contain flightless pups, and a one-way door would strand those pups inside to die while their mothers are locked out — so exclusion is never done then. Our post on maternity season and why timing matters explains that window in full.

That leaves two smart moves for a winter caller: line everything up now, or, if you are reading this closer to spring, get on the schedule early so the work lands the moment the window opens. Homeowners who plan bat-proofing before the cold — see our fall bat-proofing guide — often avoid the winter surprise altogether.

How do I keep bats out for good?

The lasting fix is sealing the building properly so no bat can find its way back in. Done right, exclusion is a permanent solution, not a yearly chore. Every soffit gap, loose flashing, and worn vent screen becomes a potential doorway, so thoroughness is everything. Our complete bat-proofing guide walks through what a fully sealed home looks like.

Is it dangerous to have bats hibernating in my house?

While bats are dormant, the everyday risk to your family is low — but there are real reasons not to leave them be.

Droppings accumulate all winter. Over time, guano can support a fungus linked to a lung illness called histoplasmosis, which is why cleanup should be handled with proper protection, not a shop vac and a dust mask. Bats are also a rabies-vector species in Ontario. The risk from an undisturbed bat in your attic is small, but you should never handle a bat with bare hands. If you think a person or pet may have been bitten, scratched, or exposed — including waking to a bat in the room — contact Health811 or your local public health unit for guidance.

None of this is cause for panic. It is simply why a hibernating colony is a problem to plan around, not one to ignore.

What will winter bat work cost?

There is no flat price, because no two houses are the same. The cost depends on the specifics — the number of entry points, the size and access of your roofline, the extent of the colony, and how much guano cleanup the attic needs. After we inspect, we give you a clear, honest quote up front and walk you through exactly what the job involves, so there are no surprises.

Ready to get ahead of it?

If your attic went quiet this fall, or you heard bats stir on the last warm day, do not wait for spring to find out what is really going on up there. Winter is the perfect time to book a free, no-obligation inspection through our bat removal and exclusion service page or right from the home page.

We are a family-run, licensed, local team serving Grey, Bruce, Simcoe and Huron counties, and every exclusion we complete is backed by our transferable Lifetime Warranty — if a bat ever gets back in through a point we sealed, we come back and fix it at no charge, for the life of the building — and the warranty transfers to the next owner. Let us confirm what is in your attic now, and have your exclusion scheduled for the moment the season opens.