Most bats in North America hibernate, but “hibernate” for a bat does not mean the same thing it means for a bear. Bats drop into a state called torpor, where their body temperature falls, their heart slows way down, and they burn almost no energy. Some bats do this nightly, and some do it for months. A few skip hibernation entirely and fly south for the winter instead. Here is how it actually works, and why it matters if you are dealing with bats around your house.
Torpor versus hibernation
Think of it as two versions of the same trick:
- Daily torpor is short. A bat cools down for a few hours or a few days during a cold snap, then warms back up.
- Seasonal hibernation is the long version. A bat finds a protected spot and stays in torpor for weeks or months at a time, waking up only occasionally.
During either one, the bat’s heart rate and body temperature drop a lot, which is how it survives stretches with no insects to eat. The exact numbers vary by species and by how cold the roost gets, so I will not pretend there is one magic figure. The point is: they slow down dramatically.
Which bats hibernate and which migrate
- Deep hibernators: big brown bats, little brown bats, tricolored bats, and Indiana bats. These spend the winter in caves and mines.
- Partial hibernators: evening bats, red bats, and hoary bats. These may use daily torpor through cold snaps and sometimes shift short distances instead.
- Migrators: Mexican free-tailed bats, which head south to warmer weather rather than sticking around.
Do bats hibernate in attics?
Usually not for the deep, months-long kind. Most bats want a cave or mine, where the temperature and humidity stay stable. An attic swings too much in temperature and is too dry.
What you do get in an attic is daily torpor. If your attic stays mild through the winter, bats may use it to ride out cold spells instead of leaving for a cave. This is more common in warmer climates.
If you find a bat in winter
A bat that is up and moving around in winter is often sick, injured, or starving. Treat it as a possible rabies risk and do not handle it. Close off the room, open a window if you can, and call your local health department or a wildlife rehabilitator if it was in your living space.
Can you exclude bats in winter?
It is possible but trickier. Bats in deep torpor may not leave through a one-way valve, so an exclusion can stall. Sealing is fine if you have confirmed the roost is empty. The cleaner time to do bat exclusion is spring, after hibernation and before the females raise their young. Disturbing a hibernating bat makes it burn fat it needs to survive the winter, so if you suspect bats are holed up, the safest move is usually to wait for spring.
Frequently Asked Questions
They use daily torpor, cooling down and slowing their metabolism for hours at a time, or they migrate to somewhere insects are still around.
Most bat houses are too small and too exposed to hold a stable winter temperature, so they are not great for hibernation. Bats may use them for daily torpor in mild weather.
Yes. If a roosting bat gets hit with a sudden hard freeze and has nowhere insulated to go, it can die. That is why a good bat house in a cold climate should face the winter sun.
Put up a well-placed bat house, leave known hibernation sites like caves and mines alone, and support the groups that protect them.
