Two bats in a cellar in bat hibernation

Bat Hibernation 2022 – What to expect?

Would you like to hibernate for the winter? Bat hibernation lasts from late fall until springtime. Across the US, bats have been preparing over the last couple of months by seeking their hibernation spots. The bats have also been feeding more to build up their fat supply so that it will sustain them when they enter a torpid state.

A cave used for bat hibernation in Georgia

Bats in a torpid state – what does this mean?

What comes to mind when you think of hibernation? Perhaps you think of animals sleeping deeply for a long time. Bat hibernation is, in fact, far more complex. Bats go into periods of torpor, which is an incredible energy-saving state – doesn’t that sound good?! Their body temperature lowers, heart rate drops, and breathing slows dramatically so that the bat’s fat store can last until Spring. Take the little brown bat, for example. Usually, when in flight, the little brown bat’s heartbeat could be around 1,365 bpm, and its resting heartbeat could be approximately 210 bpm when the surrounding temperature is 95 F. During hibernation, the surrounding temperature is much lower, and the bat’s heartbeat can slow right down to 20 bpm at a temperature of 44.5 F, what a huge difference!

A colony of hibernating bats in a cave

What happens if bat hibernation is disturbed? 

If bats are disturbed whilst in their torpid state, it costs them precious energy. It can take bats around 45 minutes to awaken from torpor. Being woken and returning to torpor will use 100mg of fat supply. The same amount of fat could last a bat in torpor for 67 days! If the bats are interrupted more than once, and especially if they are forced to fly out of the roost, their fat supplies will quickly diminish, which can be fatal.

Bat Hibernation fact file: 

The most common bats in the US are Little Brown Bats, Large Brown Bats, and Mexican Free-Tailed Bats. Although these bats sometimes inhabit the same areas, their hibernation habits differ. 

Little brown bat: 

  • Hibernation months: Little Brown Bats start hibernating in the North in September – October. In the South, hibernation starts a little later, in November. Hibernation ends around April – May.
  • Place: Little brown bats hibernate in colonies, which can number hundreds of thousands of bats. There are records of between 300,000- 500,000 large hibernation colonies. These are called “Hibernacula.” In the North American region, they are often found in humid caves or mines but may also choose buildings or tree/rock crevices. 
  • Distance traveled: Little brown bats may migrate hundreds of miles to reach their hibernaculum sites. One study actually recorded little bats migrating as far as 500 miles!
A little brown bat with its wings spread wide.

Large brown bat

  • Hibernation months: November / Early Dec – March. 
  • Place: Large Brown Bats can be found hibernating in caves, in rocky areas, in trees, and in man-made buildings. They are not usually found in large groups, but occasionally hibernation colonies of around 300 large brown bats have been found. Large Brown Bats may be found in hibernaculum alongside little brown bats – although they will usually be in a separate cluster. 
  • Distance traveled: Hibernation sites are not too far from their summer roosts – usually less than 50 miles away. 
A large brown bat clinging to a branch

Mexican Free-Tailed Bat

  • Hibernation months: None! That’s right, Mexican Free-Tails don’t hibernate. Instead, the majority migrate South. The largest number of Mexican free tails migrate from Texas to Mexico. Migration usually starts in late October or early November, depending on the weather patterns. When cold air arrives, this is the trigger for migration.  
  • Place: Similar to the little and large brown bats, Mexican Free-Tails can be found roosting in caves, rocks, trees, and man-made buildings.  
  • Distance traveled: Most Mexican Free-Tails make a long-haul flight of hundreds of miles. The longest known free-tail migration was around 1104 miles from North-Western Oklahoma to Mexico! They are proficient flyers, traveling at high speeds of + 50 mph, at an altitude of around 10,000 feet. These bats live in massive colonies and are known to travel en masse; millions of free tails have been seen landing at once! 
A Mexican free tailed bat clinging onto a tree

During the winter months, keep watch for signs of bats around your properties. If you think bats are hibernating in your residential or commercial property, contact your local bat removal specialist for help.

Your Local Bat Removal Expert,

Michael Koski

Get Bats Out Owner and President Michael Koski

Read More:

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