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40 Below? Bring In Your Polar Bear, But Don't Worry About the Bats

By Rebecca Boyle
1/7/2014 9:33:27 AM

Sunday afternoon, I curled up with a blanket, a dog and a mug of tea and watched a foot of snow fall, while reading about the incursion of the epic polar vortex. We humans know enough, most of the time, to stay indoors when it's this horrible out - but what about the poor chilly animals? They know to stay inside, too (as it were). For hibernating mammals like bats, frigid temperatures are ... kinda no big deal.

Cave-dwelling bats shut themselves down for winter while there are no insects for them to eat, entering a deep state of hibernation. They find cold spots within caves or abandoned mines, and they cluster together in areas where temperatures don't fluctuate much, explains DeeAnn Reeder, a bat biologist and mammalogy expert at Bucknell University. "Those deeper parts where they're hibernating are not going to be subject to the temperature fluctuations that we would experience," she reassures me. "They're really tucked deep into these caves or mines, in areas that are stable year-round, so it's just not an issue for them."

Healthy Hibernating Little Brown Bats Ann Froschauer/USFWS

Problems arise when the bats rouse from their torpor. If they're near a cave entrance and decide to fly around, either because they were bothered or because they awoke hungry, they can get caught in the cold and freeze. In Toronto over the weekend, about 50 big brown bats were found outside a mall in -19 C temperatures (that's about -2 F), and six bats froze to death before a wildlife rescue group recovered them.

Big browns are often the last bats to enter hibernation, according to Reeder. They choose barns and attics and often go looking for a backup hibernation spot (a hibernaculum) after they're inevitably disturbed. Reeder calls them "superbats" because they're so hardy - but for those Toronto bats, it was just too cold.

Polar bears snuggling for warmth. (Credit: Flickr/Sue Hasker)

Today's coldest measurement in the U.S. was -36 (that's without wind chill) in Crane Lake, Minn. It is not a good idea for any mammal to be outside in those temps - even at zoos. Many zoos closed today and kept their animals indoors. Chicago's Lincoln Park Zoo was open, as it is every day, but the -40 F wind chill was too much for the polar bear and Bactrian camels, according to public relations director Sharon Dewar.

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