Arctic Ground Squirrel Hibernation: The Mammal That Chills Below Freezing
Arctic ground squirrel hibernation breaks the rules. For seven to eight months a year, these Alaskan squirrels sleep underground, and their body temperature drops below the freezing point of water. They don't freeze. In spring, they wake up and carry on.
Quick Facts
- Species: Arctic ground squirrel (Urocitellus parryii)
- Hibernation: 7 to 8 months a year
- Lowest body temperature: About -2.9 C (27 F)
- Trick: Supercooling
- Known for: The only vertebrate known to survive below-freezing body temperatures
Below Freezing, But Not Frozen
In the late 1980s, Brian Barnes at the University of Alaska Fairbanks found that hibernating Arctic ground squirrels let their core body temperature fall below freezing. A 1989 study in Science recorded temperatures as low as about -2.9 C. Their body fluids stay liquid through supercooling: with no ice crystals to start freezing, the liquid stays liquid even below 0 C.
Fattening Up First
Summer is short in the Arctic. The National Park Service says these squirrels often double their body weight before hibernation.
Shivering in Their Sleep
Hibernation isn't one long nap. Every two to three weeks, the squirrels shiver for 12 to 15 hours, still asleep, to warm back up to a normal body temperature. Then they cool down again.
Why Do Scientists Study Them?
A body that can drop below freezing and recover without damage is a puzzle medicine would love to solve. Scientists study the squirrels' supercooling in the hope it could one day lead to medical advances.
Frequently Asked Questions
How cold does an Arctic ground squirrel get?
Its core body temperature can drop to about -2.9 C (27 F) during hibernation without freezing.
How long do Arctic ground squirrels hibernate?
About seven to eight months a year.
Why don't hibernating squirrels freeze?
Their body fluids supercool: with no ice nucleators, the liquid stays liquid below 0 C.
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For Squirrel Fans
Gift idea
A tiny ground squirrel that never needs to hibernate: Hansa ground squirrel plush (5.0 stars). See it on Amazon
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Sources
- National Park Service: Arctic Ground Squirrel: hibernation length, weight gain and shivering
- University of Alaska Fairbanks: Arctic Ground Squirrels Are Supercooled: Brian Barnes' discovery
- Barnes (1989), Science: Freeze Avoidance in a Mammal: Body Temperatures Below 0 C in an Arctic Hibernator: the measurements
- Wikipedia: Arctic Ground Squirrel: supercooling
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