Humans make it through the winter by stocking up on comfort food and firing up the DVR.
But hibernation gets a lot more interesting in the animal kingdom, where frogs freeze solid and lemurs live off fat in their tail for months on end. (Learn which animal hibernates the longest.)
Here are some hibernators that are a lot more unexpected than the average bear.
When the mercury rises, these frogsicles simply thaw out and hop away. “The wood frog’s ability is second to none,” says Jon Costanzo, a biologist at Miami University of Ohio.
How do they do it?
Their secret is a natural antifreeze that prevents fatal ice crystals from forming inside the frogs’ cells when their hearts and breathing cease. (See beautiful pictures of winter wildlife.)
Costanzo’s recent research also suggests that not peeing helps the frogs survive. Levels of urea, the main chemical in urine, rise 50-fold during hibernation, and gut microbes convert that waste into cold-buffering nitrogen.
While its feathered friends fly south, the common poorwill of North America falls into a seasonal slumber that inspired the Hopi to name it hölchoko, or “the sleeping one.”
When their insect diet becomes scarce, poorwills wait out winter days in a completely inactive state that’s unique among birds. The animals lower their body temperatures to 41 degrees Fahrenheit and slash oxygen consumption by 90 percent.
“They sit on the ground, next to a prickly pear cactus, and they don’t move even when you pick them up,” says Mark Brigham, a biologist at the University of Regina in Saskatchewan. “My student built a shelter over them, and got birds to sit there and not move for 10 weeks.”
Brigham likens the birds’ lifestyle to that of hibernating bats, but they are far more exposed to danger—19th-century explorer Meriwether Lewis described stabbing one with a knife.
“They certainly are strange,” Brigham says. “Why poorwills do it and nobody else we know of does is a mystery.” (Read why Japanese bats make tiny igloos.)
North American ponds change drastically from summer to winter, so painted turtles follow suit.
When their favorite watering holes are covered by ice, these reptiles lower their body temperatures and slow their metabolism by 95 percent. But they still need some oxygen.
“These are animals that breathe with lungs and they cannot get [to the surface] for a breath of air for half their lives,” says Jacqueline Litzgus, an ecologist at Laurentian University in Ontario. “To me, that's mind-boggling.”
Instead, hibernating turtles get the limited oxygen they need through their butts in a process called cloacal respiration. The blood vessels around the cloaca—an all-purpose orifice found in many reptiles—are able to take up oxygen directly from the water.
The only known primate hibernator relies on its namesake tail to survive Madagascar’s seven-month dry season. Fat-tailed dwarf lemurs spend half the year in a state of torpor, living on tail fats stockpiled by pre-hibernation feasting.
Sequestered in hollow trees, the lemurs’ body temperature drops, their heart rates slow from 180 beats per minute to four, and they breathe only once every 10 to 15 minutes. (Read how hibernating bears keep warm.)
Sustaining long periods of torpor is tricky for mammals; the brain stops functioning at body temperatures below about 68 degrees Fahrenheit, sleep can't occur in an inactive brain, and long periods of sleep deprivation lead to death.
But “the dwarf lemur solves this problem,” says Peter Klopfer, a biologist at Duke University. “At intervals from a few days to a couple of weeks, it will raise its body temperature for a few hours just enough to let the brain function again.”
“At that time, [lemurs] get intense bouts of REM sleep for a few hours. That happens repeatedly over six or seven months.”
Tardigrades may be humble microscopic creatures, but when it comes to survival in a dormant state, they’re possibly the most impressive animals on Earth.
These so-called “water bears” can survive without food or water for 30 years thanks to cryptobiosis, during which they shed almost all water in their bodies and curl up into a dried ball. (Learn about a new species of water bear discovered in a parking lot.)
Tardigrades have been subjected to, and survived, temperatures up to 151 degrees Celsius, and as low as -272.8—extremes that don’t exist in nature.
Researchers have even blasted them with high doses of radiation and sent them into the vacuum of space and back, both of which they survived unscathed. In fact, water bears would likely survive every apocalyptic scenario we can dream up.
And you thought getting through the winter was tough.