There’s nothing like winter to get us excited about hot chocolate, sitting by a fire, baking comfort food and bundling up in cozy layers.
Given the choice, most of us choose to spend the harshest and most brutal winter days inside. Animals, though, don’t exactly have a choice. Some animals, such as moles, groundhogs, badgers, some rabbits and some foxes burrow in the winter. But others have developed incredible physiological adaptations to help them weather the extreme cold.
Here are nine examples of noteworthy animal efforts at getting through winter.
Wood Frogs Freeze Solid Until Spring
The common frog often winters in the mud at the bottom of ponds. While buried, they breathe via the exchange of gasses through their skin, and they burn very little internal fuel.
But the hardy wood frog is slightly more dramatic.
Wood frogs are the only frogs that live north of the Arctic Circle, although “living” is a strong word for how they spend most of their days. They aren’t great diggers, so when the cold comes, they bed down in leaves or logs or loose ground.
Then, they freeze solid for up to eight months. As in…solid. First, ice takes over their abdominal cavity and encases their organs. Next, their brain freezes. Then, finally, their heart. They stop breathing completely and can even form ice crystals in their blood. Yet, somehow, when spring comes around, they dethaw and act like nothing ever happened.
How? It all comes down to sugar. In the fall, wood frogs go on an intense eating binge, gobbling up everything from moths to ants to put on weight. But they don’t put it on as fat; instead, they store it as glycogen. A high concentration of glucose in a wood frog’s vital organs stops them from being damaged.
Ken Storey, a professor at Carleton University in Canada who studies freeze tolerance, explains it like this:
“Water outside of the cells is frozen, and it leaves behind really concentrated goop. Inside the cells, there is never ice … All the cells are shrunken down, and what is inside the cell is a huge amount of sugar and a little bit of water left bound to sugar, not ice.”
Sound like a nice way to spend a season? Don’t get any ideas. If we made as much sugar as a wood frog does, we would die. To put it into perspective, even after we had made enough sugar to slip into a diabetic coma, we’d still need to make 20 times more!
Snails Cover Themselves With a Blanket
Who doesn’t like to snuggle into a warm blanket? Well, maybe not this particular blanket…
When snails are ready for a long winter’s nap, they attach themselves securely to something (a rock, a branch, etc.) before tucking themselves into their shell and closing up the hole with a thick blanket of their own slime. This not only keeps the elements out, but it also keeps critical moisture in.
During this time, they expend almost no energy and don’t have to eat anything at all. In some areas where there is very little rain, snails can happily turn a cozy siesta into a years-long hibernation!
The Common Poorwill Picks a Spot and Sleeps All Winter
Common poorwills are small, owl-esque nocturnal birds belonging to the nightjar family. They’re also the only birds known to hibernate. Hopi Native Americans even called the bird “the sleeping one.” A poorwill will usually conceal itself in a shallow pile of rocks or rotten logs and just check out for most of winter after consuming excess amounts of insects in the autumn to put on some extra body fat.
During hibernation, the poorwill’s temperature can drop to as low as 41 degrees, and their rate of respiration is reduced up to 90%, allowing them to stay asleep for up to 100 days straight. Once hibernation is over, it needs a snooze button of about seven hours to get back up to its normal temperature so it can go about its business again.
Dormice Won’t Be Outdone When It Comes to Snoozing
The dormouse looks at the common poorwill sleeping for 100 days and call them amateurs. Dormice hold the record for the longest hibernators: up to 11 months! In fact, they are so good at sleeping that their name is derived from the French word dormir, meaning ‘sleep.’
In late fall, dormice come down from the shrub layer (where they’ll have spent their active summer months) and build a small round nest on the ground. Then, theyy seal themselves in and go into hibernation. In 2012–13, a year when there was a shortage of their favorite food, beech mast, some adult female dormice were inactive for a whopping 346 days out of the year! They’re all typically wide awake and active by May.
Interestingly, dormice hibernate in quite exposed locations on the ground because it helps them to stay colder, helping keep them in hibernation. (In captive breeders’ cages, dormice always choose to hibernate in exposed, uncovered soil as opposed to soil that’s covered by a roof.)
Fat-Tailed Dwarf Lemurs Are So Accustomed to Heat They Start Hibernating at 82 Degrees
Fat-tailed dwarf lemurs, the only tropical primate known to hibernate, live in Madagascar, where “winter” temperatures in June and July drop to around 82 degrees F. While that sounds like lovely weather to us, it’s by far the coldest time of the year for the lemurs.
When the temperature drops, the lemurs choose a tree and settle there for about seven months until the rains return in November and food is available for them again. During their hibernation, they lose approximately 50% of their body weight and live off the fat in their tail (hence, the “fat-tailed” lemur). A lemur’s tail can account for up to 40% of its body weight.
Unlike animals that hibernate in temperate regions, the lemur doesn’t control its body temperature while hibernating. If the tree it chooses isn’t well insulated, its body temperature can be impacted by the outside temperature. It seems that the lemur uses hibernation not so much to escape the “cold,” but to survive the drought months.
As primates, these creatures are some of our closest living relatives, and scientists believe that we can learn a lot from the lemurs when it comes to better understanding human metabolism. When humans lie still, our muscles begin to atrophy and blood clots start to form. Yet, hibernating primates don’t have this issue.
Figuring out human hibernation could have powerful medical potential for trauma victims with significant physical injuries. Some scientists even think it could be the key to making very deep-space travel possible someday. If so, we may just have a funky little lemur from Madagascar to thank for helping us figure out how to hibernate effectively!
Black Bears Recycle Their Urine to Maintain Their Strength
During five months of inactivity during hibernation, a black bear loses only about 25% of its strength. For perspective, in three or four months of not moving, a human would lose a very dire 60%. How do bears manage this?
Hank Harlow, a professor at the University of Wyoming, spent much of his career tracking bears to their dens in and around Yellowstone. He measured body fat and muscle mass first in the middle of summer, then early in hibernation, and again five months later. What he and other researchers found is that bears don’t urinate while they hibernate, which means that they are not losing nitrogen. Instead, they’re recycling it into their blood, intestines and liver. The liver is where they make the amino acids, and then the skeletal muscle is resynthesized.
This also helps the bears to quickly heal injuries. Even major injuries that happened prior to hibernation are often completely resolved in one to two months.
Monarch Butterflies Vacation in Mexico
Every fall, tens of millions of monarch butterflies take off on a very ambitious 3,000-mile journey from the northeastern U.S. and Canada to their sunny wintering grounds in the volcanic mountains of central Mexico. Even though most generations live only four or five weeks, these traveling monarchs can live up to seven or eight months out of necessity.
The monarchs know the exact path to travel even though they have not migrated before, and once they make it to Mexico, they cling to the trees together in massive clusters to stay warm. When the Mexican sun warms their paper-thin wings, they become so active that you can hear their wings beating. By the time they arrive, they are nearing the end of their annual life cycle. They arrive, lay eggs, and it’s their babies that will continue the cycle back north for the warmer months. Although tiny, the young monarchs can cover about 100 miles per day!
Runner-Up for Chasing Endless Summer: The Alpine Swift
They may breed in mountains from southern Europe to the Himalaya, but when cold weather even thinks of coming around, alpine swifts are, well, swift to depart, heading straight to toasty Southern Africa. They can stay airborne for up to 10 months out of the year, constantly flying easily through warm air currents.
And the Winner for Actually Thriving in Cold Weather Goes to…the Arctic Fox!
While other animals figure out how to simply survive the cold, Arctic foxes are sub-zero specialists, able to withstand temperatures as low as -50 degrees. Their compact body, stubby little legs and small ears reduce exposure and conserve heat. They even turn more white in the winter months to blend into their snowy environment in the Arctic or Canadian or Eurasian tundra. They are the only canines to change coat color from summer to winter.
The Arctic fox’s thick fur coat and bushy tail keep them warm, but it’s their feet that allow them to move on top of ice and snow drifts without problem. Their wide, furry paws (much like those of the Canada lynx) are filled with polyunsaturated fats that don’t harden at extremely low temperatures, and unique membranes also help prevent tissue damage, two adaptations that work together to prevent frostbite.
They also have a counter-current vascular heat exchanger. In humans, blood from our heart is pumped throughout the body, circulating through the ends of your fingertips and toes before making its way back to your heart. When your feet or hands are cold, that cool blood circulates back through your feet and legs and insides to your heart, eventually cooling your body. But in an Arctic fox, the arteries and veins carrying blood down to their feet and back up to their core are quite close together, so heat from the blood actually warms the returning blood before it ever gets a chance to cool the body’s core. A constantly functioning internal heater!
How do you respond to cold weather? Do you fully embrace it like an Arctic fox? If so, consider one of our Antarctic or Arctic adventures and hang out with some cold-happy penguins, polar bears and Arctic foxes.
Or are you more like the monarchs and alpine swift, wanting to escape the cold? Maybe dodge the low temps with a balmy trip to Asia or the Pacific, Central America, a warm African safari or a sunny Galapagos getaway.
