Winter Survival Guide for Wildlife

Some animals that need to stay warm in cold water—including penguins, whales, seals, and polar bears—rely on a fat called blubber. Compared with ordinary fat, blubber is firmer and has more blood vessels running through it. In cold conditions, these vessels constrict, reducing blood flow and keeping more heat inside the body, says Khudyakov.

Sometimes the best way to conserve heat is to snuggle with friends! Penguins, snow monkeys, voles, and honeybees all huddle for warmth. When animals press tightly together, less of their bodies’ surface is exposed to air, so more heat stays inside.

Some animals need to stay warm in cold water. They include penguins, whales, seals, and polar bears. They rely on a fat called blubber. Compared with ordinary fat, blubber is firmer. It also has more blood vessels in it. When it’s cold, the vessels get narrower. Less blood flows through them. So more heat stays inside the body, says Khudyakov.

Sometimes the best way to stay warm is to snuggle with friends! Penguins do this. So do snow monkeys, voles, and honeybees. When animals press tightly together, less of their bodies’ surface is exposed to air. More heat stays inside.

Fish, reptiles, and amphibians can’t generate their own heat to maintain their body temperature the way mammals do. Instead, these ectotherms take on the temperature of their environment. When surrounding temperatures drop, so does their body temperature. This slows down their metabolism. They reduce food intake or stop eating entirely and become less active as they wait for warmer weather and more abundant food.

Perhaps the most amazing example of ectotherms embracing the cold is the wood frog of Alaska and Canada. Winters in that part of the world are among the harshest on Earth. How does the wood frog cope? It freezes!

This feat was discovered by accident. A Canadian scientist collected some wood frogs in early spring and accidentally left them in his car. Temperatures dipped below freezing overnight. In the morning, he found what looked like a bunch of dead frogs, frozen solid. “He set them aside in the lab, planning to deal with them later,” says Jim Staples, a biologist at Western University in Canada. “Then he came back to a bunch of frogs hopping around!”

More than half of the water in the wood frog’s body freezes—but not water in its cells. The frog concentrates sugar in its cells, which reduces the freezing point of the liquid inside. This way, the fluid doesn’t freeze, even as water between cells and in blood vessels turns to ice. In spring, the frog thaws and hops off, good as new.

Mammals generate heat to keep their bodies warm. Fish, reptiles, and amphibians can’t do that. These animals are ectotherms. They stay at the same temperature as their environment. When surrounding temperatures drop, so does their body temperature. Their metabolism slows down. They eat less or don’t eat at all. They become less active as they wait for warmer weather and more abundant food.

There’s an amazing example of an ectotherm in the cold. It’s the wood frog of Alaska and Canada. Winters in that part of the world are among the harshest on Earth. How does the wood frog cope? It freezes!

This feat was discovered by accident. It was early spring. A Canadian scientist collected some wood frogs. He accidentally left them in his car. Temperatures dipped below freezing overnight. In the morning, he opened his car. He saw what looked like dead frogs. They were frozen solid. “He set them aside in the lab, planning to deal with them later,” says Jim Staples. He’s a biologist at Western University in Canada. Then the scientist came back to a bunch of frogs hopping around! 

More than half of the water in the wood frog’s body freezes. But the water in its cells doesn’t. The frog concentrates sugar in its cells. That reduces the freezing point of the liquid inside. So the fluid doesn’t freeze. Meanwhile, the water between cells and in blood vessels turns to ice. In spring, the frog thaws. It hops off, good as new. 

As the weather cools, mammals need to burn more energy to keep their body temperature up. “When humans shiver to keep warm, it uses energy,” says Staples. “That’s usually no big deal, because we can come inside and have a sandwich. Animals like ground squirrels can’t do that.”

Instead, the squirrels, which are native to North America’s grasslands, spend the summer eating plants to fatten themselves up. Come fall, they curl up in their burrow and hibernate, remaining in their home all winter and conserving energy. During their long hibernation, ground squirrels repeatedly cycle in and out of a state of inactivity called torpor. In torpor, metabolism slows down, so their bodies use less energy. Their breathing and heart rate slow, and their body temperature drops. A hibernating arctic ground squirrel’s limbs can fall to -2.9°C (27°F)—the coldest temperature ever recorded in a living mammal.

When it’s cold, mammals have to keep their body temperature up. That means they burn more energy. “When humans shiver to keep warm, it uses energy,” says Staples. “That’s usually no big deal, because we can come inside and have a sandwich. Animals like ground squirrels can’t do that.”

Ground squirrels are native to North America’s grasslands. They spend the summer eating plants to fatten themselves up. In fall, they curl up in their burrow and hibernate. They remain in their home all winter and save energy. Their hibernation is long. During this time, the squirrels go in and out of a state of inactivity. It’s called torpor. In torpor, metabolism slows down. Their bodies use less energy. Their breathing and heart rate slow. And their body temperature drops. A hibernating arctic ground squirrel’s limbs can fall to -2.9°C (27°F). That’s the coldest temperature ever recorded in a living mammal.

Every few weeks during their hibernation, ground squirrels briefly come out of torpor. Their metabolism increases and their bodies warm up. “All small hibernators do this,” says Staples. Some, like chipmunks, snack on stored food during these warm breaks. But ground squirrels don’t eat or release waste during these periods. They spend much of the time sleeping! During torpor, the brain may be too cold to sleep properly. Warming up may help animals keep this organ healthy by catching up on sleep.

Ground squirrels are extreme hibernators, remaining home for several months and dipping to ultralow temperatures. Groundhogs, hedgehogs, bears, and some bats also hibernate to survive winter without food.

Every few weeks during hibernation, the squirrels come out of torpor. Their metabolism increases. And their bodies warm up. “All small hibernators do this,” says Staples. Some, like chipmunks, snack on stored food during these breaks. But ground squirrels don’t eat during these times. And they don’t release waste. Mostly, they sleep! During torpor, the brain may not be able to sleep well. Maybe it’s too cold. Warming up may help the animals keep their brain healthy. They have a chance to catch up on sleep. 

Ground squirrels are extreme hibernators. They stay home for several months. And they dip to very low temperatures. Groundhogs, hedgehogs, bears, and some bats also hibernate. It allows them to survive winter without food.