This story was originally published in January 2013.
Frozen trees creak and snap. Icy branches clack together.
These are the sounds that can be heard while snowshoeing in the Maine woods. They’re small sounds — snow hitting the ground with a muffled thump, the trill of a chickadee. They’re the type of sounds that point out the silence of a snowy world.
What happened to the chatter and chirps that filled the same woods during the summer? How do the animals weather snowstorms and subzero nights?
“If you look, you’ll find all kinds of signs of animals,” said John DePue, wildlife biologist for the Maine Department of Inland Fisheries and Wildlife. “[Winter] is the best time for that. You’ll see squirrel tracks, coyotes, foxes, mink tracks and otter tracks along the water, snowshoe hare tracks, rabbit tracks — most of our animals don’t hibernate.”
For many animals, appropriate shelter, often with stashed supplies, is key for survival.
Small mammals, such as mice, spend most of their time tunneling through snow, said DePue. Insulated by snow, these tunnels are warmer than the open air.
Beavers spend much of the winter in “lodges” constructed of sticks and mud, feeding on the bark of small trees they stashed underwater during warmer months. Trappers can often tell if a beaver lodge is occupied by simply placing a bare hand over an air vent, said John Meister, a trapper from Old Town. If the warm air is escaping, beavers are home.
Sometimes, surviving the winter means banding together to stay warm. For example, the common grey squirrel is solitary in the summer, but in the winter, they usually bite the bullet and den up with fellow squirrels, according to the “Mammals of North America” Peterson Field Guide.
But simply being cooped up in a burrow isn’t the same as hibernating.
“Hibernation is basically when the animal has decreased respiration and decreased heart rate. You can’t wake an animal up from a hibernation state. It’s a state of suspended animation,” said Lisa Kane, wildlife educator of the DIF&W.
According to Kane, only three Maine mammals are considered to be “true hibernators”: woodchucks, jumping meadow mice and bats, which flock to hibernation caves called “hibernacula” in the fall.
What about bears, the animal most people think of as the ultimate hibernator?
Black bears are what biologists call “part-time sleepers.”
“It’s just a very general misconception,” Kane said of bear hibernation. “You can wake up a bear. When all of our bear biologists go into their dens in the winter, mamma bear is wide awake … They don’t eat or drink, but they don’t go into that deep state of torpor. They get up and move around.”
Other part-time sleepers are raccoons, porcupine and skunks.
“Then we have our stay-awakers — these are very technical terms — they’re mostly our predators — the fisher, the fox, the coyote and bobcat. They stay awake all winter long and hunt for things to eat,” Kane said.
Many of these predators have developed a way of walking called “perfect stride,” in which their back feet land in the prints of their front feet, decreasing the energy the animal spends breaking through snow.
Some of the most common tracks to see in the winter are those of nonpredator “stay-awakers” such as white-tailed deer, snowshoe hares and rabbits. Yet the forest often seems eerily still and quiet, as if the animals that left the tracks have become invisible.
Sometimes the hammering of a woodpecker or the flutter of a nuthatch can be heard, or the movement of a turkey picking through the snowdrifts or an eagle soaring overhead can be seen. While many of our birds have flown south, several species stay and brave the cold.
“Our earliest nesting bird is the great horned owl,” said Kane. “The courtship and nest building will start near the end of this month, and they’ll have their young by the middle of February. By the beginning of March, the young will be screaming for food. People describe it as it sounding as if someone is being murdered in the middle of the forest.”
Aside from birds, Maine’s major noisemakers are frogs.
In elementary school, children are told that frogs and turtles bury themselves in mud at the bottom of ponds and streams in the winter, only to reemerge in the spring. But it isn’t easily understood how that’s actually possible — How do they breathe?
As it turns out, the answer is not that simple.
According to a story in the Scientific American by Rick Emmer, lead keeper of The Rainforest at Cleveland Metroparks Zoo, turtles do make their winter bed in the muck. While hibernating, the turtle’s metabolism is slow enough for it to survive on the small supply of oxygen in mud.
Aquatic frogs, such as Maine’s noisy bullfrog, would suffocate.
Frogs make sure to keep some of their body out of the muck so they can have access to oxygen-rich water, according to Emmer. They may even slowly swim around from time to time. So, if you look down through a thin layer of ice and see a frog creeping around in the freezing water, don’t feel bad for it. It has air. It’s just changing sleeping positions.
Maine’s terrestrial frogs, such as toads and spring peepers, wait out the winter on land. Toads burrow into the soil below frost line, but wood frogs such as the peeper aren’t so good at digging, so they simply find a nook or cranny in which to hibernate.
Often, a wood frog’s body will actually freeze. Ice crystals will form under its skin; it will stop breathing and its heart will even stop. But it’s not dead. Why? A high concentration of glucose in the frog’s vital organs prevents freezing. When the spring rolls around, the frog thaws and its heart and lungs resume activity.
In addition to seeing many frogs on summer hikes, a number of garter snakes can usually be found basking in the sun beside the trail. And since these snakes live for a number of years, where do they go in the winter? They certainly don’t slither south.
According to the National Audubon Society “Field Guide to Reptiles and Amphibians,” garter snakes living in northern regions hibernate in community dens, often under large rocks or inside mammal burrows. These particular snakes are so good at tolerating the cold that they typically emerge early in the spring and have even been seen traveling over the melting snow.
What is the lesson learned from animal encyclopedias and biologists? People may be the loudest creatures in the forest, crunching down snow with plastic and metal snowshoes, but they are far from alone.