By Taylor Smith | Photos courtesy of Shutterstock.com

Every year, the Earth undergoes changes in weather and seasons. Sometimes these are extreme (like eight months of biting winds in the taiga forests of Canada) or brief and subtle (a couple months of 50-to-60-degree temperatures in the southern U.S.).

Many animals react to these changes as a means of self-preservation. While the term hibernation is familiar to most, many would be surprised to learn that very few species actually sleep non-stop for the entire winter. Instead, most are experiencing torpor, a state of reduced physiological activity that includes lower metabolism, heart rate, respiration, and body temperature.

Unlike hibernation, torpor is involuntary and lasts for just a few hours during the daytime. Food availability and outside temperature both influence torpor. Animals in torpor can wake up quickly to avoid danger or to feed.

Many rodent and small mammal species practice this state. On any given day they will move between times of activity when their metabolism and heart rate are relatively normal and times of reduced physiological activity to conserve energy.

The hazel dormouse is an example of classic hibernation. Residing throughout much of Great Britain, they prefer to nest in the shrub layer on top of the ground from October through May.

The Mad Hatter’s Tea Party, illustration from “Alice’s Adventures in Wonderland” by Lewis Carroll. (Art by John Tenniel; Wikipedia)

The dormouse may be recognizable as the sleepy mouse character in Alice’s Adventures in Wonderland. In the story by Lewis Carroll, the Dormouse is seated at a tea party with the Mad Hatter and the March Hare. He is initially being used as a cushion while he continues to sleep.

Carroll writes, “You might as well just say, added the Dormouse, who seemed to be talking in his sleep, that “I breathe when I sleep” is the same thing as “I sleep when I breathe!”

Green frog under the ice of a pond.

Reptiles and amphibians undergo brumation, which is triggered by a drop in environmental temperatures. Snakes, lizards, and frogs are ectothermic, and their body temperature is dependent on the outdoor temperatures. As the sunlight decreases and the winter weather takes hold, reptiles will exert less energy, making it more difficult for them to hunt.

Garter snakes emerging from an underground den.

Common garter snakes are found throughout New Jersey and are also some of the first brumating reptiles to emerge in mid-March. Garter snakes typically retreat to an underground den (below the frost line) anytime between mid-September through November. They may share the den with other garter snakes for added warmth. These reptiles will appear inactive, but they are not totally asleep. If ice and deepening snow lower the outside temperatures, the snakes will move deeper underground. On the chance of winter sunshine, the snakes sometimes emerge to soak up the warmth.

So, how does hibernation work for a snail? When seasonal changes occur and food resources become scarce, snails will undergo hibernation that allows them to conserve their energy. During wintertime, snails retreat into their shells and close off the opening with a layer of dried mucus. Once inside their shells, snails experience a slowed metabolism, allowing them to wait out the harsh weather until food resources become readily available again.

Cold Weather Adaptation and the Threat of Climate Change

Some might not realize that many of the Earth’s animals that naturally go into a dormant state during the winter are perfectly adapted for cold weather. Yes, surviving each winter is a gamble for every bear, marmot, and dormouse, but these animals would be more at risk in a hot year-round environment. They are genetically fashioned to blend their fur coats into the winter white landscape. They know the indicators each year for when they should start loading up on calories, preparing a den, and stockpiling food.

Another threat from climate change is the possibility of animals becoming active too early. New Jersey’s chipmunks enter a state of torpor to survive the winter weather. If they perceived warming temperatures while still in the middle of winter, they could easily die from the frozen ground, lack of food source, and winter predators.

The Nature Conservancy’s New Jersey branch oversees one of the most populated states in the country. With such a dense human population comes the loss of animal habitat. Of New Jersey’s 800 estimated species, 80 of them are currently listed as endangered. Bog turtles hibernate every year and require wetlands to do so. Wetland habitat loss is a critical issue throughout the state. According to the Nature Conservancy of New Jersey, the primary reasons are “development, pollution, and invasive species.” Bog turtles are most active in the spring when they readily emerge from hibernation and look for a mate.

While bumblebee colonies do not hibernate, but in fact die-off every fall, the new queens will overwinter in small holes, nooks, and crannies in the ground’s surface. Central to the new colonies’ survival, the queens will emerge in the spring and begin laying huge quantities of eggs. If you would like to make your own backyard friendlier for queen bumblebees, you can create a log pile, build an open compost heap or a raised bed, and leave cut grass, dead leaves, and moss coverings in a dedicated pile. Queen bumblebees are relatively strong and use their legs to dig small holes. If you come across a queen bumblebee while doing some cold-weather yard work, immediately cover her back up and try not to bother her further. Unfortunately, many people do not understand the necessity of bumblebees within our global environment. For more information on bumblebee cultivation and education in New Jersey, visit the Nature Conservancy of New Jersey at nature.org/en-us/about-us/where-we-work/united-states/new-jersey.

Alaskan brown bear

The Fat Bear Contest

Every year, the National Park Service in Katmai National Park and Preserve in Alaska holds an amusing contest known as Fat Bear Week. For this year’s event, a brief biography, photos, and statistics of 11 brown bears can be found on fatbear.org, along with insights into each bear’s personality and behaviors. Voting is held each fall. The park rangers say, “Fat Bear Week is a celebration of success and survival. It is a way to celebrate the resilience, adaptability and strength of Katmai’s brown bears.”

Loading up on fat and added weight is significant for Alaska’s brown bears since they typically hibernate in the coldest regions of Alaska for seven months. In the southern, coastal regions of Alaska it might be two to five months of hibernation.

In the Katmai National Park and Preserve, bears may retreat to their den in October or November. These bears experience hormonal changes and a reduction in the availability of certain foods, which will cue them to retreat to their den. After a well-spent summer and early fall consuming food, hibernation will cause significant physiological changes, meaning that a bear will go months without food or water. They also will not urinate or defecate while in the den. In addition, as their body temperature drops, so will their respiratory and heart rates. By the time these animals emerge from their dens, their body weight will have decreased by around 33 percent. Oddly enough, they typically do not experience a drop in bone or muscle mass.

Princeton’s Ultimate Survivalists

When you think of Princeton, many think of black squirrels. A recessive gene variant of North American gray squirrels, these squirrels (and North American squirrels in general) are the ultimate survivalists because they continue foraging, working, and collecting throughout the winter season. On extremely frigid days, they will take to their nest and slumber without coming out. To prepare for such times, squirrels use the fall to hide and bury as many nuts, seeds, and pinecones as they can find. Thus, when winter comes, they will retrieve their buried treasure, treating the cold soil as their own personal freezer. Another winter adaptation is that squirrels typically share their nest with other squirrels, making their burrows quite a bit warmer.

Little brown bats

Most over-wintering bats in New Jersey experience torpor. As their body temperature and heart rate drop due to the environmental temperatures and lack of insect activity, these creatures will seek out caves or mines where they can be left undisturbed. Unfortunately, climate change and a warming Earth have increased the rate of white-nose fungus for bats. As described by the National Park Service on nps.gov, “Researchers call the disease white-nose syndrome (WNS) because of the visible white fungal growth on infected bats’ muzzles and wings. This cold-loving fungus infects bats during hibernation, when the bats reduce their metabolic rate and lower their body temperature to save energy over winter. Hibernating bats affected by WNS wake up to warm temperatures more frequently, which results in using up fat reserves and then starvation before spring arrives.” Identified by discolored white fungus on the face and nose, this disease can eliminate entire bat colonies over a short period of time.

While not everyone may be fond of bats, they do provide critical benefits to our planet. From crop and plant pollination to the consumption of disease-carrying mosquitos, bats are significant. Also, if you like tequila, remember that bats are chief pollinators of agave plants.

Groundhog

Other local animals that are master winter survivalists are groundhogs and skunks.

Contrary to what you may see in Puxatawney, Pa., each year, groundhogs prefer not to be woken up on February 2 to look for their own shadow in a Pennsylvania Dutch tradition that still draws crowds and national news networks. Groundhogs generally hibernate from late-October to early-March. Gifted with strong digging claws and a compact body, they weigh between 5 to 10 pounds. Groundhogs prefer to build their own network of underground dens and tunnels. True herbivores, they will eat all manner of vegetables, beans, peas, alfalfa, clover, and grasses.

Skunks enter a state of torpor in the winter in which they nap inside their burrows to escape extreme temperatures. Skunks do rely somewhat on their own fat storages to fuel them during the coldest days, but they will also forage for grubs and roots. Skunks emerge in February and March for mating season and deliver cubs in the spring. April and May are the most active time of year for skunks, making them highly visible to pets and homeowners.

While not especially common in New Jersey, badgers go underground and enter a deep state of rest during the winter months. Badgers are also nocturnal and if they do emerge from their dens (or “sets” as they are known), this will typically occur at dusk. With a reduced metabolism, heart rate, respiration, and body temperature, badgers will rarely leave their set if the temperature is below freezing.

Jeff Hoagland, education director at The Watershed Institute in Pennington, says, “Climate change is impacting the length of seasons, with the warm seasons growing in duration, in this location, starting earlier and ending later. Gardeners may be the most in tune with this, however, this phenomena has implications on the plants and animals in the wild. There is a change in the phenology, the cyclical sequence of seasonal natural phenomena, in all locations. In my time here at the Watershed (40 years), we have seen the sugar maple sap run, the arrival of woodcocks, and the emergence of spring peepers occur earlier in the year, for example. Scientists are studying the implications of these changes to individual species, and to ecosystems.”

All of this is good to keep in mind as you venture outside for a winter walk this year. Remember to think about all of the animals, insects and amphibians that are actively hibernating and brumating in the hopes of returning to their unique lives in the spring.

If you would like to encourage hibernation health in your backyard, refrain from using pesticides and insecticides, leave adequate roughage and shelter for animals to seal themselves away, and avoid any interactions between domestic pets and sleeping mammals.