Surviving Winter

Do I stay or do I go? And if I stay, do I just sleep through it all? The Southern Appalachians are home to a large and diverse fauna, and as winter sets in, that fauna gets to work surviving.

Groundhogs’ heart rates may drop from between 80 and 100 beats per minute to five. Their body temperature, normally around 98 degrees Fahrenheit may drop to as low as 40 degrees Fahrenheit. It generally stays at just a few degrees above the ambient (the temperature surrounding them) temperature in their burrow.

Painted turtles generally hatch in September or October but the babies don’t head for open water. “They will stay in their nests all winter, and they produce a natural kind of antifreeze that prevents their cells from freezing,” said Landon Ward an instructor at University of North Carolina Asheville’s Department of Environmental Studies. 

Honeybees cluster together in the hive using their collective body heat and food stored in the hive to make it through. On the other hand, bumblebees are basically done for except for a few queens that retreat deep into the nests and hibernate over winter. 

Perhaps the most obvious creatures to coalesce to the cold, are the birds—like kindly grandparents from Florida, they head south when the temperatures start to fall. The forests and fields across the Southern Appalachians empty and become quieter and more still. 

Simon Thompson, owner of Ventures Birding Tours and co-owner of Asheville Wild Birds Unlimited, said “a full 70 percent of the birds that nest in the forests of the Blue Ridge migrate.” These birds, known as neotropical migrants, nest in North America but spend their winters in Central and South America. That means that each fall, within a few short weeks, millions of birds vacate the Southern Blue Ridge. The brightly colored warblers, like chestnut-sided, black-throated blue, black-throated green, Canada, hooded and many, many more that danced and sang outside your tent at dawn every morning of your backpacking trip in the Smokies are gone. The scarlet tanager that blazed through the green treetops at your favorite overlook along the Blue Ridge Parkway—gone; the rose-breasted grosbeaks that stopped to pick black oil sunflower seeds from your backyard feeder—gone; the golden Baltimore orioles that nested at Beaver Lake Sanctuary in Asheville, N.C.—gone; the eastern kingbirds that patrolled fields and meadows hawking insects—gone; the raincrow (yellow-billed cuckoo) that called softly from the woods before every thunderstorm—gone; and that irrepressible iridescent indigo bunting that bounced around and sang from the clearing down by the lake—gone. 

How does that happen? How do millions of songbirds (passerines) up and leave and hardly anyone notice? They leave under the cover of darkness, literally. They migrate at night. Thompson noted a few reasons for that. “There are fewer predators at night, and many birds use the moon and stars to help them navigate,” he said. Nighttime also, generally, makes for a smoother ride because the atmosphere is more stable. It also appears to help the birds keep their cool. “Birds use an immense amount of energy during migration and migrating at night, at higher altitudes, where temperatures are cooler helps keep them from overheating,” Thompson said.

Now, all neotropical migrants aren’t fly-by-nights. Raptors (birds of prey) are diurnal migrants—they migrate during the day. And while songbirds migrate at night to avoid thermals (rising currents of warm air,) diurnal migrants seek them out. “Raptors utilize thermals and mountain updrafts to aid in migration—the idea is to use as little energy as possible,” Thompson said. Birds can soar on currents from thermals and/or updrafts for miles at a time never having to flap their wings. Broad-winged hawks are the only true neotropical raptor that nests in the Smokies and they have usually all disappeared by mid-October.

And not all migrants are neotropical migrants. Some birds move just far enough south to find ample food. For example we often wind up with more sharp-shinned and Cooper’s hawks in the winter months than we have in the summer. There is also an “elevational migration” in our mountains. High-elevation nesters like dark-eyed juncos, yellow-bellied sapsuckers, golden-crowned kinglets and others move down the mountains in the winter.

There are at least 50 species of birds that stay with us year-round. Some of these are Carolina chickadee, tufted titmouse, song sparrow, northern cardinal, eastern towhee, eastern bluebird, northern mockingbird and at least five species of woodpeckers. But even these residents show wintertime adaptations. Some add extra down-feathers during their fall molt to increase insulation. Others like robins and eastern bluebirds shift from an animal diet (insects and/or worms) to more berries and seeds. Groups of eastern bluebirds will roost together in the same cavity if it gets especially cold. Some birds like Carolina chickadees can slip into torpor—a state where their metabolism rate is greatly lowered and body temperatures are dropped—to conserve energy.

And birds aren’t the only creatures that fly away. While the mechanics and logistics are still uncertain, biologists are sure that a number of dragonfly species migrate in the fall. Some migrant dragonflies found in the region include green darner, wandering glider, black saddlebags, and spot-winged glider. These bugs head south in great swarms in the fall and it is known for sure that green darners and black saddlebags make it as far as Mexico.

But without a doubt the royalty when it comes to migrating insects is the monarch butterfly, King Billy. Early colonists dubbed monarch butterflies “King Billy” because the glistening orange color reminded them of William of Orange, King of England. Monarchs that routinely make it as far north as eastern Canada in the summer, turn, fly, waft and glide as far as 2,000 miles south to their primary wintering grounds in the Michoacán mountains of Mexico. One monarch tagged in Central Park on August 27, 2005, was recaptured at El Rosario Monarch Sanctuary on February 14, 2006, a trip of more than 2,100 miles. Monarch migration brings a steady stream through Western North Carolina from mid-September through mid-to late October. (While huge numbers of migrating monarchs are not common across the region, I do remember one early October day a few years back when a group of us, looking for migrating birds, encountered large swarms of monarchs at the Pink Beds along Highway 276 in the Pisgah National Forest. Monarchs were dancing in the breeze from the treetops to as high as we could see.) Migrating monarchs have been recorded at altitudes above 11,000 feet during migration.

And of course bugs are just like all other animals in the fact that they’re all different. Dragonflies, monarchs and some others may migrate but other insects employ different strategies to get through the winter. Some, many actually, don’t get through the winter. Insects have, relatively speaking, short lifespans—their primary evolutionary calling is to perpetuate the species and most adults die after breeding, but many overwinter as eggs (praying mantis) or larvae (woolly worms) or nymphs (mayflies, stoneflies) or pupae (pipevine swallowtail.) The adults that make it have different strategies. Mourning cloak butterflies may not be as sexy as King Billy, but they are usually the first butterflies to appear in the region in the spring because adults hibernate, often in tree cavities, over the winter.

Seasonal patterns reflect changes in required resources—food, water, habitat. Subtle clues such as the change in temperatures, photoperiodism (change in number of hours of daylight and dark) and even the tilt of the Earth’s axis that seem to alert animals to the fact that precautions must be taken. Before electricity, Henry Ford, assembly lines and factories, most people fell into those same kinds of circadian and seasonal rhythms—spring was a time of awakening, summer was a time of labor, fall was a time of harvest and winter was a time of rest, contemplation and preparation. 

When it comes to migration, herds of wildebeests and gazelles in Africa or pods of whales in the open ocean are likely most commonly known. The only mammal in the Smokies region that might be considered a migrant is the bat and that is murky waters. We have red bats here that migrate farther south and we have red bats that migrate here from farther north then hibernate. We also have lots of little brown, big brown and tri-colored bats (formerly eastern pipistrelle) that migrate here to hibernate in caves alongside resident bats. However, once here for the winter, bats in the region are mainly hibernators.

Hibernation is a fascinating winter-coping tool. Most warm-blooded animals (endotherms) that hibernate, like groundhogs and chipmunks, are able to slow their metabolism and lower their body temperature to just a fraction of what it was while they were last active. Dr. Lisa Muller, associate professor of Wildlife Management at the University of Tennessee, said that hibernation “…is really about how much food it takes to retain a body temperature that sustains life.” So if animals like chipmunks and groundhogs and other hibernators are able to drop their metabolic rate, “…that’s a good idea,” she said because that means less food (nourishment) is required to keep the animal alive.

One conundrum regarding hibernators in the Southern Appalachians is the black bear. Whereas critters like chipmunks (true hibernators) almost always have a stash of food in their den and have to awaken periodically to go to the bathroom and have a midnight snack—black bears generally never eat nor urinate nor defecate during their entire “big sleep.” Plus, while the bear’s heart rate might drop from 65 beats per minute to 12 or 15, it’s body temperature may only fall by 10 or 15 degrees to around 85 or 95 degrees Fahrenheit. While this provides a lot of water-cooler banter for biologists’ in their offices, it means something different to people like Joe Yarkovich, wildlife biologist for the Great Smoky Mountains National Park. Yarkovich has spent many winters following and monitoring bears in the Smokies, getting measurements and changing out telemetry collars and such, and he notes that one always has to be careful when approaching a “hibernating” bear.

The black bear’s warm body temperature during hibernation is also critical for the species survival because black bears give birth in their dens, in the winter. Most Southern black bears give birth from late December through February, and it’s their relatively high body temperature that allows the mother bear to be alert enough to care for her young. And that can be a demanding task. Newborns will nurse every 10 minutes or so. As they get older the intervals between feedings will grow giving the mom time to nap while the cubs nap.

Jumping mice join chipmunks and groundhogs and bats as hibernators in the Southern Appalachians while skunks, raccoons, possums, rabbits, squirrels (flying squirrels too,) river otter, mink, bobcats, coyotes, white-tailed deer and the newly released elk in Cataloochee Valley join those creatures that carry on through the winter months.

Just because they carry on doesn’t mean they don’t make allowances for winter. Dr. Muller points out that while white-tailed deer don’t hibernate their metabolism slows down and they don’t have to forage as actively as they do in warmer months. And Yarkovich notes that the newly released elk are, “…built for winter. They’re cold weather animals,” he said. “They molt twice a year and their winter coat consists of a woolly undercoat covered by thick guard hairs. I have seen them in the fields at Cataloochee many times with an inch or so of snow on their back that doesn’t seem to melt because they’re so insulated.”

Reptiles and amphibians are known as “ectotherms.” This means that they are cold-blooded—they have no way of internally regulating their body temperature. For most ectotherms, surviving the winter means finding a hibernaculum (den site) where the ambient temperature is above freezing. Most aquatic reptiles and amphibians seek out deep pools below the frost line. They can settle in to an ambient temperature that requires little in the way of energy to sustain their metabolism but keeps them above freezing. Sounds good, but how do they breathe? Well, Mom Nature is pretty resourceful—turtles have special tissues with minute blood vessels in their throat cavities and near their anus that allow them to extract oxygen from the water. Amphibians like frogs and salamanders can actually absorb oxygen through their skin.

Ward, an instructor specializing in “herps” or reptiles and amphibians, said that for most the goal is to avoid freezing because freezing creates ice crystals that rupture the cells and cause death. However, Ward said there are a few herps that ‘ain’t scarit.’ 

He noted that wood frogs, quite often, freeze at some point during winter. “They freeze solid,” he said. “Their heart stops beating and for all practical purposes they are dead.” But the wood frog is able to produce certain proteins (ice nucleators) and other anti-freezing agents that restrict the size of the ice crystals and determine where they might form so they do no harm to the cells. When ambient spring temperatures rise above freezing, wood frogs hoppily strike out seeking mates.

Did you know?

The monarch butterfly that returns to Mexico each fall is anywhere from four to six generations removed from the monarchs that first arrived in North America in the spring. 

Through the spring and summer the monarch’s life cycle is like most butterflies. As an adult, it reaches North America in the spring. It mates and dies. The caterpillars hatch, pupate, emerge as adults, and continue the northward trek. By autumn, some monarchs have made it as far north as Canada. 

The last emerging monarch of the summer doesn’t just mate and die. It is not sexually mature when it leaves the chrysalis. Instead, it turns south, and as an adult, routinely migrates as many as 2,000 miles, back to traditional wintering grounds in Mexico. Here it overwinters in colonies of hundreds of thousands. When spring arrives, this adult, now six to eight months old and sexually mature, begins the cyclic migration northward.

Migrating raptors in a thermal are called a kettle. Kettles can range in number from a half-dozen birds to thousands. Birds in a kettle rise or bubble up like boiling water in a kettle. When they reach the top of the thermal (sometimes three miles high) they set their wings and stream out, letting gravity take control. Raptors can often stream, or glide, for miles depending on the height of the thermal and weather conditions. It’s easy to see how kettling and streaming can be a very energy-efficient mode of travel for large raptors.

The scarcity of food is the primary impetus for migration and/or hibernation. It is not uncommon in the Deep South—Louisiana, Florida, Georgia—for male bears to be active all year if food is available. Females will still den, however, to give birth. 

Different species of snakes—like rat snakes, king snakes, rattlesnakes and copperheads—often den/hibernate together. Landon Ward, instructor of environmental studies at the University of North Carolina at Asheville, says there is no validity to the old tale that king snakes and/or rat snakes are “pilot” snakes, leading other snakes to good denning spots. “They end up denning together because it’s a good site—they’re all looking for the same thing; somewhere dry with a good ambient temperature.”

White-nose syndrome, named for the fungus Pseudogymnoascus destructans, has killed millions of hibernating bats across 25 states and five Canadian provinces since the winter of 2007-2008. The disease is known for the white fungus that infects the muzzle, ears and wings of hibernating bats.

All caves in the Great Smoky Mountains National Park and many others on private and public lands throughout the Southern Appalachians are closed or closely monitored to try and stop the spread of this deadly disease.