TIP: If you think the winter landscape is deserted, try looking for holes in the snow that lead to a secret city of tunnels where animals are active all season long.
Snooping along a snowy trail, I felt like I was the only creature alive. A glimmer of light sparked among the roots of a tree. On closer inspection, a little nook between the roots was framed by filigree of frost crystals. It seems I wasn’t alone after all, I just wasn’t looking in the right place! The hole, I suspect, was the entrance or air vent to the snow tunnel of a small animal, a doorway to the hidden life of winter under the snow.
So many animals stay active under the snow in winter there’s actually a word for that habitat: subnivean. (In Latin “nives” means snow and “sub” means under.) Beyond the crystal gates of this elegant-sounding kingdom are the dim halls of small mammals, fighting for survival.
Snow is a good insulator, the fluffier the better. About six inches or so will keep temperatures on the ground near 32 degrees, even when air temperatures dip far below freezing. Warmth from the ground melts away some of the snow next to the earth, leaving a space that small animals such as voles and shrews take advantage of for digging tunnels. Their activities draw predators such as ermine, owls, foxes, and coyotes. Even some birds are part-time residents of the world beneath the snow.
Ptarmigan, grouse, and snow buntings are all known to roost in the snow. A ptarmigan, for example, may fly directly into a fluffy snow bank, like pulling a blanket over its head. The bird will turn itself before settling in so that it faces a different direction. This is a smart escape strategy. If a predator finds the entrance, the bird can launch itself in a different direction than its pursuer expects.
Small mammals are full-time subnivean residents. Look for finger-sized holes that are ventilation shafts to let in oxygen, a precious commodity under the snow. You may have noticed hollows around dark-colored objects, such as rocks or tree roots. The dark objects absorb heat from the sun, melting some of the surrounding snow. These melted places may offer gateways to winter tunnels.
Voles, small mouse-like rodents, are one of the most numerous denizens of the shadowy subnivean world. They dig tunnels through the snow, munching their way through the subnivean supermarket: roots, mosses, lichen, fungi, grasses and seeds are available all winter under the snow. Sometimes voles dig up into higher layers of snow to access buried seeds higher up on plant stalks. You can look for tracks on the surface below branches where a vole made a brief surface foray, which will most likely lead you to a tunnel entrance.
Where a vole rests is focused on conserving heat. It may hollow out a sleeping area in the snow and line it with plants to make a cozy place to snooze. Some vole species, although they don’t congregate at other times of year, gather in “nesting” groups to conserve body heat. Sometimes they will drive off other voles that aren’t part of the group. Some voles may even start the breeding season in their frozen domain.
Shrews, voracious insect-eaters, also scurry beneath the snow. These tiny mammals are the furry equivalents of hummingbirds, with racing metabolisms that require refueling every few hours. They simply can’t slow down enough to hibernate. Luckily for them, many insects, from eggs to adults, overwinter under the snow. Shrews are merciless hunters; if they can’t find enough insects, they may hunt voles or even other shrews. Their tunnels can be extensive: one naturalist on the Yukon River tracked a shrew tunnel that was more than a mile long!
The hustle and bustle of shrews and voles draws the attention of predators. The long, low-slung body of ermine (the term for a short-tailed weasel in its winter-white coat) is perfect for zipping along tunnels after prey. Ermine require about half their body weight in food each day, so they hunt frequently. If they find good hunting grounds, they may cache extra victims in a “larder” chamber in their dens. Since ermine don’t pack much fat on their bodies, they may line their sleeping area with fur from their meals, a miniature version of a bearskin rug.
Larger animals that can’t slink into subnivean tunnels find other ways of hunting the small animals under the snow. Owls, especially Great grays, is one of the most dramatic predators. Using its acute hearing, the owl pinpoints voles or other scurrying tidbits up to a foot under the snow. Swooping low, it plunges into the snow with its talons, using its weight to sink down. If the owl judged correctly, it will fly off with a meal. The only traces the owl leaves behind for a wildlife spy to find are a hole in the snow surrounded by feather imprints from its wings at the scene of the crime.
Foxes and coyotes provide more comic relief than drama when hunting subnivean prey. They use their ears and sense of smell to search for morsels. The predator will perk its ears, maybe jerk its head side to side, then suddenly bounce into the air and land again on all fours. It may repeat this a few times if it misses. Not the elegance of an owl, but often effective.
In the last two decades, researchers have discovered something new and even smaller than shrews in the subnivean world. Microbes that form fungi and bacteria colonies become very active under the snow. Many of these species weren’t even known to exist two decades ago. These new microbes can be very specific in their nutrient needs and thrive in what used to be considered inhospitable conditions. It isn’t fully understood what they do, but they seem to have a role in storing nitrogen, drawing the nutrient from snow and decomposing plants. These microbes die when the snow melts away, releasing nitrogen that plants need for new growth in the spring.
Although they aren’t subnivean, ice worms deserve mention just because they’re so bizarre. These science-fiction-sounding relatives of the earthworm tunnel into ice on glaciers. It isn’t known how they accomplish this. Ice worms were discovered on Muir Glacier in Glacier Bay in 1887. Unfortunately for wildlife spies in Juneau, they haven’t been found on the Mendenhall Glacier or the Juneau Icefield.
Ice worms are segmented worms that grow to between a half-inch to an inch-and-a-half long. They feed on red algae that grows on top of the ice, and possibly pollen and other windblown matter. They survive best at around 32 degrees Fahrenheit. The worms can’t survive temperatures much warmer. At about 40 degrees Fahrenheit the enzymes in their bodies disassemble, making the membranes in the worm’s body fall apart so they appear to “melt.” The worms avoid this gooey end by staying out of direct sunlight, only coming to the surface of the glacier to feed at dusk or dawn or on cloudy days.
Next time you wander into snowy ground, keep a lookout for signs of life surrounding you.
• Beth Peluso is a freelance writer, illustrator, and avid birder. She enjoys spying on wildlife around Alaska.