Winter is rarely easy for anyone, but you may wonder sometimes just how wild animals make it through, lacking heat, cozy blankets, and hot chocolate or coffee to keep warm. As it turns out, they’ve evolved a fascinating array of physical or behavioral adaptations to either avoid or cope with winter’s woes. Naturalists sometimes simplify the approaches into three main categories: migrate, hibernate, and adapt, and there are all kinds of variations within each approach. Check out their special defenses against chilly weather and see what you can do to help them out a little.
Heading South—the “snowbird” solution…
Heading south for the winter—as many birds do to benefit from warmer temperatures and solve the problem of disappearing food sources—may seem like a simple solution. In fact, though, migration strategies are filled with potential hazards. Merely to make the journey requires amassing extra fat to use as fuel along the way. Small, migratory songbirds are at increased risk from predators and the vagaries of the weather while traveling and settling in unfamiliar places, while ducks and geese are subject to hunting along much of their migratory path. On balance, though, the gamble pays off, with enough birds safely returning in spring to start the next generation.
Hunkering down for the duration…
When temperatures plummet and daylight hours take a dive, heading below ground—or into some form of den—is the best solution for some animals. Bears may take shelter in depressions created under uprooted trees. Their metabolism slows to half its normal rate, enabling them to go without eating or being active for months. Woodchucks spend months fattening up so they can hibernate in their burrows for months at a time, too.
Beaver do not actually hibernate, but they remain in their lodges, benefiting from each other’s warmth—even with only two beaver in a lodge, the central chamber will stay well above freezing. By keeping activity to a minimum they can survive on limited amounts of vegetation, assembled in underwater caches or floating rafts. (In a clear sign that they know what they’re doing, they put branches of favored tree species on the lower portion of rafts, where they’ll remain accessible even after their pond ices over!) Chipmunks also do not hibernate. Instead, they come out to forage only on warmer days, surviving on the vast stores of food they gather in fall. Squirrels remain active, but create cozy microclimates within their nests by adding more material for insulation.
Frogs, toads, salamanders, and turtles take hibernation to an extraordinary level. They survive winter’s worst by entering a somewhat “frozen” state while remaining hidden and protected under leaf litter, moss, or decaying logs, or tucked within burrows or beneath mud on a pond bottom.
Hanging out in tough times…
Some animals don’t have the option of flying south, nor the ability to “chill out” for months on end. For them, coping with winter requires a combination of changes in their behavior, their feathers or fur, or their regulation of body temperature.
For mammals, behavioral adaptations can be as simple as curling up to reduce exposed surface area of one’s body, or bedding down under low branches in a cluster of pines for the reduced exposure they offer from the wind and the lingering effect of radiant heat they absorbed from the sun through the day. Birds seek shelter in dense vegetation or hollows within snow. When snow cover would make foraging nearly futile for deer, they conserve energy by simply resting on a sunny southward-facing hillside. In a more dramatic behavioral shift, some normally solitary animals, such as raccoons and porcupines, become “winter social,” huddling together in available den sites for the shared body warmth and reduced exposure of body surface area.
Many animals develop luxurious coats in winter, which often include soft, downy underfur. In addition, the hollow outer “guard hairs” of deer, foxes, and porcupines become much longer, increasing their ability to insulate. Birds’ feathers become more numerous and, in many species, change color to make the bird less visible in the winter landscape, protecting them from predators. And, of course, there is fluffing of both fur and feathers! By making the hairs or feathers more erect within their follicles, thousands of air pockets are created, greatly increasing their ability to provide warmth.
Regulating body temperature internally is another means to cope with cold. Some small birds, such as chickadees, decrease their body temperature a few degrees at night by having shorter, less frequent cycles of shivering. This lessens the heat flow from their bodies because it reduces the disparity between their body temperature and that of the air. Birds cannot compensate for cold by adding large amounts of fat because they must remain nimble enough to fly. Instead, they consume enough food each day to fuel their bodies’ energy needs to keep warm through the night. Regulating temperature can be selectively applied to specific body parts, too. Special vascular adaptations enable some animals’ appendages, such as the feet of geese and the tails of beaver, to be kept at lower temperatures than the rest of the body to reduce heat loss.
Some things you can do to help them cope…
- Add a clean, reliable source of water. Birds, especially, need water for bathing, which preserves the insulating ability of their feathers.
- When doing fall cleanup, create brush piles in the far corners of your yard, and leave some leaf litter behind for overwintering creatures and winter nest-lining material.
- Add native bushes and trees that provide natural sources of food in winter for wildlife.