Winter kills wildlife, or does it survive the cold?

Last winter many readers wrote to ask how wildlife could survive the frigid polar vortices. According to Pennsylvania Game Commission Press Secretary Travis Lau, the only documented wildlife casualties in Pennsylvania were about 165 mergansers and other waterfowl at Presque Isle Bay and Conneaut Lake in late winter. With most open water frozen, competition among waterfowl was intense.

Reproduction

PGC wildlife biologist Tom Hardisky’s worried that the cold winter might affect reproduction. “But we have not had a chance to measure that yet,” he said.

Paul Johansen, Assistant Chief of Game management, reports similar findings from West Virginia. “I’m not aware that last winter’s weather took a particularly hard toll on any wildlife, although we did receive some isolated reports of winter mortality in deer in selected counties,” he said. “I think most species did just fine, and we expect a good hunting season.”

Winter weather

Fortunately most wildlife species are well adapted to surviving extreme winter weather.

Fish slow down their metabolism and physical activity during winter, but they don’t mind how cold the air temperature gets. Because ice is less dense than liquid water, it floats so water never drops below freezing.

Sleep through winter

Reptiles and amphibians sleep through the winter season in dens beneath the frost line where their heart and respiration rates drop significantly. Aquatic species burrow into the muck to escape frigid air temperatures. And wood frogs can actually survive being frozen solid while hibernating beneath the leaf litter.

Most birds take the easy way out to escape winter weather. They migrate.

Brave the cold

Non-migratory species are well adapted to survive winter. They eat high calorie seeds, nuts, and animal fat to fuel their metabolic furnaces. They grow more down feathers to increase the body’s ability to insulate itself. And on the coldest days they hunker down to minimize their exposure to cold and wind.

Among mammals, ground hogs, bears, chipmunks, and jumping mice hibernate. Shrews and weasels stay active by using tunnels and trails in the subnivia, the microhabitat where snow cover meets the surface of the ground.

Muskrats and beavers build lodges with underwater entrances. Even when ponds freeze and are covered with snow, these rodents can slip freely into the water to feed on aquatic vegetation (muskrats) or the bark of limbs and branches (beavers) they’ve stored under the ice. Though muskrats are limited to wetlands or stream banks with sufficient water to cover their den entrances, beavers can manipulate their habitat by building dams to create ponds where food is available.

Gray, fox, and red squirrels fatten up in the fall and store caches of food they use throughout the winter. On days when the thermometer barely climbs above zero, they wisely stay in their dens.

Flying squirrels are much smaller than tree squirrels, so they lose body heat more rapidly than their larger kin. To reduce heat loss, they roost communally during the day. Sometimes a dozen or more flyers cuddle during daylight hours before venturing out at night to eat.

It turns out that cuddling is an effective technique for reducing heat loss and staying warm. Deer mice and bluebirds roost communally in hollow logs and old woodpecker cavities. Even tiny golden-crowned kinglets huddle through the night in the north woods, protected only by the branches of conifers.

Though most medium sized mammals such as raccoons, skunks, opossums, and foxes do not hibernate, like squirrels, they can hole up for days if need be. As long as these species enter the winter in good health, they can survive all but the most catastrophic winter conditions.

Severe winters can be problematic for white-tailed deer. Where deep snow is normal, deer often move to winter ranges where cover is better. These “deer yards” are typically in dense lowland conifer forests where there’s less snow, and winds and temperatures are moderated. Food quality in these areas is poorer so deer must rely more on stored fat. But that’s OK because even healthy deer normally lose about 25 percent of their body weight over winter.