Winter 1998

[TEXT ARCHIVE WEB-PUBLISHED AUGUST 2001.
ORIGINAL PRINT PUBLICATION DATE: WINTER 1998.]

Animals in Winter
By Jerry Sullivan

Life often hides in winter. But it's there. Everything seems still and motionless until you hear the black-capped chickadees.

Turn toward the sound — chick-a-dee-dee-dee — and you can see the tiny birds tumbling through the branches. Often hanging upside down from tips of twigs, they flit from the crowns of trees to the lowest limbs. Sometimes, they leave the trees to cling to the stems of wild bergamot or woodland sunflower to feed on any seeds remaining in the dry brown flower heads.

They are usually not alone. White-breasted nuthatches and sometimes red-breasted nuthatches work the tree trunks and larger limbs, hunting head-downward on the trunks. A downy woodpecker may be hitching its way up the trunk, looking perhaps for the eggs, larvae, or adults of cucujid bark beetles. These flattened insects are ideally constructed for slipping through cracks under dead bark. They sleep through the winter protected by glycols, natural anti-freezes that prevent their bodily fluids from freezing even in frigid weather.

Sometimes brown creepers, tiny brown birds that work the tree trunks like woodpeckers, are part of the flock. Golden-crowned kinglets, the second smallest — after hummingbirds — of North American birds, may join in too.

Mixed flocks like these are a common feature of bird life. In the tropics, mixed flocks are present year around. Here in the mid-latitudes, they are a strategy for coping with winter, the lean season, the harsh time that every living thing must learn to survive.

Most of the plants of the Chicago Wilderness cope with winter by going into a dormant phase. The trees and shrubs lose their leaves. Long-lived herbaceous plants survive the winter by dying back to their roots and staying underground until spring. Annual plants spend the winter as seeds.

For animals, there are several possible strategies, each with a number of variations. One strategy is to leave, to seek out places where the air stays warm and snow and ice don't cover ground and water. Monarch butterflies do this as do many birds that nest in this region.

Another strategy is to sleep through the hard times. Frogs, snakes, turtles, insects, and some mammals use this method. Among mammals, the intensity of the sleep varies. Woodchucks go into the deep sleep of true hibernation. In the relative safety of their burrows, their body temperatures drop to around 40° F and their metabolisms operate so slowly that they can survive on the fat they accumulated the previous summer. Gray and fox squirrels and raccoons, among others, are active throughout the winter, but may sleep through the coldest days and the deepest snows.

Some animals — deer mice and meadow voles among them — store food for the winter in caches which they visit periodically. Gray squirrels bury acorns and other nuts in individual holes. The nuts they fail to collect play a major role in sustaining forests.

The final strategy, that of black-capped chickadees, white-tailed deer, least weasels, cottontails, and coyotes, is just to tough it out. These creatures scratch out a living in the face of subzero temperatures, deep snows, and howling winds. Maintaining a constant body temperature in a Chicago January takes a lot of calories.

All these animals are living on a legacy. They are feeding off the production of last summer. With nearly all the plants of their environment closed down for the winter, the herbivores are eating the seeds, fruits, buds, twigs, and bark produced during the past growing season. The carnivores are eating animals kept alive by those seeds, fruits, buds, twigs, and bark. The bitter cold of January is a bad time, but March can be even harsher. By then, the animals of winter are foraging through a landscape that has been relentlessly picked over for months. The leanest times may be just before the new spring growth begins.

The mixed flocks of birds that bring life to the winter woods are carrying out an effective strategy for dealing with winter. At the heart of each flock are black-capped chickadees and tufted titmice with other species gathered around them.

Chickadees are very alert for predators, and observation has shown that birds of other species respond to the alarm calls of chickadees, either freezing where they are or diving into cover and then freezing.

The dominant male chickadee sounds the all-clear when the red-tailed hawk or kestrel has passed by, and all the birds of the flock resume their feeding.

Close observation has shown that birds in a flock spend more time feeding and less time scanning the skies for danger than lone birds. One study found that downy woodpeckers feeding on tree trunks stop from time to time to scan the skies in a characteristic head-cocking movement, alternately looking left and right to locate predators. Lone birds averaged 20 head cocks a minute. Birds with one or two companions averaged 13 head cocks per minute, and birds in flocks of three or more averaged only six head cocks per minute.

It is easy to understand what the other species get from flocking with chickadees. But what do the chickadees get? The answer seems to be cannon fodder. Observe a passing mixed flock and you are likely to see the chickadees in the center with the other species scattered around the perimeter — just where they would be most vulnerable to a passing hawk.

Many animals depend on old woodpecker holes drilled into the wood of standing dead trees. Chickadees may nest in them in summer. In winter, a whole flock may pack itself into a single hole, combining the body heat of several individuals into one warm, feathery mass. Standing dead trees — foresters call them snags — play a major role in forest ecology serving as sources of both food and shelter to everything from beetles to flying squirrels.

Most mammals are elusive critters, generally much harder to observe than birds. You may see deer, squirrels, or cottontails anytime you take a walk in a nearby natural area. But you can go for years without laying eyes on a weasel, deer mouse, or red fox.

The best time to learn about the lives of these animals is winter, when snow turns the ground into a visual record of recent events. Pick up a guide to tracking — such as A Field Guide to Animal Tracks by Olaus J. Murie in the Peterson Field Guide Series. Murie discusses the habits of these animals of winter and provides illustrations not only of footprints, but of twigs nibbled by cottontails, trees girdled by beavers, and the nests built by squirrels among the bare branches of winter trees.

At the edges of woodlands and out on the prairies and grasslands of Chicago Wilderness, small birds could run afoul of the tiniest carnivore in North America, a ferocious little killer called the least weasel. Of course, if you have to make a living by hunting and you weigh only two ounces, you had better be ferocious and opportunistic as well. It also helps to be elusive and, if my investigations are any indication, least weasels have carried the business of elusiveness about as far as it can be taken.

Chris Anchor, wildlife biologist with the Forest Preserve District of Cook County, occasionally gets reports of least weasels falling into a window well or otherwise trapping themselves, but no local guidebooks list "window wells" as good least weasel habitat. Dan Ludwig of the DuPage County Forest Preserves has seven records for the species since 1980 in preserves in the western part of the county, but most of the records are of ex-least weasels, the bones of animals dispatched by great horned owls and then regurgitated in owl pellets. Great horned owls can teach even weasels a lesson in ferocity.

Wild animals usually live without cushions. They are almost always just one step ahead of destruction, but the struggle of the least weasel seems more desperate than most. The villain here is a simple fact of geometry: the smaller you are, the greater the ratio of surface area to volume. A least weasel is mostly surface, and every square millimeter of that surface is constantly radiating heat. Calories are just pouring out of these animals, and hunger means not an unpleasant feeling in the pit of the stomach, but eventually death.

Your chances of seeing a least weasel are exceedingly slim, but tracks in fresh snow might let you know that one has passed by recently. The animals usually move in leaps. Often the tracks of the rear feet are directly over the tracks of the front feet. The feet are oval, and a good print would show the impression of the five toe pads. However, all five are rarely visible.

If you come across a weasel's track, follow it. It will give you a look at a highly active, inquisitive predator on the hunt. Leaps will vary from a few inches to few feet. You will probably see many changes of direction and lots of attention paid to the undersides of fallen logs. Sometimes, weasels dive into deep snow as if it was water. You will see a hole in the snow in one spot then no more tracks until another hole in the snow several feet farther on reveals where the animal emerged.

Think weasel tracks and you will start noticing raccoon and mouse tracks as well as the remains of a hickory nut eaten by a squirrel. You will notice the cottontails crouched in the brush, and you might even find an owl pellet with its history of the bird's most recent meals.

Least weasels are looking mainly for mice and voles and so are owls and foxes and coyotes and every other meat eater in the world. Mice symbolize timidity, but to me it's a bum rap. Imagine the courage it takes to try to live your life in a world where everything eats you. We have several different species of these courageous little rodents in Chicago Wilderness. In prairies and grasslands, deer mice and prairie voles can be found. If the land is wet enough, meadow voles appear. These prairie species are burrowers, a useful trait for small animals living in a fire-dependent community. Voles create runways for themselves, tiny tracks under the shelter of grasses and other plants that provide hidden routes for travel between burrow and food. In winter, these runways are safely under the snow where they provide extra protection from predators.

In woodlands, look for the tiny tracks of white-footed mice in the snow. Their hind feet show five toes; their front feet four. They sometimes leave tail tracks as well as foot marks. They often take over last summer's bird nests to shelter them through the winter. If you came across an old robin's nest that has been roofed over, you would be looking at a white-footed mouse nest.

You may never see a coyote. And it could take you years to learn to distinguish coyote tracks from the footprints of somebody's family dog. But if you come across something that looks like dog droppings except that it is black and contains a considerable quantity of hair, you can recognize it as coyote scat. It will be easy to find. Feces are a form of communication for coyotes; they like to leave them right in the middle of trails.

In the stillness of winter, the signs of life stand out. Keep your eyes open for a red-tailed hawk hovering over a grassy meadow. Listen for the yanking call of a nuthatch. Watch for the flattened grass on last night's deer bed. Follow the tracks of a white-footed mouse from nest to larder. The stories are there and you can learn to interpret them.

Jerry Sullivan is a naturalist on the staff of the Forest Preserve District of Cook County.