Winter

White-tailed Deer In Snow

"I wonder if the snow loves the trees and fields, that it kisses them so gently? And then it covers them up snug, you know, with a white quilt; and perhaps it says ‘Go to sleep, darlings, till the summer comes again.'"

– Lewis Carroll, Through the Looking-Glass, and What Alice Found There


 

Winter is all about food availability and balancing energy expenditure with energy consumption.  PWLC animals survive winter in three possible ways.  Migrators travel great distances to find food in warmer climates and spend the winter actively searching out food, returning in the spring.  Hibernators stay here and sleep deeply through the winter living off of body fat built up from consuming extra food in summer and fall.  Resistors stay here and remain active, consuming food that is still available to them.   Let’s look at a few examples...

Migrators

There are two kinds of migratory birds:  those that leave here for the winter and those that arrive here for the winter.  Once our ponds, lakes, and rivers freeze over, waterfowl move on from the area and spend the winter in the southern U.S.  (A few hardy souls may stay behind in the city of Fergus Falls at the Waterfowl Sanctuary.)  Many duck, goose, and swan species join some of our songbirds there that already departed, like tree swallows, eastern phoebes, yellow-rumped warblers, house wrens, gray catbirds and brown thrashers.  Yet other songbird species continue on to Mexico and Central America, like wood thrushes and ruby-throated hummingbirds.  The longest distant travelers include our scarlet tanagers, eastern kingbirds, bobolinks, chimney swifts, purple martins, and certain shorebirds.  We must also remember the Caribbean destination for some indigo buntings and American redstarts, most black-throated blue warblers, and some palm warblers and prairie warblers.  (You can read more here.) Horned larks live here almost year-round, heading south only for the deepest, coldest winter months.  They are our last species to leave and the first to return as the distance travelled is so short. 

So winter bird life here is quieter but also graced with a few surprises landing from further north, like the occasional snowy owl, plenty of slate-colored juncos, American tree sparrows, and sometimes common redpolls.  Watch the roadsides and listen overhead for flocks of snow buntings, too.  For these species, the prairie of Minnesota is like Florida for us!

Hibernators

Chubby 13-lined ground squirrels hibernate in their burrows beneath the prairie.  They live off the fat built up through a busy summer of eating. Painted turtles head under water into the mud to hibernate (or “brumate” as it’s sometimes called for reptiles and amphibians).  Their metabolism slows so much that they get the little dissolved oxygen they need from the water through their skin.  However, you can possibly see them moving around ever so slowly under the ice. Frogs, on the other hand, still need a good oxygen supply and spend much of the winter lying on top of the mud or only partially beneath it. Some toads will dig deep burrows to get below the frost line in the prairie, taking advantage of pocket gopher mounds and tunnels.  Tiger salamanders also use gopher burrows but stay active below the frost line all winter long, as do gophers.  The land frogs, like the spring peeper, are particularly interesting. They crawl deep into crevices, where it gets well below freezing. However they don’t freeze to death. Even though ice crystals may form in the body or under the skin, high concentrations of glucose in the vital organs prevent them from freezing. These frozen frogs stop breathing, and their hearts stop beating. But when the weather warms, the frozen portions thaw, and the frog’s heart and lungs start again.

Resistors

Shrews, voles, and mice survive winter in the subnivean world, that narrow air space between the bottom of the snow pack and the top of the ground.  Converting plant material into protein, they form the basis of the prairie food pyramid, providing nutrition for other resistors, like weasels, mink, fox, coyote, northern shrikes, and great horned owls.  Muskrats and eastern cottontails, also resistors, help round out the carnivore menu.

Year-round resident birds must actively seek out food during winter days and build up enough fat to survive each nightly fast.  It is as if each winter day is one summer and they hibernate each night.  The tiny black-capped chickadee is a marvel at this survival pattern.  They reach an energy edge at 32 degrees F, and yet our winter nights get much colder than that and may be extended by blizzards.  Chickadees stretch their fat reserves overnight by lowering their body temperature and by shivering vigorously, maintaining a state of hypothermia.  In addition, they must also succeed in avoiding winy places and finding effective shelter at night with warmer air temperatures inside.  Their greatest heat loss is from the eyes and beak, so they sleep with their heads tucked beneath their shoulder feathers.  They fluff out their feather coat to trap warm air near their skin and ball up to sleep.  Chickadees have many other amazing adaptations which help them survive winter, like seed caching, an increased memory, and denser plumage.    Other winter bird residents include white-breasted nuthatches, pileated woodpeckers, American goldfinches, and American crows.

 

Yes, Minnesota winters are harsh, but wildlife is well-adapted, ensuring that the spring will be filled with new life once again.