The Science of Surviving Winter

Heated gloves, snow tires, cold-weather clothes and groceries purchased in bulk or delivered to your door… come December, our lives are supplemented with gadgets and remedies so that even in the biting cold of deep winter, life can continue uninterrupted by weather. We shift our priorities and the timing of our routines, just like our wild counterparts also enveloped by winter’s cycle. 

But for other animals, there is no retreat to cozy fireplaces and piping hot soup. How do wildlife cope so well with the shift of seasons? Physiological and behavioral adaptations are the secret to their success — here are just a few of the strategies that help Iowa wildlife survive the winter. 

Leave the state (or country)

Most Iowans are familiar with the seasonal departure of birds and monarchs who, depending on the species and where they started, might travel to the next state south or as far as South America. The American Redstart, a petite and chatty warbler that raises young in Iowa summers, ventures as far south as Belize and Guatemala to find adequate food and warmth. Monarchs, an insect the weight of a paperclip, leave Iowa in early fall with a very specific final destination — the oyamel fir forests in central Mexico. All monarchs east of the Rockies aim for this patch of habitat, which is around 6 hectares (about 15 acres).  

Not all bats seek shelter in your attic. Around half of Iowa’s bat species migrate to warmer climates or the sanctuary of caves and mines in eastern Iowa or Missouri where they’ll hibernate. A handful of Iowa’s dragonfly species also flee the state including one of our most plentiful, the common green darner, which can travel as many as 80 miles per day on their journey to Central America. 

Laying low

There are a few strategies related to reduced activity, and a variety of overlapping terms to describe it. Depending on the species and timing, it might be called:

Hibernation: a prolonged state of sleep or inactivity, usually used to describe mammals

Brumation: a state of dormancy, usually used to describe cold-blooded animals

Torpor: short-term inactivity, lasting a few hours to several days

Diapause: a state of suspended development, usually used to describe insects or other invertebrates

For example, the limiting factor for fish is not temperature, but available oxygen. Most fish species move to deeper waters where there is more dissolved oxygen, and are generally lethargic, sluggish and consume less food. Some species will rarely feed if the water temps drop below 40 degrees. 

Leopard frogs and turtles also spend winter on the bottom of water bodies, absorbing oxygen through their skin or cloaca.

American toads escape winter’s grasp by burrowing underground below frost level. 

In Iowa, a variety of insects, such as bees, mosquitoes or cockroaches, overwinter by entering a state of suspended development and reduced metabolic activity (diapause). While most butterflies and moths spend winter in their chrysalises or cocoons, the regal fritillary and Isabella tiger moth (the adult form of wooly bear caterpillars) both overwinter as caterpillars. A few butterflies, like the mourning cloak, can spend the winter as an adult, tucked away in fallen leaves and other plant matter. 

And every fall, all bumble bees die except the fertilized queen from each colony, who overwinters in vegetation. She emerges in early spring to solely create the next generation.  

Cool party tricks

Other niche adaptations help our wildlife brave the cold.  

Waterfowl stay warm in chilly waters with a special blood vessel adaptation that allows them to use counter current heat exchange — moving heat from warm arterial blood to veins carrying cold blood. 

Insects in winter diapause create antifreeze-like compounds that protect against ice formation within the body. But some insects employ the antifreeze strategy without slowing down. Snow fleas, harmless tiny springtail insects, continue moving all winter long, believed to be feeding on fungal spores and algae on the surface of the snow. 

Some animals simply hide in plain sight. All short-tailed, and some long-tailed and least weasels (especially those in northern Iowa), change their coloring to blend in and avoid predators. They shed their brown summer coat around the time that snow starts flying in exchange for crisp, pure white. This new outfit makes it difficult for eyes to pick them out against a snowy backdrop. 

Have you ever seen a particular puffy bird in winter? They didn’t pack on the pounds — they create their own insulation by fluffing up, trapping air in the negative space between their feathers to keep the cold farther away from their bodies. 

While Iowa doesn’t have many, bison are especially adapted to harsh winter conditions. They grow thicker coats, gain weight, and move snow with their strong necks and huge heads to find grasses. It’s estimated that bison can withstand temperatures as low as -40 degrees Fahrenheit. 

The next time you bundle up to shovel the driveway or quickly check the mailbox, take a moment to acknowledge our hardy and incredibly diverse wild companions, each navigating winter in their own way.