Waking up from winter: How dormancy and hibernation differ

Ever take a nap on a dark winter day and sleep so hard you don't know what hit you?

Or, are you the kind of person who can catch a few winks here and there, catnapping the winter away?

Either way, you have a lot in common with your wild kin.

Winter sleep is a universal strategy of getting through winter. Sleeping comes in many forms, and waking up is as important as the snoozing itself. Right now, as the days grow longer and the thaw-freeze cycle begins, wildlife is slowly emerging from its winter slumber.

Dormancy is a period of inactivity, either in winter or summer. Both plants and animals have dormant periods. If you're a gardener, you'll know that many seeds require dormant periods before they can germinate. Similarly, many animals need quiescence - a state of quietness or inactivity - and lots of organisms shut down during adverse conditions. Sleeping, it turns out, is a good avoidance technique when life's challenges are just too much to face.

Hibernation is a unique form of dormancy. If sold on the shelf, it would be Dormancy Extreme. It's triggered by day length and shifts in hormones, not just by a cold day here and there. When animals hibernate, their metabolism, respiration and heart rate drop drastically.

"While a normal body temperature (of a mammal) may be 95°F," according to the Illinois Department of Natural Resource's publication Wild Mammals of Illinois, "during hibernation it can drop as low as 36°F. A normal heart rate of over 100 beats per minute may drop to only four or five per minute. Breathing may slow to less than one breath per minute."

Hibernation is relatively long-term, but hibernators can and do wake up. In fact, the ability to wake up is important. A hibernating mammal, for example, may shiver a bit to warm up, fluff the pillows (rather, the grass and leaves), and fall back to sleep. Some might even get up to find their way to a deeper, warmer den.

Hibernation is not as common among mammals as many people assume. In our area, the only true hibernators are the groundhog (or woodchuck) and the thirteen-lined ground squirrel. The groundhog, of course, gets all the attention on Feb. 2. I'm for switching it up and calling next Feb. 2 "Thirteen-lined Ground Squirrel Day."

Torpor is the equivalent of Dormancy Light. Most of our native mammals experience torpor. It's brought on by immediate triggers, like temperature and food. (Compare this to hibernation's triggers, day length and hormones.)

Torpid animals slow down, snooze, and wait out the brutal winter storms, but they can get up and be active quite easily. They experience a drop in metabolism and heart rate, but not to the extent that hibernators do.

You might see a skunk or a raccoon checking out the garbage cans on a warm winter night, but see no signs of these critters when it gets cold again. It's as if these animals have roused themselves from a light nap, shuffled to the fridge, then moseyed back to bed.

Birds, reptiles and amphibians also retreat during winter. Only one species of bird is a true hibernator - the poorwill of western North America.

Hibernation, though, is common among reptiles and amphibians. A gathering spot for winter slumber parties is called a hibernaculum. Garter snakes are known for their hibernacula - rather, they're known for freaking people out when they emerge en masse in spring (not to worry, they're harmless - and beneficial).

Many frogs and toads burrow individually in hibernation. It's cause for celebration when one by one, the first brave chorus frogs croak their opening lines in the prelude to spring. Keep your ears open, because they may begin in just a few weeks, if the weather warms up.

The deep sleepers and the light nappers alike have just about depleted their winter reserves by late February. If you see a critter bumbling around on your back deck, bear in mind two important things: It's hungry, and it's "hormonal." In other words, the groggy wild animals you see now are focused on getting food and finding mates. They may be oblivious to you, or view you as a threat to their dating activities.

The days are getting longer, and wildlife is emerging. We all hit the snooze button and go back to sleep when it's cold and gray, but pretty soon the wildlife will be waking up for good.

Grab a cup of coffee, keep your eyes and ears open and wait for the miracle of spring to happen.

•Valerie Blaine is the Nature Programs Manager for the Forest Preserve District of Kane County. You may reach her at blainevalerie@kaneforest.com.