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Winter sleep

January 28, 2018
Kevin Williams - Grundy County Conservation Director , Reinbeck Courier

Well, the extremely cold temperatures have subsided for a time this winter. It feels like March as I am writing this but I'm sure I should not dig out the short-sleeved shirts and jackets to replace the sweatshirts and winter coats. The Carharts hanging in the back hall will be called into action again. We humans have to be prepared for anything and everything when we are going to spend the winter in Iowa. But a few of our other mammalian friends have other options. I am talking about winter sleep.

Many of the mammals that reside year around in Iowa utilize some degree of "winter sleep." For the purposes of this column, I am calling everything from a few days of inactivity all the way to hibernation as winter sleep.

A host of Iowa mammals utilize the "few days of inactivity" kind of winter sleep including skunks, raccoons, and opossums to name just a few. During a winter storm, for instance, these will curl up in their den and conserve energy by spending 24 to 36 hours doing little else than sleeping. But if you were to crawl into the den and bother them, you would find out very quickly that they still have sharp teeth and claws and could use them. And following this relatively short quiet time, they need to break out of the "house" to rehydrate and seek nourishment. I have a vivid memory of one winter on the farm where following a winter snowstorm I was walking the fence line looking for a pheasant. The dog stopped, cocked his head, and suddenly started digging straight down into a snowdrift. To my surprise, there was some growling and he was into a fight with a raccoon that hadn't decided to come out of that winter sleep yet.

Then there are the mammals that are "weak" or restless hibernators. These are relatively inactive from late fall through the winter months. Eastern Chipmunks for example "wake up with the munchies" several times during the winter and take advantage of the cache of food that they stored underground in their burrow only to return to that hibernative state.

True or "deep" hibernators by comparison pretty much enter hibernation and stay that way until spring. Woodchucks (you might call them groundhogs) and thirteen-lined ground squirrels (you might know them as grinnies or squinnies) are examples of true hibernators here in Iowa.

When I was going to school at Iowa State, I had a lab where we studied hibernation. It might have been physiology or it might have been mammalogy. Which course it was might escape me but the lab experiment was particularly memorable. It involved inducing the hibernation response in thirteen-lined ground squirrels by literally placing them in the refrigerator! The next day we removed the sleeping little animals and carefully attached them to monitors that recorded their respiration, body temperature and heart rate as they slowly warmed and came out of hibernation.

My strongest memory of the lab was that you could literally roll them like bowling balls down the lab tables. I'm sure that college students would never do that today.



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