• Ashley Reed

Hibernation or Torpor?

Nature Notes


By Ashley Reed

Emmet County Naturalist

Have you ever thought about what happens to animals during the brutal Iowa winters? The simple answer would be hibernation, however it’s much more complex than that! What if I told you only a select few animals in Iowa are true hibernators.

“Hibernation is a voluntary state an animal enters to conserve energy, when food is scarce, and minimize exposure to the winter elements. During hibernation an animal lowers its body temperature, slows its breathing rate, heart rate, and metabolic rate-the rate its body uses energy. Hibernation can last days, weeks, or months depending upon the species. Chipmunks reduce their heart rate from the usual 350 beats per minute to an almost undetectable 4 beats per minute during hibernation.” -Chris Bachman, National Forest Foundation

In Iowa, true hibernators include chipmunks, deer mice, and groundhogs as far as mammals go. Raccoons, opossums, skunks, and even bears enter a lighter state of sleep called ‘torpor’. While in torpor, these animals still enter a deeper sleep but the difference is they are able to wake up. That is why it is not uncommon to see these animals out and about during the nicer days of winter. Especially after the harsh cold of January, I would expect to see animals out trying to find food while it is warmer. Small mammals are going to hibernate because it is much harder for them to keep up with their high metabolism.

Now that we’ve talked about mammals in the winter- what about the other animals. Many birds migrate south when the colder months come around but others stick around. There is a good amount of backyard birds that stick around during winter, along with our birds of prey. When you look at birds this time of year, you may notice they are puffed up. Bird feathers are designed to create wonderful insulation for the bird. They puff up their feathers to trap warm air. Some birds such as the Snowy owl even have feathers on its feet for added insulation.

Fish enter a light torpor and hang out on the bottom of the lake or river. During the winter- the bottom of the lake is the warmest place to be. The warm water sinks in the winter and in the spring the lake will turn over, meaning the warm water will rise as the temperatures rise.

Now this is where it gets interesting. Many insects will die off in the fall and their eggs that they laid is what hatches in the springtime. Some insects such as native bees hibernate underground. Amphibians also hibernate underground. Insects and amphibian bodies produce a substance that is very similar to antifreeze! This allows them to essentially become an ice cube during the winter but the antifreeze in their blood and circulatory system keep their vital organs safe. Now if that doesn’t impress you then I don’t know what will.

Iowa reptiles also enter hibernation. Aquatic turtles will hibernate in the water and they are able to switch their bodies to breathe underwater and go the whole winter without coming to the surface for air! Snakes such as garter snakes are a communal species and like to find an abandoned badger hole and pile in for the winter. During the spring time you can spot hundreds of snakes coming out of their hibernation hole. Probably sounds like a nightmare to some, but a dream to me!

Animals have adapted to live in the harshest of weather and it is simply amazing. Even the ‘simplest’ of animals have evolved to overcome and survive and I think that is fascinating. I however, have not adapted and can not wait for warmer weather.


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