This has been a difficult weather week for many people across the eastern half of North America. Strong winter storms have dropped tremendous amounts of ice and snow, and extremely cold temperatures and strong winds have made it difficult and unsafe for people to be out and around. We were on the western edge of this storm here at home, so just had strong winds and a little snow (though still enough to cancel school for two days). While I was sitting inside my warm insulated house, watching the wind blow the snow around town, it was hard not to think about all the creatures who have survived weather like this for thousands of years – without any of the comforts we see as basic necessities.
Species that don’t migrate to warmer climates have a couple of choices for survival when temperatures drop. First, they can either hibernate or enter some other form of dormancy for the majority of the winter. Second, they can stay active and survive as best they can – usually losing much of the fat reserves they build up in the fall. Third, they can hide away during bad weather and search for food when temperatures are more moderate. Late last year, I wrote an article for NEBRASKAland magazine summarizing some of the specific winter survival strategies used by Nebraska animals. If you’re interested in learning more, you can read the full article here. Otherwise, here are a few short anectdotes you might find interesting…
Insects overwinter in a variety of life stages, including eggs, larvae, and adults. Most enter some level of diapause (a rough equivalent of hibernation for insects) in order to survive. Those insects that overwinter as adults typically try to find some shelter by burrowing underground or at least into leaf litter or other insulating matter. Even there, many of them end up freezing solid, only to thaw out and resume life in the spring. I found this water boatman near the frozen surface of a shallow prairie wetland. According to several sources I’ve found, these and many other aquatic insects can remain at least somewhat active in the water beneath the ice for much of the winter, but if frozen, can simply thaw out and start swimming around again in the spring.
Leopard frogs, according to the research I did for the magazine article, are supposed to hibernate on the bottom of ponds where the temperature stays above freezing. They settle into the sediment at the bottom of a pond, but leave space around the sides of their body where their skin can extract oxygen from the water in sufficient quantities to survive the long winter. Imagine my surprise, then, when I saw this leopard frog SWIMMING across the bottom of a shallow creek the other day in sub-freezing conditions. Now, it wasn’t swimming very fast, but it was certainly swimming – not just drifting with the current. I imagine the groundwater-fed stream was warm enough that it provided the same above-freezing temperatures frogs get from pond bottoms. In fact, a stream probably has higher oxygen levels. But still – there was ice along the edges of the stream, and when I saw it stop swimming, I was able to catch up with it and photograph it sitting underneath some of that ice. It’s not a great image from a photographic standpoint, but tells a story. I’m not really sure why it was swimming when I saw it (Was it disturbed by me walking by? Did it get hit by something floating downstream? Does it have to move periodically to avoid getting buried by sediment?) but it gave me something intriguing to wonder about on a cold winter walk.
The opossum is one of a large number of animals (especially mammals and birds) that fit into the “hybrid” strategy category. During very cold stretches of weather, it stays hidden away in a burrow and has a lower-than-normal heart and breathing rate to conserve energy. When temperatures warm to a certain point, however, it ventures out to forage and recharge its stores of energy. This one was poking around in the snow by some tree piles we’d burned the day before, apparently looking for food – but probably also enjoying the little bit of heat still emanating from the remaining embers. Judging from its uninsulated pink toes and nose, it sure doesn’t look like much of a snow creature (and they do often have ragged frostbitten ears by the end of a hard winter) but oppossums have been around long enough that it’s hard to argue with their success.
Ok, so a chickadee is not exactly a prairie species, but it is a good example of an animal that is known to use a strategy called “daily torpor”. Chickadees can drop their body temperature a few degrees overnight to save precious calories from being burned during a period when they’re not planning to move around anyway. Many other birds and small mammals are thought to employ the same strategy, but there’s not much data (that I could find) on the topic at this point. It certainly makes a good deal of sense, although you’d want to be sure you were in a nice secure place before you dropped into any kind of torpor while owls and foxes were patrolling nearby.
Regardless of your personal strategy for getting through the winter, I hope you’re enjoying this one so far. Groundhog day has passed, so depending upon your local “hognosticator” you may or may not have a lot more winter to look forward to.
I think I’ll enjoy myself a little daily torpor.