By Bob Engel
Marlboro College Professor Emeritus of Biology and Environmental Science
Is it safe to say humans regard snow in the same way that the other species do: as both friend and foe? In my case, being from a warm western state (42 years ago) I’ve never come to terms with snow. The fact that some people prefer the winter has always left me mystified.
The majority of the other species here are more strongly affected by snow than we are and with good reason—it can be the difference between life and death.
Let’s consider the potential benefits of snow first. Snow, especially fresh, dry snow, is full of air and is, therefore, a great insulator. Anybody down below—and this would include all herbaceous plants, lots of invertebrates, “hibernating” amphibians, and small mammals like shrews, voles, and mice—can benefit from that. All of a sudden, two feet of snow takes your thermal environment from the teens and twenties to the thirties and low forties. Who needs to go to Florida! A spring peeper under the leaf litter is much better protected from freezing solid with the snow.
That said, recent discoveries have indicated that some frogs tolerate partial freezing. What’s the big deal with freezing? Think of cells as soda bottles. When a cytoplasmic solution of mostly water freezes, it occupies about 10 percent more volume than it did as a liquid. So off goes the bottle cap and “pop” goes the cell!
Active small mammals, living in a now warmer microclimate—the subnivean space—are given an eating reprieve. Higher ambient temperatures mean less heat loss, which permits less food intake. Even black bears, who go to den about now, appreciate the layers of insulation. Bears do not really hibernate, dropping their body temps only a few degrees, but down there they stay until the end of March. So by all means, how about a blanket of snow?
There are occasional mysterious appearances by this small-stature crew. For instance, several times a winter I either see the short-tailed shrew itself, or its strange, twisting, insect-like trail above the snow. I can't fathom why it surfaces. The heat loss must be huge.
Overall, I imagine that these small mammals, who are food for almost everyone (foxes, fishers, weasels, coyotes and owls), feel pretty smug down there. Only weasels have any chance at getting them under the snow. But it’s got to be a deeper snow: one winter day, I watched a red fox work our field for meadow voles. There was maybe a half-foot of snow down, with some ice on top. The fox stopped periodically, twisted its head from side to side to listen to small sounds, and hearing what it wanted to hear, jumped up in a tight arch, broke through the ice and snow, and caught a vole 5 of 9 tries. With that success rate, I assumed I’d see it every day after that. Nope.
And here is the other side of the coin—what do large, active animals, especially the predators—do for food when the snow piles up? Owls in particular are in a bind with a lot of snow. That’s why they turn up at bird feeders. Their primary prey (small mammals) are often there to get discarded seed, exposing themselves to trouble as they do.
“Oh, but isn’t our biota adapted to all of this cold and snow?”
Yes it is, but only to a point.
Imagine three or four months of deep snow that increases the cost of travel, reduces food availability, and may include the metabolic costs of still more heat loss. Day after day, the winter grinds on. Your fat reserves slowly dwindle, then, with food harder to get, you start breaking down some of your other tissues. And then it snows again. The old go first, but even healthy stock may be pruned by a really snowy, cold winter. Some game animals like turkey and deer catch our attention first, but most populations might decline.
I used to teach a course called desert biology. Deserts can also be challenging environments; there are three options to consider when living there: escape, retreat, and tolerate.
As far as I’m concerned the same ideas apply here. The migrants (most birds and a few insects) have escaped. Our five true mammalian hibernators (including jumping mice and woodchucks), seeds and herbacious plant meristems, reptiles, and insect eggs and pupae have retreated. So have bears, and for periods of time, things like chipmunks. Everyone else tolerates winter. Some winters are more tolerable than others. After bad ones, it’s up to the tough survivors and a sometimes generous spring to replenish the world.