February 18, 2015

The Wonders of Winter Survival

A couple of days ago I was amazed and elated watching this little creature––a wooly bear caterpillar––move in my hand; it waved its little legs and raised its head. Oh wow! OMG!! It's alive!

Why was I so thrilled? because a couple of days before I'd brought it inside from the shed, where it was curled up frozen solid from winter's cold. For me this was a little experiment, a test to see if it really was true that some animals survive winter by freezing. I just read a wonderful book about animals in winter––Winter World: the ingenuity of animal survival by Bernd Heinrich––which described the various strategies of getting through winter, from using anti-freeze, to powering down into torpor, to huddling together, to shivering, to lowering body temperature. Any one of those things is amazing. We homo sapiens survived moving north by using fire, wearing clothing, finding shelter; for animals other than us, only shelter is a survival mechanism used by some.

Regarding insects Heinrich writes:
Insects exhibit an exhilaration and a celebration of the exceptions, where anything goes that can.
Each insect species has a life stage at which it gets through the winter. For the Isabella Tiger moth, it is its larval stage, the wooly bear caterpillar. For the beloved Charlotte the spider––the barn spider––it is its eggs; you can see a dead spider at the bottom right, egg masses at the top of the photo above. The insects use a substance in their tissues––glycerol and sorbitol, which are alcohols, converted from glycogen––that act as antifreeze.

A couple of well-loved frog species in my area––wood frogs and peepers––survive winter by freezing solid, just like the wooly bear. It's hard to believe that this plump and active leaper becomes a block of ice in winter. Toads dig themselves into unfrozen ground and hibernate, keeping their body temperature a little above freezing, but the wood frog, gray tree frog, chorus frog, and my favorite spring peeper, all can be frozen in winter with no ill effects. Similarly to insects, they use alcohols to allow ice to form between the cells, but not inside them, which would be deadly. Heinrich describes the miraculous:
In about fifteen hours, the frog is frozen solid except for the insides of its cells. Its heart stops. No more blood flows. It no longer breathes. By most definitions it is dead. But it is prepared to again revive at a later date. 

I saw this black bear in the field in front of my house last spring. During the summer into fall, it likely ate ravenously, storing up lots of fat for its winter hibernation. When the weather began to get cold, it found a nice den in which to spend the cold months. There are interesting things about bears in hibernation: their body temperature does not go down more than a couple of degrees but they don't drink or urinate all winter; although they are sedentary for months, they don't lose bone mass. How, Heinrich asks, are they able, after five months of rest, "to get up and walk up a mountain"? No bed sores, no major loss of muscle mass, no hardened arteries from all the fat they consume.
We inadvertently simulate a hibernation-like state of inactivity in our modern environment, a new state of nature to which we are not well adapted.

Golden-crowned kinglet
Photo by Gary Irwin, courtesy of Wikipedia

One of Heinrich's favorite mysteries is how a tiny bird––the Golden-crowned kinglet––with so little body mass to keep it warm, can survive northern winters. It is smaller than a warbler, not much larger than a hummingbird. They have to eat constantly in order to have enough weight to make it through the losses of the cold nights. They do things that other birds do: fluff up their feathers to create air pockets and thus more insulating warmth, huddle together in a shelter, shiver to warm the body. In the end, Heinrich believes it's a matter of luck for individual survival, with a good balance of various strategies. I love what Heinrich has written about these birds, ending his fascinating book:
Undampened enthusiasm and raw drive would matter. I do not and cannot ever know the combination of happiness, hunger, or emotions that energize a bird. But whenever I've watched kinglets in their nonstop hopping, hovering, and searching, seen their intimate expressions, and heard their constant chatter of tsees, songs and various calls, I've felt an infectious hyperenthusiasm flow from them, and sensed a grand, boundless zest for life. They could not survive without that in their harsh world. Like us, they are programmed for optimism.
....They defy the odds and the laws of physics, and prove that the fabulous is possible. 

*I'll be away for a few days; see you next week. 


  1. I have read several of his books, this one included. Wonderful reading. I hope you have a grand time. Someplace warm anyway so you can thaw out for awhile.

    1. Heinrich is a terrific writer. I've read only one other of his books––The Geese of Beaver Bog––which I loved, but I will read more. Ravens in Winter is probably next.
      No, no place warm; just NYC and a visit with family and to see friends and art.

  2. Oh DO read Ravens in Winter... I read Winter World a while back and was fascinated, especially living in the forested hills of Massachussetts and getting to learn about all the creatures I live with. Living with a large population of ravens, I learned so much about them from Ravens in Winter.

  3. Nice.
    Reminds me of my favorite winter companion around here - the Carolina wren.
    Bring us some good stuff from NYC.

  4. thanks for reading and commenting, Valerianna, Ravenna, and JBS.

  5. This looks like a fascinating book.
    Here in the UK, we have recently been enjoying a lovely series on the BBC on Alaskan wild life. Among much else, there was extraordinary footage of a species of a hibernating arctic ground squirrel that lives in Alaska and whose body temperature drops to - 3C for several months of the year. Extraordinary resilience!