I’m still suffering from a cold and/or a sinus infection that I’ve had since the first of the year, and still suffering from laryngitis (which means I haven’t really “spoken” since “last year”). I’m basically hating 2010 so far.
But at least I’m here in my house, which is a pleasure palace of warmth compared to what the world outside is experiencing. Drafty windows? Is it a little chilly in here? Who am I kidding. Look at those birds out there.
The birdfeeder is insanely popular today, and for good reason: Those birds and squirrels are stoking their metabolic rates so that, with the magic of insulation, they can shiver all night long and survive until morning.
That cardinal has no more mass as that can of beer on the sunporch that we had to bring inside, lest it freeze and blow up. Why doesn’t the little birdie turn into a block of ice, like the brewski would?
Humans are in the same boat, only we are smart enough to have figured out how to burn something outside our bodies to keep from freezing solid.
Critters and plants don’t have that option, however. So they have to do other things to survive:
1. Move to warmer climes; migrate.
2. Go dormant or hibernate.
3. Just keep a-goin’; thermoregulate.
4. Don’t survive; die and leave behind dormant offspring so they can carry on life whenever it warms up.
1.
We have examples of each category right in our backyard. In the first category, we most obviously have bird species who have gone bye-bye for the winter, returning to their homes in the tropics or even just the southern U.S., since they only came here to breed, anyway: Orioles, wrens, hummingbirds, catbirds, warblers, tanagers . . . And monarch butterflies migrate south, too.
I think we can also count all our tropical houseplants in this category, as they spend their summers enjoying the sunshine and rain in our backyard, but each winter migrate (with a good deal of assistance from us!) into the warmer climate of our household.
2.
Then there are the hibernators, whose bodies decline to fight hard against the cold. Instead of trying to stay warm and active during the winter, these organisms enter dormancy of various kinds. Our woodchucks grow slothful as the temperatures drop in early winter; they’ve spent the summer building up fat. They eventually creep into their burrows one day to go to sleep and not reawaken until the warmth of spring.
During hibernation, a mammal’s body temperature falls in response to cold, and metabolic processes drop with it. Oxygen consumption plummets, heart rate is greatly reduced, and there can be long periods of suspended respiration. But when temperatures drop below freezing, almost all hibernating mammals have to thermoregulate somehow (that "warm-bloodedness" kicking into gear), or else they would become a block of ice. Thus the fat layer they've built up that can be burned; thus the importance of good insulation from fur, fat, soil, and even snow. All of this is because there’s not enough food available in winter to supply the tons of calories these critters would need to keep warm and normally active. In winter, they simply check out of the system.
Reptiles and amphibians enter dormancy, too, of a different kind. They don't thermoregulate internally like mammals and birds do. Most of them, from toads to box turtles to garter snakes, instinctively burrow someplace low as the temperatures grow colder in the fall. I’m pretty sure I know where the garter snakes like to overwinter on our property; one hole is on our front terrace by the ash tree, another’s in our backyard, where some remains of an old house still moulder beneath ground level. I’m sure there are crannies among that buried rubble where the snakes take shelter, in a group. I think they also have hidey-holes against our stone foundation, especially in the front, which faces south.
Box turtles seem more haphazard about their burrows; as winter closes in, they push headfirst into leaf litter, swimming persistently with their forelegs into the earth; if they’re lucky, they do this in a place where the soil is soft enough to be workable, and the turtle can get a decent amount of cover up over its shell before all this horrible cold sets in.
Although recent studies have shown that box turtles (and some frogs, and numerous other creatures) can have a kind of “antifreeze” in their blood to prevent them from freezing solid and sustaining tissue damage, no doubt many box turtles do lose their lives on these bitter cold nights, dying as they sleep, to become food for the soil, the earthworms, and the hungry scavenger-carnivores once their bodies start to thaw.
But the most obvious dormancies are all around us: The trees, which stand quietly, accepting everything that befalls them; their defense is to drain liquids belowground, below frostline if possible, and then to be flexible enough to bend under the weight of snow and ice, or strong enough to withstand it. Deciduous trees drop their leaves before the snows start, reducing the amount of snow that might collect otherwise. Years where the snow comes freakishly early, before leaf fall, can wreak havoc with broken limbs. Conifers, evergreens, tend to grab lots of snow—but they make up for it in their ability to bend without snapping under the weight.
Some trees, such as ashes, have branches configured in softened Vs that make it easier for precipitation to drip or slide from them toward the strong trunk and onto the ground, reducing the amount of weight to be borne by the branches in the first place.
Less obvious vegetative dormancies occur underground: the daffodils, the tulips, the dandelions and parsley, irises, dame’s rocket, peonies, grasses of all kinds, coneflowers, mayapples, and the myriad of other herbaceous perennials that die clear down to the ground, leaving only dry, withered husks to sink beneath the accumulating snow. Perhaps because these plants disappear so thoroughly from view during the winter, their reappearance in spring can thrill us beyond words.
3.
Into the third category fall ourselves and all the birds that visit our feeders: Those that thermoregulate and stay completely active, burning food, burning fat, or (like us) burning wood, coal, and natural gas to stay warm. We are textbook cases of endotherms; unlike snakes that must warm themselves by sitting in the sun on a warm rock, we maintain our preferred body temperature with our own metabolisms.
Endotherms are like little cottages with a woodstove inside to generate heat, and good insulation to keep the heat in. It takes a lot of wood to make it through a cold winter, but it’s a workable proposition.
We counter the plummeting ambient temperature by respiring, digesting, which produces heat. We burn cookies for heat! And there are other strategies; for instance, we humans, birds, squirrels, rabbits, and others who are awake to see the snow can actively insulate ourselves with nests, and we can increase our collective body mass by huddling together.
Our feathers or hairs fluff out as we shiver, creating a larger pocket of warm air against our bodies—the same as fluffing a comforter. And shivering itself causes warmth, as the rapid contraction of muscles, kinetic energy, produces heat.
True mammalian hibernation is a subset of enderthermy, where the animal burns stored fat to stay alive during its long winter's sleep, but not enough to be active.
There is also a strategy called “regional heterothermy,” where an animal’s body permits its extremities to be colder than the core. To understand the problem, look, for example, at the Arctic hare, which is shaped like a ball, while an Arizona jackrabbit has long legs and ears. In this case, the jackrabbit’s body does a better job of casting off excess heat, while the hare conserves it.
But, in cold weather, heat loss in the extremities can be a serious drain on the body’s “core,” and there are more physiological mechanisms that combat this, allowing the extremities to be a different temperature, but within reasonable limits. One of these mechanisms is called the “rete mirabile” (miraculous net), which provides for a counter-current heat exchange. Generally speaking, in this arrangement, a big artery carrying nice warm blood from the core of the animal passes down the middle of the appendage; surrounding that artery are a network of veins returning the cooler blood back from the extremity. So the blood loses warmth while in the appendage but is warmed before being returned to the body.
In addition to the legs of terrestrial mammals (think especially of hooved animals like deer and horses), this circulatory arrangement is found in the flippers of marine mammals, as well as in the long legs of herons and other wading birds (which helps explain how they can walk around in ice-cold water, without screaming and dancing around in agony).
Wading birds are often seen standing on one leg in the cold water, with the other one tucked up against the body, so only one leg is getting cold. Then you also see birds tucking their bills under their wings, because inhaling cold, raw air can lose them more heat; it’s their equivalent of you wearing a nice wool scarf over your face.
4.
Finally, there are the organisms that simply pass away as summer closes. My beloved argiope spiders (and most other spiders and insects as well) slow down as the temperatures decrease. They can’t feed as quickly, and chances are, their prey items begin to dwindle, too. Being slow and clumsy increases the chance of being chomped by something else. (I think I told you that a big Chinese praying mantis is what did in our argiope by our front door.) (The mantis itself died shortly after, the top of its food pyramid.)
On the bright side for the late Mrs. Argiope, she had left behind some nice egg cases, whose hundreds and hundreds of spiderlings will emerge in spring, like pretty, delicate flowers, to bloom and grow into the next season.
Indeed, insects and many little flowers have a lot in common in wintertime; when conditions aren’t right anymore, when temperatures make them clumsy and rob them of food, when photosynthesis can’t obtain enough light, when their delicate tissues can’t withstand freezing—they simply wither. They die. It’s their seed, their eggs, or sometimes their pupae, that survive the winter in a state of suspended animation. These awaken like sci-fi astronauts into a new time, the “future,” with a fresh new world to explore, where they will experience the entire, wild adventure of life.
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But man . . . it’s seriously cold out there.
Feed your birds.
And pray for the rest of ’em.
(And it should go without saying: don't you dare leave your pets outside in this stuff.)
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