Cold (13 page)

Hibernation, in its broadest sense, is winter inactivity. It is a way of bypassing periods of food scarcity, of skipping those
times when the calories needed to stay warm exceed the calories that can be reliably gathered. Black bears, preparing for
hibernation in the late fall, can gain thirty pounds in a week while for the most part eating nothing but berries and foliage
and maybe insects. Brown bears — grizzlies — can pick up eight inches of fat, becoming, according to official information
published by the Alaska Department of Fish and Game, “waddling fat” just before hibernation. Then winter hits. Food availability
diminishes, snow slows down movements of foraging animals, and cold burns calories. Animals preparing for hibernation stop
eating. They repair to a den — maybe a hollow tree, a brush pile, a crack in the rocks, a corner in a cave, a pit dug into
the side of a hill. A black bear was once found denning in a tree hollow ninety-six feet aboveground. Grizzlies have been
known to tunnel nearly thirty feet into the earth. For polar bears, only pregnant females hibernate. In Alaska, the polar
bear den is a snow cave, dug on land or on the sea ice, sealed over and invisible after the next real snow.

The bear curls into a ball, its head resting between its forepaws, its back to the cold. Heart rate drops. Breathing slows.
The digestive tract shuts down for the winter. Blood concentrates in the head and upper body. Body temperature drops nine
degrees. The bear lives off its summer fat. Cholesterol levels skyrocket, but without causing heart problems. The bear will
not urinate for months. Urea, normally jettisoned in urine, is reabsorbed through the bladder wall and processed back to amino
acids and proteins. Likewise, calcium leaking from bones into the blood is recycled.

Certain Native Americans thought of den emergence as a form of rebirth. Males usually come out first. Females with cubs follow.
Emergent bears might appear stiff, hobbling about like old men. They stretch. They sniff about. They yawn and scratch. They
are thirsty but not immediately interested in food. When their appetites return, they dine first on roots and herbs, restarting
a dormant digestive process. The mighty polar bear, often thought of as pure carnivore, has been seen pawing through the snow
to feed on frozen salad just outside its den. Bears at emergence, at rebirth, may weigh as little as half their autumn weight.

It is not just bears that hibernate. It is ground squirrels and chipmunks and groundhogs and raccoons and skunks and prairie
dogs. Some, such as raccoons and skunks, hibernate softly, like bears, in a deep stupor but without the dramatic body temperature
drops of ground squirrels and groundhogs. Some hibernate alone, others in groups. Groundhogs — variously known as woodchucks,
marmots, and whistling pigs — sleep in family groups. All wake occasionally to warm themselves and to drift into a softer
sleep, a nonhibernating sleep that allows them to dream.

Birds, for the most part, migrate. Until the 1940s, scientists believed hibernation to be as unbirdlike as carrying an umbrella.
It was then that biologist Edmund Jaeger, wandering in the Chuckwalla Mountains of the Colorado Desert, watched poorwills.
Poorwills are nocturnal birds, seven inches long, that feed on flying insects. “Where do they go in the winter?” Jaeger asked
a Navajo boy. “Up in the rocks,” the boy replied. The Hopi, too, knew the poorwill, and in their language called it “the sleeping
one.” In winter, Jaeger found what at first seemed to be dead birds in the rocks, but when he picked them up, they flew away.
He watched one that stayed in torpor for eighty-five days. He pushed a thermometer up the cloaca of a torpid poorwill and
found its body temperature close to that of the air. Its pupils did not react to light. He found no heartbeat. The bird did
not seem to breathe. But in spring it flew away. Its awakening, its rebirth, coincided almost perfectly with the reappearance
of flying insects. In a 1949 paper, Jaeger wrote, “I take it as evidence that the bird was in an exceedingly low state of
metabolism, akin, if not actually identical with hibernation, as seen in mammals.”

Later, biologist Jon Steen watched titmice and finches. With enough food, the birds shivered through the night, their feathers
puffed up, their heads tucked under their wings, their aura, to the extent that birds project an aura, pathetic. But hungry
birds entered a nightly torpor. Their body temperature dropped. They have since been called “daily hibernators.” Biologist
and author Bernd Heinrich has written, “Physiologically there is no distinction between hibernation and daily torpor.”

Reptiles and amphibians are not exempt. Snapping turtles — air-breathing reptiles — can lie under the mud beneath the frozen
surfaces of lakes for more than four months at a stretch. The Manitoba toad of Minnesota summers near flooded depressions
left behind by Pleistocene glaciers, but in winter it hops upslope and burrows into gopher mounds. Two University of Minnesota
biologists tagged hundreds of toads with radioactive chips and followed them through the winter. The toads, underground and
without food, in amphibian semistupor, gradually burrow deeper through the winter, staying ahead of the ever-deepening frost
line. Somewhere around four feet down, they stop digging. By spring, their body temperature is just above freezing, not much
warmer than that of a hibernating ground squirrel. But unlike the ground squirrel, the toad will not shiver itself back to
warmth. It will have to wait for its tunnel to warm, and then it will crawl out of its burrow, looking for sun.

The wood frog is to the Manitoba toad as Maine is to Florida. The wood frog’s habit of overwintering frozen, with ice in its
veins and between its cells, was not understood until 1982. Naturalist John Burroughs, walking in the woods of New York in
December 1884 — nearly a hundred years earlier and nearly seven decades after the Year Without Summer — heard a frog calling
from beneath the leaves. He lifted the leaves. “This, then,” he wrote, “was its hibernaculum — here it was prepared to pass
the winter, with only a coverlid of wet matted leaves between it and zero weather.” Burroughs at first believed this to be
a predictor of an easy winter. “Forthwith,” he wrote, “I set up as a prophet of warm weather, and among other things predicted
a failure of the ice crop on the river…. Surely, I thought, this frog knows what it is about, here is the wisdom of nature.”
The frog, he believed, would burrow into the ground if a cold winter was ahead. But he was wrong. Two feet of ice formed on
the nearby Hudson River, and it was still bitterly cold when Burroughs went back to look for his frog in March. The leaves
of the hibernaculum were frozen. He peeled them back, and beneath he found frozen ground. Between the frozen leaves and the
frozen ground lay his frog. “This incident convinced me of two things,” he wrote, “namely, that frogs know no more about the
coming weather than we do, and that they do not retreat as deep into the ground to pass the winter as has been supposed.”

When handled, Burroughs reported, the frog blinked. In this he was mistaken, for frozen frogs do not blink. The idea that
a frog could spend the winter frozen was so outlandish that Burroughs appears not to have considered it. He saw what he believed
because he could not believe what he saw.

Flash forward one hundred years to when a physiologist named William Schmid found a wood frog under the winter leaves in Minnesota.
The frog was frozen. Schmid thawed it out and watched it come to life. In 1982, he published “Survival of Frogs in Low Temperature.”
So far, four frog species are known to overwinter in a frozen state. To be clear, these are not frogs that are cold, but frogs
that are literally frozen. Pick them up, and they are as hard as ice. They are, in fact, largely ice. Almost two-thirds of
their body water may be frozen. Ice crystals form between their cells and throughout their body cavities, but the cells themselves,
protected by high concentrations of glucose, do not freeze. In this state, the frogs can survive body temperatures as low
as eighteen degrees.

Bugs are stranger than frogs. Tent caterpillar eggs are full of glycerol, a form of alcohol that acts as an antifreeze. Caterpillars
— my Fram and Bedford — simply freeze solid. Take an African desert fly, dry it out, throw it in liquid helium at temperatures
below minus 450 degrees, warm it up, and pour some water on it, and it will demonstrate what it is to be a survivor.

And there is the trick of supercooling. Water, it turns out, has a sharp and consistent melting point. Warmer than thirty-two
degrees, ice becomes liquid water. But chill water below thirty-two degrees, and it may still be liquid water. In this supercooled
state, the liquid is unstable. Add a speck of dust or a snowflake — nucleation sites for ice formation — and ice crystals
will grow. That, though, understates the process. Supercooled water, once it goes, goes quickly. It flash freezes. The ice
crystals blossom. They explode into being. The trick to survival through supercooling is to avoid anything that might trigger
flash freezing. To flash freeze is to die. Yellow jacket wasp queens latch onto the underside of a leaf or a piece of bark
and then hang suspended, their body temperature dropping as low as four degrees. Supercooled, they do not freeze. But tap
them, or let a snowflake hit them from above, or a drop of water, and they turn to ice.

Bear biologist Lynn Rogers was walking one day in January. Quite possibly, he had passed the burrows of toads earlier that
day. He likely had trod past frozen wood frogs. He certainly would have been in the company of insects with antifreeze in
their tissues, of frozen insects, and of supercooled insects. Then he crawled into a bear’s den. “On January 8, 1972,” he
wrote,

I tried to hear the heartbeat of a soundly sleeping five-year-old female by pressing my ear against her chest. I could hear
nothing. Either the heart was beating so weakly that I could not hear it, or it was beating so slowly I didn’t recognize it.
After about two minutes, though, I suddenly heard a strong, rapid heartbeat. The bear was waking up. Within a few seconds
she lifted her head as I tried to squeeze backward through the den entrance. Outside, I could still hear the heartbeat, which
I timed (after checking to make sure it wasn’t my own) at approximately 175 beats per minute.

It is October thirteenth and thirty-six degrees in central Pennsylvania. A Friday the thirteenth cold front, invading from
the northwest, jumping the Canadian border without hesitation, decimated yesterday’s T-shirt weather. The front dumped two
feet of snow near Buffalo, New York, 150 miles from here. The
Washington Post
ran a photograph of a Labrador retriever bulldozing through the snow, its legs invisible beneath the white stuff, its nose
iced over, the look in its eyes one of joyful confusion. The
New York Times
ran a front-page color photograph of cars buried in snow and people in winter coats, shoulders hunched, walking away from
the camera, subliminally headed south. In Minnesota, the same weather system dropped temperatures to twelve degrees. It is
not supposed to be twelve degrees in October, not even in Minnesota. “Don’t forget the School Children’s Blizzard,” the weather
is saying. “Remember Greely. Remember who is calling the shots.”

Officially, I am here for a seminar on underwater sound, the sort of educational opportunity that only a large university
can offer. Unofficially, I am far more interested in learning through experience and observation. I want to learn more about
cold and to see firsthand how temperate zone students respond to it. I drive across the Pennsylvania State University campus.
The students are slimmer than those in Fairbanks, and clean-shaven: more primped, less insulated. Their warm clothes are formfitting,
lacking the space underneath for three sweaters. In general, the students here are less prepared for an ice age, but at least
one of them, graduated now and moved on, was a cryophile, a lover of cold. While here, he learned of a place just outside
town known variously as the Barren Valley, the Scotia Barrens, and just the Barrens. With his roommate, he nailed a thermometer
to a pine tree in the heart of the Barrens. The two of them drove the four miles out from campus once a month. “It is amazingly
quiet, amazingly clear, and amazingly cold,” he once wrote. When it was thirty degrees on campus, it was eight degrees in
the Barrens.

Below-zero dips in temperature occur thirty times more often in the Barrens than on campus, and below-freezing temperatures
occur twice as often. In the daytime, the Barrens warm up. By midafternoon, the Barrens are as warm as the campus. But at
night, temperatures plummet.

The area, a narrow valley between steep hills, was called the Barrens because the soil was too sandy to support productive
farming, a common naming practice. It was mined for iron ore late in the nineteenth century. The forest that had stood there
was cut down and the wood turned into charcoal. The sandy soil was exposed. Scrubby plants grew into sparse patches of trees.
Today houses encroach on the Barrens, but the heart of the place is owned by the state and managed for game. Heat escapes
from the dry, sandy soil as soon as the sun dips below the hills. Cold air tumbles downhill into the valley and settles in
for the night. A temperature of forty below was once measured in the Barrens — forty below zero in central Pennsylvania.