Cold

by Bill Streever

  A flock of migrating birds is more than the sum of the individual birds, and less. Free will seems lost. Some combination of instinct and memory and groupthink drives the beat of wings away from the cold and toward reliable food. Birds flew some of these routes before men hunted with stones. Many knew the sting of the nineteenth-century market hunters, feeling the flak sent up from shotguns mounted on the bows of punts like batteries of antiaircraft guns strung along the nation’s flyways. Birds have seen the lights of cities flicker on. They have run into buildings that grew out of prairies. Resting in trees or on the ground, birds have learned of the dangers of house cats: one hundred million birds feed themselves to tabbies every year.

  Most recently, birds have discovered microwave communication towers, running into them at full migratory speed, no doubt thinking, This wasn’t here last year, just before abruptly stopping beak-first, skull-second, bones shattered, then falling to the ground, migration finished, game over, lights out.

  It is October twentieth and fifty-four degrees in Anchorage. In my absence, the snow has crept farther down the mountains, but for now it is still above the streets and houses and office buildings of the city. I am disappointed. It has been too long since I last felt snow under my feet. I drive to Flattop, a little mountain just outside town with what is reputedly the most hiked trail in all of Alaska. I am here to walk in snow, but also to look for ground squirrels, thinking that this might be my last chance to see them before they hibernate.

  Within ten minutes of the trailhead, at something like twenty-five hundred feet above sea level, I see hoarfrost, water vapor frozen into intertwined white crystals on the surface of the ground. The willows along the trail are nearly leafless, and the crowberries hang from stems that have turned from rich green to dry reddish brown. A bull moose forages on the slope beneath the trail. Soon the moose will find its way into the valleys, where it will stand in the winter cold, gnawing bark from shrubby trees. It will lose its antlers. When the leaves are gone and there is nothing to eat but bark, moose might spend six hours feeding and twelve hours ruminating. Eating more to stay warm is pointless, because they cannot digest their food as quickly as they can feed. They lose weight. In a bad winter, many will starve. But it must be a very bad winter. Their metabolic rate does not increase until temperatures drop below minus twenty. As often as not, their problem is staying cool. Winter-acclimatized moose are known to start panting as temperatures rise toward the freezing point.

  Within twenty minutes of walking, there is snow on the trail — white dust scattered on the surface of dark mud and caught in the leaves of crowberries. Here, at twenty-six hundred feet above sea level, it is ten degrees colder than at the trailhead. The clouds open for a moment, and the sun bathes Anchorage and Cook Inlet. I pull on a hat. A few minutes later, the clouds close up again, and big slow-moving snowflakes drift down, sticking to my shirt. At around twenty-eight hundred feet, I scan a slope of splintered bedrock and ice-shattered boulders, looking for ground squirrels. They are common here, among the rocks. In summer, they stand on their hind legs, imitating prairie dogs, watching tourists panting and struggling up the mountain. The ground squirrels will overwinter in burrows hidden beneath the rocks. It is in these burrows that they fall deep into hibernation. It is here, during winter, that their body temperature drops to just below the freezing point of water, close to thirty degrees. The ground squirrel’s blood is more than ten degrees colder than that of a hibernating chipmunk. In the laboratory, a ground squirrel blood sample would freeze at thirty-one degrees, but within their frigid sleeping bodies, ice does not form. Their blood is super-cooled — it is below the freezing point, yet not frozen. Supercooling occurs when there are no nucleation sites, no place for nascent ice crystals to get a toehold. Formation of a single ice crystal in the supercooled blood of a hibernating ground squirrel could flash freeze the little beast. The ice crystals would rip through cell membranes. The squirrel would die.

  Here, too, in the burrows beneath these rocks, as often as every two weeks through the long cold of winter, the squirrels warm up. They are no different from other hibernators in that they need their sleep. They burn away fat reserves to warm up enough to sleep. An electroencephalogram of a cold squirrel shows a quiet brain, but when they warm up enough to sleep, the same electroencephalogram will show the patterns of dreaming. Dreaming of what? Of spring? Of succulent shoots and fresh flower buds? Of mating? For about a day, they warm up, and then they cool off again, quickly dropping to near freezing, and then somehow maintaining their body temperature at just above freezing. How do they do it? How does a nearly frozen brain, its neurons less nimble than cold molasses, tell the little rodent that it is time to wake up? No one knows.

  In the cold air, I can hear Anchorage traffic. The combination of cold air and snow plays tricks with sound. If I turn my head slightly, or move a bit, the traffic noise is replaced by the sound of fast water coursing through the south fork of Campbell Creek, some eight hundred feet below me. Sound travels quicker through cold air than warm, but snow muffles sound. Between traffic and flowing water, I listen, too, for golden-crowned sparrows, for their tweeting song that sounds like “three-blind-mice, three-blind-mice,” high-pitched and repetitive. But the little birds are gone, headed south toward Washington and Oregon and, for some, as far as California and the Baja peninsula. I check my thermometer. At this elevation, somewhere close to three thousand feet, it is thirty-four degrees. It will drop well below freezing tonight. There are no squirrels. They are already curled up in their burrows, bivouacked. It is snowing hard now. The city is lost behind a curtain of snow, and the mountains around me appear through a fog of slow-moving white flakes.

  The last few hundred feet of the mountain are as steep as the steps of a lighthouse. The trail this high is covered with snow, and under the snow, from the trampling of other walkers, is ice. Eventually, I am clambering, grabbing rocks to avoid slipping. The snow — its coolness, but also its texture, crunchy but soft — feels good on my hands. Just below the summit, my right foot slips, and then my left, and it is only my hands that keep me from falling. That is how it is with snow-covered ice. Blink and what feels like firm footing becomes slicker than oil. My toes find a purchase, and I look down. I would not die if I fell from here, but I would be bruised and maybe broken. My fingers are numb. I have no need to crawl up the last twenty feet to the summit, so I turn and inch my way downward. Thin snow on top of ice has left the trail so slippery that I am trembling now and crab-walking downward. In places, I slide shamefully along on my behind. The snow eases for a moment, and the city materializes in the growing twilight. Through the lessening snow, Cook Inlet glows orange and blue with steeply angled rays of evening autumn sun.

  NOVEMBER

  It is November fifth in Palawan, an island in the Philippines, 500 miles north of the equator and 250 miles south of Manila. It has dropped below twenty degrees in Anchorage, and the North Slope has touched zero, but here in Palawan, it is eighty-two degrees. My migratory compass has, for the moment, acted birdlike, bringing me to warmer climes. Somewhere here on the island, the arctic warbler should be overwintering, just arrived from Alaska. If these birds are here, they are likely worn out, still recovering from a self-propelled migration, adjusting to the heat, coping with a new suite of predators, and recuperating from their own version of jet lag. But I see none of them. Instead, I see resident birds — a tropical kingfisher gliding low over blue water, a slender white-bellied woodpecker working the trunk of a coconut palm, a Philippine sea eagle riding thermals up the side of a limestone cliff. These birds will never know the feeling of snow between their toes. They will never know sea ice.

  Underwater, I hold my breath and listen. The water temperature hovers around seventy-two degrees, and the sea is alive with the clicking of shrimp, sounding something like grains of sand and gravel awash in surf. In the distance, I hear the motor of a fisherman’s banca, a thin canoe-like craft with twin outriggers for stability and a jury-rigge
d gasoline motor thumping through the waves. My companion says she can hear damselfish. I listen again. And there it is, a low-frequency grunt, an unmistakable burp just at the edge of my hearing. And then another answering the first. Now, my ears attuned to the right frequency, I hear a chorus of burps, one after another, burp after burp maybe saying something meaningful in damselfish-speak or maybe just the sound and the fury of three-inch reef fish.

  These little fish are stuck here in the tropics. They die in colder water. A near relative, the blacksmith, which broke away from its tropical cousins some nine million years ago, lives as far north as Monterey Bay, California. The difference between the two? Enzymes. Enzymes are protein molecules, but unlike other proteins, enzymes are there to encourage reactions important to life. Bring two molecules together without an enzyme, and they may eventually react. Bring the same two molecules together on the surface of an enzyme, and a millisecond later they have reacted. To say that enzymes speed up reactions would be to downplay their importance. They rocket reactions into hyperdrive, increasing reaction rates several million times. And they are selective. They bring together certain molecules but ignore others. More than four thousand biochemical reactions are known to be mediated by enzymes. Enzymes are nothing less than the linchpins of metabolism.

  But here is the catch: different enzymes work best at different temperatures. Take a damselfish enzyme that works best in the Philippines, make a few subtle amino acid changes across nine million years of evolution, and you have an enzyme that works best in northern California. Molecular Biology and Evolution, an academic journal, reports on the differences between damselfish and the related blacksmith: “Enzyme adaptation to temperature involves subtle amino acid changes at a few sites that affect the mobility of the portions of the enzyme that are involved in rate-determining catalytic conformational changes.” Sketches of fish enzymes, twisted and retwisted ribbons spiraling across the page, show the difference between the enzymes of the tropical damselfish and the blacksmith. The difference as illustrated is not profound. The difference in the real world is the difference between life and death.

  Anything affecting temperature affects the efficiency of enzymes. So do certain poisons. Temperature — the wrong temperature — acts like poison. It is not so much an issue of cold taking a single enzyme out of commission as one of cold disturbing the synchronous behavior of an orchestra of enzymes, leaving one playing too slowly, another too fast, and another barely playing at all, and in the end reducing the symphony of metabolism to the cacophony of malaise and death.

  Temperature limits the ranges of species. Tropical damselfish are tropical not because they like warm water so much, but because they need warm water. By impairing enzyme performance, cold water kills tropical damselfish, or slows their growth or stops them from reproducing. The same is true for the corals out here, and the sponges, and the clicking shrimp. Move to the north or south, and the corals and sponges and shrimp are gradually replaced by other species with other enzymes that work at other temperatures. First one species drops out, then another, then another. They all play the odds, balancing enzyme efficiency against other risks. The enzymes of a fish may work best at eighty-one degrees, but if the enzymes of its predators work best at eighty-one degrees, it may be better off a bit farther north. It might do the same thing to avoid competitors. It may be better off taking its chances in places where the occasional cold snap could wipe it out. Or it may be better off warm-blooded, fighting off the cold outside to keep those enzymes at peak efficiency. It would need more food; it would need more insulation; it would need adaptive behaviors and down jackets and baseboard heat and maybe an electric blanket. But it could live almost anywhere, while these damselfish are condemned to the tropics.

  When I tire of listening to grunting damselfish, I stand in the water. Facing shore, I look at coconut palms growing just beyond white sand. Farther back, in the hills behind the beach, macaques play in jungle branches. I turn to watch the swells coming in from the South China Sea. They break on the reef face. A surge of water, the remains of a broken wave, advances across the shallows, then retreats, leaving white foam behind to slip slowly back. The sun hangs low on the horizon. At this latitude, sunset comes quickly. I can almost see the sun move as it sinks into the sea. This is the same sun that will rise in just a few hours over my home in Alaska, but there it will rise slowly, seeming to skim along the horizon, reluctant to show itself to snow-covered black spruce and frozen tundra.

  There was a time during the history of the science of ecology when a few obvious observations could become a rule. Today ecology relies on advanced statistics, on multivariate models and randomization techniques and the use of Greek letters in place of actual words. But a hundred years ago, it relied on narrative descriptions and observations. People like Karl Bergmann — working in the 1840s at the same time that Louis Agassiz was studying glaciers — noticed that animals in cold climates were bigger than their warm-climate cousins. Siberian tigers were bigger than Bengal tigers, and Bengal tigers were bigger than tigers in equatorial jungles. Northern badgers were bigger than southern badgers. White-tailed deer in Michigan were nearly twice the size of those in Nicaragua. Somewhere along the line, Bergmann’s realization that cold-climate mammals were often bigger than their warm-climate cousins became known as Berg-mann’s Rule. Working with the chaos of nature, ecologists cling to patterns. They ignore or excuse exceptions. Most ecologists were not troubled by the fact that Arctic brown bears were far smaller than the brown bears of southern Alaska. An animal in a northern climate, the explanation goes, should be bigger, because a bigger animal presents less surface area for every ounce of weight. As the size of a cube or a sphere or an irregular shape — the shape of a bear or a moose or a caribou — increases, its surface area increases less than its volume. For every pound of body weight, for every ounce of muscle and fat and liver and lung and heart, a big animal has less skin exposed to the cold than a small animal. A big animal holds on to its heat more effectively than a small one, all else being equal.

  Bergmann’s Rule is not so much a rule as a pattern. And there are other patterns. Here you are in an oak forest, and a bit farther north you are in a spruce forest, and a bit farther you are in a treeless plain with frozen ground. These are the biomes of ecological maps of the world. The oak forest is temperate deciduous forest, the spruce forest is taiga, and the treeless plain is tundra. Biomes have clear boundaries on maps of the world, but the boundaries blur on the ground. The taiga fades to scrubby spruce trees, their enzymes failing them and their roots struggling to find a way through frozen soil. The spruce trees become more scattered. Seedlings might take hold for a year or two in a patch on the south-facing slope of a hill or along a river, then die back when a brutally cold, dry gale howls in from the north, blowing them over or sucking away the moisture that keeps them alive or sand-blasting them with crystals of wind-borne ice. Or the boundary might move way north, as it would have during the Medieval Warm Period, and then south, as it would have during the Little Ice Age. Stragglers, unable to reproduce in current conditions, their flowers not maturing or their pollinators no longer present, might hang on long after the climate has changed, little islands of out-of-place spruce or pine or oak trees.

  The ranges of species go where the species work best, destined by the character of their enzymes, destined by how well their enzymes work at different temperatures. But also: Who will graze on my leaves? Who will eat me? Whom will I eat? Is there space for my nest? Is the soil right for my burrows or my roots? Who will drive me away? Puffins became scarce around Britain after 1920 not because of the air temperature, but because the fish they ate followed a shift in water temperature. The birds followed the fish. When water temperature shifted again around 1950, the fish returned, and with them the puffins. The lives within the biomes are interwoven, and if one species can go no farther because of the temperature, it may affect another species, and another, and another, until it appears as though there is some d
efinite boundary and that everything responds in concert. But zoom in on the map, look a little closer, and the boundaries blur. Brown bears live in tundra and taiga and temperate deciduous forest. Caribou migrate across biome boundaries. The red fox, the tiger, the wolf, the wolverine, and the raven all cross biome boundaries as if they did not exist, as if they have never read an ecology textbook or studied a biome map.

  During the Little Ice Age, the cod fishery in Iceland — a fishery that had been active for centuries — failed as certain fish moved south to warmer water. The Dutch prospered when cod appeared in the North Sea. The range of man, of Homo sapiens, changed, too. Eskimo hunters showed up in Scotland. Iceland’s population fell by half, and the Norse abandoned settlements in Greenland, or their inhabitants simply died. And then the weather broke. The Little Ice Age gave way to a warming trend, perhaps helped along by carbon dioxide dumped into the air from the fires of man — first wood, then wood and coal, then wood and coal and oil, all burning at once, all contributing to the slow construction of a global greenhouse. Bering headed north, along with De Long and Greely and Peary and Cook. Amundsen and Scott and Shackleton headed south. Some of them retreated alive, while others perished like the Norse in Greenland, like spruce trees rooted too far north, too far into the polar zones, too far into the cold, and buffeted by deadly winds.