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Beringia was inundated roughly eleven thousand years ago, as the glaciers melted and the seas rose. But Asia and America still nearly touch here, a brushing kiss across the 50-mile-wid Bering Strait, and Beringia is still a way station of international significance. Some of the travelers come by sea: gray whales from Baja, salmon returning to their natal streams from the black waters off Japan and Korea, northern fur seals hauling out on the rocky islands of the Pribilofs. But far more journey by air. Many birds whose travels span the globe breed in western Alaska, and now, as summer faded to autumn, they were taking to the wind once more.

They were not leaving because the weather would soon turn cold—although it would, the raw, bone-deep cold of coastal Alaska, with its sea ice and wet snow and howling winds. Migration is, fundamentally, about food, not temperature; those birds that can continue to find enough to eat during the winter rarely migrate—why bother?—while those whose food supplies are seasonal must flee. Almost all of the more than five hundred North American species that migrate depend on weather-sensitive food supplies—the ducks and wading birds whose marshes are sealed with ice, for instance, or the insectivorous songbirds that can’t find bugs in a December snowstorm. Seed-eaters are less likely to migrate than insect-eaters and tend not to go as far when they do; they can find plenty of weed seeds in North Dakota in January, but for flying insects a bird must travel at least to the Gulf States, or all the way to the tropics.

Behind me, a small cove lay in the protective lee of the bluff. Windrows of dead eelgrass formed thick, snaky ropes at the high-water mark, black against the oily gray of the mudflats. Flocks of shorebirds were feeding there with restless energy—scurrying, probing, poking into the rich tidal muck for small invertebrates. Most of the birds were dunlin, small sandpipers with drooping bills, many still in breeding plumage, with reddish backs and black bellies, as though they’d squatted in soot. Every few minutes, responding to some silent signal of alarm, they would leap into the air, wings flashing white, then twist and circle to earth again to resume foraging.

Migration is not the simple, north-to-south-and-back-again affair that most of us assume, and the shorebirds feeding on that mudflat were a perfect example. Dunlin breed in much of Alaska and the Canadian Arctic, but they form three distinct populations, each with radically different migration routes. Those that I was watching were probably of the subspecies pacifica, which nests in this part of southwestern Alaska and travels relatively short distances along the coast, stopping anywhere from the southeastern Alaskan panhandle to Baja California. Dunlin that nest in the central Canadian Arctic, on the other hand, migrate overland to the southern Atlantic and Gulf Coasts of the United States. And those that breed in the Northwest Territories and northern Alaska cross the Bering Strait to Siberia, where they join Russian dunlin and migrate on to eastern China, Japan, and Korea.

Among the masses of dunlin were a number of other species of shorebirds, each laying on fat before departing for far-flung destinations. Rock sandpipers, matching the gray volcanic stone, would barely budge; although some would travel to California, many would pass the wet, gloomy winter right here. Least sandpipers no bigger than sparrows, like little, buffy windup toys, would skirt the coast to South America. Among them were two Pacific golden-plovers, the color of hand-worn brass, which might take one of two routes from Alaska. Some cross the Bering Strait and follow the Asian coast, finally veering southeast to Australia or the Pacific islands. Others fly southwest across the open ocean to Hawaii, and then on to the islands of the South Pacific; some apparently make the flight to the Marshall and Line Islands—a thousand miles south of Hawaii, and a trip of nearly 4,000 miles—in a single, nonstop flight. Others on the beach and flats that day would make similar migrations—the wandering tattler, a whimsically named sandpiper, which winters across much of the South Pacific, and the squat, piebald ruddy turnstone, which travels to Southeast Asia, Australia, and the islands of Oceania, as well as to the California coast.

This single acre of mud held examples of a dozen different migration strategies. Not far from the Pacific golden-plovers stood five American golden-plovers, close cousins distinguished (with difficulty) by their duller plumage and somewhat longer wings. They also breed in western Alaska and make equally epic trips, but in the opposite direction. First they fly east across Arctic Canada, feasting on its wealth of berries and insects before gathering in the Atlantic Maritime provinces; then they swing south, cutting across the western Atlantic nearly 2,000 miles to South America, eventually ending their trip in the grasslands of Argentina. Joining them on the pampas would be greater yellowlegs, which I had seen earlier in the day along freshwater streams flowing into Izembek Lagoon—graceful sandpipers with steely-gray plumage and colorful, ripe-lemon legs. From the muskeg forests of Alaska and Canada, the yellowlegs spill south each autumn across the hemisphere, but they take an overland route, some stopping as far north as the Pacific Northwest and mid-Atlantic coasts, but others pushing on clear to Patagonia.

Simply cataloging the avian wanderers that pass through western Alaska would be a lengthy chore. Virtually every black brant on earth stops at Izembek in autumn, feeding on the world’s most expansive eelgrass beds, before moving out in November for destinations as far away as Mexico. Most of the world’s emperor geese and Steller’s eiders, the latter a threatened species, congregate at Izembek in the fall; the geese move on to the Aleutians for the winter, but the ducks stay put in the sheltered lagoons.

In Beringia, a naturalist may find Hudsonian godwits bound for Tierra del Fuego and bar-tailed godwits headed for New Zealand; the small greenish songbird known as the Arctic warbler, which migrates to the Philippines, and Wilson’s warbler, yellow with a black cap, which flies to Central America. There are fox sparrows and golden-crowned sparrows that winter in Pacific coastal woodlands, and gray-cheeked thrushes that travel to the Amazon. All morning, I had been watching weathers, black-and-white songbirds that look like slim thrushes. They’ll join their Siberian brethren and fly to China and India, then continue on to eastern Africa together, while wheateaters from the eastern Arctic swing across Greenland and Iceland to reach western Africa by a European route, embracing the world in a wishbone of movement.

Out on the ocean around Izembek were more migratory wonders. The day before, an Aleutian gale had savaged the region, ripping even protected harbors to foam and fury. But from a sheltered nook overlooking Cold Bay, I had watched dark shapes skimming the waves, gliding on stiff, narrow wings that barely cleared the tops of violent whitecaps, to all appearances blithely unconcerned by the storm. These were shearwaters, fittingly named seabirds that spend virtually their entire lives on the open sea and that are among the world’s most accomplished migrants.

This particular species, the short-tailed shearwater, nests on small islands off the south coast of Australia and Tasmania. In April and May, at the conclusion of the breeding season, millions of shearwaters pour rapidly north along the western Pacific rim, taking advantage of the prevailing winds—across Oceania, past Japan, and into the Bering sea a month later, where they enjoy perpetual subarctic daylight and a rich food supply. They remain off Beringia until September, when they head down the American coast and across the central Pacific, again aided by local wind currents. The shearwaters return to Australia by late October or November, when observers along the coast of New South Wales have seen as many as 60,000 an hour going past, a torrent of birds fueled by the bounty of the Bering Sea. A short-tailed shearwater may cover more than 18,000 miles in a single year, carving a vast circuit on the Pacific, aided at each step of the way by the prevailing breeze—and yet they arrive back in Australia within the same eleven-day period each year.

Migrations like this leave us staggered; we are such stodgy, rooted creatures. To think of crossing thousands of miles under our own power is as incomprehensible as jumping to the moon. Yet even the tiniest of birds perform such miracles.

Some days before, four hundred miles to the east, I had been camping along the Alagnak River, a crystalline stream that roars out of the Aluetian Mountains of Katmai National Park. The Alagnak flows through open tundra and sparse spruce forests, its banks wrapped in thickets of alder and stunted birch; several times each day, I saw brown bears lunging into the river for forty-pound king salmon as large and red as fireplugs.

The streamside thickets were full of small birds, streaky and tinged with green—blackpoll warblers, five and a half inches long and weighing barely half an ounce each; you could mail two of them for a single first-class stamp. Warblers are largely a tropical family, either as permanent residents or winter migrants, but the blackpoll is the most northerly of the clan, breeding from western Alaska across the midsection of Canada to Hudson Bay, Labrador, and New England. It is also the most southerly in its wintering grounds, migrating as far as the western Amazon, giving it the longest migration of any North American songbird.

That would be remarkable enough even if the blackpoll took the most direct course. But it doesn’t. Instead, like the American golden-plovers, they cross first a continent, and then an ocean. As August wanes, most of the Alaskan birds travel east, across the boreal forests of Canada, all the way to the Maritime provinces and the coast of New England. For a blackpoll born on the banks of the Alagnak, that alone is a journey of roughly 3,000 miles. While some of them then hug the shore toward Florida, it appears that many blackpolls strike out south over the open ocean, departing the Northeast coast at dusk, ordinarily picking a night with a brisk, northerly tailwind after the passage of a cold front. They will need the help. For the next forty or fifty hours, the tiny songbirds will fly over the western Atlantic, wings buzzing at twenty flaps a second, climbing to altitudes of more than 5,000 feet. They will show up on weather radar as they pass Bermuda and the Greater Antilles, glowing green specks that form diffuse blobs on the monitors, like ghosts beneath the moon.

The warblers follow a curving track, steered and abetted by the wind. At first, the northwesterlies carry them out to sea, the wind’s push adding to the 20 miles per hour that the warblers can fly on their own. Midway, somewhere around Bermuda, the northwesterlies fail and the migrants come under the influence of the subtropical trade winds, which blow from the northeast. The tiny birds are shepherded back to the southwest, toward South America, finally making landfall along the coast of Venezuela or Guyana, an overwater trip of about 2,000 miles—a passage with no rest, no refueling, no water, during which each will have flapped its wings nearly 3 million times. “If a Blackpoll Warbler were burning gasoline instead of its reserves of body fat, it could boast of getting 720,000 miles to the gallon,” note two researchers.

Nor are the birds finished; although some blackpolls do winter in the rain forests of northern South America, others continue south as far as northern Bolivia and western Brazil, another 1,500 miles or so. Then, in April and May, they reverse course, making a less-spectacular but still daunting traverse of the Gulf of Mexico or the western Caribbean and returning to their breeding grounds via the interior of North America. In all, the elliptical round trip for an Alaskan blackpoll warbler may cover eleven or twelve thousand miles.

I have seen blackpolls crowding the spruce woodlands of coastal Maine in late September, the gathered multitudes of the northern woods, and heard their slightly buzzy call notes in the dark as they set off over the sea, staking their lives on an exhausting journey through storm-raked skies. Knowing that some have already come from as far as the Alaskan Peninsula is humbling. Yet, to my thinking, the most astonishing of all the migrants that leave Beringia each fall are two kinds of long-legged shorebirds, the bristle-thighed curlew and the bar-tailed godwit, some of which cross not just part of the Atlantic but the entire width of the Pacific Ocean.

From LIVING ON THE WIND by Scott Weidensaul. Copyright © 1999 by Scott Weidensaul. Used by permission of North Point Press, a division of Farrar, Straus, and Giroux, LLC.