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  Roughly a thousand years later, Nils Warnock and Bob Gill, a wildlife biologist at the Anchorage, Alaska, office of the United States Geological Survey (USGS), followed the flight of a bar-tailed godwit in a more leisurely fashion. From August 29 to September 7, 2007, they sat in their offices and watched their computers produce a line across a map of the Pacific Ocean—the flight path of E7, a baueri bar-tailed godwit whose surgically implanted satellite transmitter was sending signals to National Oceanic and Atmospheric Administration satellites 510 miles above Earth.

  Prior to her departure, E7 had been feeding voraciously on fingernail-sized clams, worms, and other marine invertebrates on the Yukon-Kuskokwim Delta along with tens of thousands of her kind. On August 29, she probably rose into the air throughout the day with other bar-tails, circling for several minutes, judging the weather, then settling back down. In early evening, a couple of hours before sunset, she rose into the sky and this time kept going, heading southeast. Within a few hours she crossed the Alaska Peninsula and headed out over the North Pacific.

  Gill hoped that the battery in her transmitter would last long enough to prove what he had long suspected about baueri's southward journey to New Zealand. Birds that migrate between northern and southern sites in the Pacific Rim—including baueri's close relative, the Siberian-nesting menzbieri race of the bar-tailed godwit—usually follow coastlines as they travel, stopping at shoreline mud flats along the way to rest and feed. To cross the Pacific Ocean, essentially a barren desert to land birds not adapted to landing and feeding on the water, would seem to be a fatal mistake. But rather than fly toward the Asian coast, E7, as Gill expected, turned south—toward open ocean. Three days later she was still flying above blue waters. Around noon, flying at an altitude of perhaps two miles or more, she must have had a beautiful view of the Hawaiian archipelago as she passed over it four hundred miles west of Honolulu. Two days later, she crossed the international dateline about three hundred miles north-northeast of Fiji. And then on the afternoon of September 7, E7 approached North Cape, the northernmost tip of New Zealand. She adjusted her flight path, and late that evening touched down at the mouth of the Piako River on the Firth of Thames, eight miles from where she'd been captured seven months earlier in the same mud-bottomed ponds where Gill, Warnock, and crew were now trapping more birds. She had flown for eight days—nonstop—covering approximately 7,250 miles at an average speed of nearly 35 miles per hour.

  This journey—the longest nonstop migratory flight documented for any bird—seems barely credible. "I just did a talk yesterday for some colleagues at the U.S. Geological Survey," Gill told me not long after E7 had been tracked to New Zealand. "And I showed these graphics of E7's flight and said, 'Okay, the flight is nonstop, no food, no water, no sleep as we know it, flying for eight days,' and there was just this silence in the room, and I could see their minds trying to wrap around this—as does mine. I try to be objective as a scientist, but this just..." Gill's sentence trailed off as he seemed unable to summon up the right word to describe his reaction.

  Although he may be at a loss for words to describe the wonder of the feat, Gill knows something of what makes such a flight possible. Like shorebirds in general, the godwit has a sleek, aerodynamic body and long, tapered wings that reduce drag in flight. Its endurance comes from the enormous reserves of fat the bird builds up in the weeks preceding migration, when it gorges itself on marine invertebrates, more than doubling its body weight until, as Gill has said, it looks like the Concorde when it takes off. Burned off dur ing flight, the fat yields more than twice the energy of comparable amounts of carbohydrates or protein. In addition, the godwit's body undergoes a remarkable change: its intestines and gizzard, which the bird makes little use of during migration, shrink, allowing more space to store fat.

  In his early sixties, with close-cropped white hair, Gill is the senior member of an international team of scientists analyzing the migration of godwits and curlews as part of a four-year project funded largely by the David and Lucile Packard Foundation. Gill's voice rises with enthusiasm when he speaks of the bar-tails, and here in New Zealand his spirit is all the more buoyant because he's wearing shorts and sandals; when he left Alaska two days ago, it was 10 below zero. Gill, Warnock, and their North American colleagues are working with a number of New Zealand biologists, among them Phil Battley of Massey University, as well as a local shorebird expert, Adrian Riegen. It is Riegen's van that Warnock and I are looking for in the darkness as we cross the cow pasture. There I pass on my godwit to more experienced hands.

  At the side of the van, Lee Tibbitts, one of the USGS Alaska crew, holds each godwit up into the light from Riegen's headlamp so he can measure the bird's bill with calipers. Female bar-tails are larger than males, and bill length is an easy way to distinguish the sexes. The team hopes to find several males large enough to carry an implanted transmitter so they can track an equal number of each sex. A transmitter weighs 25 grams, and the rule of thumb is that a bird should not carry anything that is more than 3 percent of its body weight.

  According to figures gathered over the past thirty years by the International Shorebird Survey, more than half of all shorebird species show evidence of serious decline. Some populations are dwindling slowly, some plummeting at a rate that, unchecked, will lead to their extinction in the not-too-distant future. Of all the taxonomic groups of shorebirds, the Numeniini (godwits and curlews) are the most threatened. Thirteen species of Numeniini exist worldwide. All but two of them—the black-tailed godwit of Europe and Russia and the Eurasian curlew of Europe and Asia—have received designations ranging from "critically endangered" to "species of high concern" by one or more world conservation organizations. With this tracking project, Gill and Warnock hope to learn more about the timing and routes of migration for several species of Numeniini, valuable information for future conservation efforts.

  Of the species that breed in North America—which also include the bristle-thighed curlew, long-billed curlew, Hudsonian godwit, marbled godwit, whimbrel, and upland sandpiper—the bar-tailed godwit is actually the most populous, with an estimated 1.2 million birds worldwide, 120,000 of which are the baueri race, which breeds mainly on estuaries in western Alaska. More than a million birds seems like a healthy population, but you don't have to look far to find a cautionary tale. One Numeniini, the Eskimo curlew, very likely exists in name only. The Eskimo curlew's population fell sharply in a few decades in the nineteenth century, dropping from hundreds of thousands of birds—perhaps millions—to a few individuals, the result of indiscriminate hunting and loss of the grasslands that they depended on during migration. Some estimate that anywhere from two dozen to a hundred Eskimo curlews may still be moving between their ancestral wintering sites in the pampas of Argentina and breeding territories in the far north, but this may be wishful thinking. The last confirmed record was a solitary bird shot in Barbados in September 1963.

  Godwits and curlews, like most shorebirds, are particularly vulnerable to habitat loss because they congregate in great numbers at a relatively few sites during migration, and many have restricted wintering sites as well. Understanding their migration is vital to any hope of developing effective conservation strategies to halt or reverse population declines. Although studies that began in the 1970s mapped the general migration routes for many shorebirds, it wasn't until birds were captured and outfitted with radio transmitters—and now satellite transmitters—that scientists began to see how individual birds used various sites.

  Warnock explains one reason this is important: "If you look at two sites, A and B, and site A has one hundred birds on it on day one, and site B also has a hundred birds on day one, and then you go back ten days later and both sites still have a hundred birds, you might think each site is equally important. But you don't know if it's the same one hundred birds or not. Site A may have a different one hundred birds each day—meaning one thousand birds have used it over a ten-day period—while site B has had the same one hundred bir
ds for ten days. Tracking individual birds can indicate how long a bird typically stays at a site. And that can tell you which areas are really most important."

  The Numeniini have significantly different migration strategies. Although the bar-tailed godwit is the ultimate long-distance migrant, the long-billed curlew, which breeds in the western United States, may travel only a few hundred miles from its breeding grounds to wintering sites. The bristle-thighed curlew is an intermediate-distance migrant, moving between Alaska and islands in the Pacific Ocean. Furthermore, the birds do not always follow the same migration paths in spring and fall. The baueri bar-tails, for instance, return to Alaska by a different route, and their northward journey is as interesting to Gill and Warnock as their record-setting southward flight.

  When they leave New Zealand in the spring, the birds head to the Yellow Sea. The coastline of this large, relatively shallow body of water between mainland China and the Korean Peninsula has 8,000 square miles of intertidal flats that support more than 5 million migratory shorebirds each year. There the baueri stop for five weeks or so to rest and feed. Then they launch out across the Pacific again on a beeline to their breeding territories in Alaska. Recent surveys have suggested that a great many of the baueri bar-tails stop at one site, the Yalu Jiang National Nature Reserve—450,000 acres at the mouth of the Yalu Jiang River, which separates North Korea from China.

  But fast-growing economies in this heavily populated region of the world are in direct conflict with shorebird habitat. Just down the coastline from Yalu Jiang, in South Korea, lies the Saemangeum estuary, a major stopover site for migrating shorebirds, including 30 percent of the world's population of great knots. In 2006, after years of court battles, the South Korean Supreme Court gave the government permission to complete a twenty-mile-long seawall separating the estuary from the Yellow Sea. The area's extensive tidal flats will thereby be "reclaimed" for agricultural land, and the water that remains will become fresh water from the rivers that feed the estuary. In time, the project will drain an estimated 154 square miles of tidal flats. Some of the new land can already be seen on photographs taken from NASA satellites. Where fertile intertidal flats existed, there is now stark white, barren land.

  It may get worse. Mark Barter, an Australian biologist who has worked in mainland China, writes that "80 percent of the significant wetlands in east and southeast Asia [are] classified as threatened in some way; 51 percent of these are under serious threat." Recently he told Gill of two reclamation projects on the Chinese coast of the Yellow Sea, each larger than Saemangeum. "The coastline of the Yellow Sea is just being assaulted," Gill says. It is tricky for Westerners to express outrage over this, considering that the ground we stand on is often the result of dams, dikes, impoundments, and other contrivances that have destroyed our own wetland ecosystems. "It's like San Francisco Bay a century ago," says Gill.

  So how safe is Yalu Jiang? How important is it really? How accurate are the surveys? If the need arises to make a case for Yalu Jiang, the bar-tailed godwits carrying satellite transmitters have provided irrefutable evidence: so far, the majority of satellite-tagged birds have stopped there.

  Wetlands are not the only threatened habitat. The winds—a "habitat" as tangible to the godwits as mountains, valleys, and wide-open plains—will certainly be affected by global climate change. The godwits "have evolved wind-sensitive migration strategies," Gill says. Presently, the birds must negotiate five different wind systems that rule different regions of the Pacific Ocean. Their departure from Alaska appears to be timed to take advantage of the winds created by storms that the Aleutian Low Pressure System sends to the Alaska coastline on an almost weekly basis during the period when godwits usually begin their journey. The birds ride the tailwinds from the back side of a storm for the first 600 miles or more, the winds boosting their speed up to 80 to 90 miles per hour.

  North of the Hawaiian archipelago the Northeasterly Trades blow toward the southwest. These "quartering" tailwinds (midway between a tailwind and a crosswind) push the birds along, but if they do not compensate for the westward wind flow, they will be blown far off course. The equatorial doldrums, a zone of little or no wind that sailors have always feared, neither help nor hinder the birds. At approximately 20 degrees south latitude, they face the Southeasterly Trades, quartering headwinds that they must fly against. And then, in the South Pacific, their fat reserves running low, they face more quartering headwinds as they enter a "conver gence zone." In recent years, studies that use computer models to predict how climate change will affect wind systems have come up with different results. But they agree on one thing: the winds will change. Perhaps the godwits will adapt. Or perhaps, over time, the winds will push them toward new, less agreeable wintering sites.

  At one in the morning on the second day of capturing godwits, I go with Nils Warnock and Jesse Conklin, a Ph.D. student at Massey University, to release two godwits that now carry satellite transmitters. We drive to a deserted beach north of the shorebird center rather than take them back to the crowded ponds. This will be a kind of post-op recovery room, where they will have some peace and quiet as they adjust to their surroundings. When the birds are released, they do not rush away, but stand motionless for a few minutes. Then, slowly, they walk off toward the sound of water lapping the shoreline.

  With the birds out of sight, we stand for a moment enjoying the night air. I look up, once again drawn to the starry sky. A poor student of astronomy, I'm delighted to recognize a constellation—Crux Australis, the Southern Cross. It is, of course, one of the most famous formations in the Southern Hemisphere, remarked upon by virtually every early explorer who sailed south of the equator. In a few weeks the godwits will rise into the air and leave behind Crux Australis for the cold northern skies of Ursa Major. On the tundra of the far north, they will breed and raise young, then move again to their staging grounds to prepare for the long flight southward. The adults will depart first, leaving behind the juveniles. A short while later, the young birds, guided by some deep baueri knowledge of the earth and wind and stars, will set off on a 7,000-mile journey to a place they've never seen—the land of the long white cloud.

  MATT RIDLEY Modern Darwins

  FROM National Geographic

  JUST TWO WEEKS BEFORE HE DIED, Charles Darwin wrote a short paper about a tiny clam found clamped to the leg of a water beetle in a pond in the English Midlands. It was his last publication. The man who sent him the beetle was a young shoemaker and amateur naturalist named Walter Drawbridge Crick. The shoemaker eventually married and had a son named Harry, who himself had a son named Francis. In 1953 Francis Crick, together with a young American named James Watson, would make a discovery that has led inexorably to the triumphant vindication of almost everything Darwin deduced about evolution.

  The vindication came not from fossils, or from specimens of living creatures, or from dissection of their organs. It came from a book. What Watson and Crick found was that every organism carries a chemical code for its own creation inside its cells, a text written in a language common to all life: the simple, four-letter code of DNA. "All the organic beings which have ever lived on this earth have descended from some one primordial form," wrote Darwin. He was, frankly, guessing. To understand the story of evolution—both its narrative and its mechanism—modern Darwins don't have to guess. They consult genetic scripture.

  Consider, for instance, the famous finches of the Galápagos. Darwin could see that their beaks were variously shaped—some broad and deep, others elongated, still others small and short. He surmised (somewhat belatedly) that in spite of these differences, all the Galápagos finches were close cousins. "Seeing this gradation and diversity of structure in one small, intimately related group of birds," he wrote in The Voyage of the Beagle, "one might re ally fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."

  This, too, was inspired guesswork. But by analyzing the close similarity of their g
enetic codes, scientists today can confirm that the Galápagos finches did indeed descend from a single ancestral species (a bird whose closest living relative is the dull-colored grass-quit).

  DNA not only confirms the reality of evolution, it also shows, at the most basic level, how it reshapes living things. Recently, Arhat Abzhanov of Harvard University and Cliff Tabin of Harvard Medical School pinned down the very genes responsible for some of those beak shapes. Genes are sequences of DNA letters that when activated by the cell make a particular protein. Abzhanov and Tabin found that when the gene for a protein called BMP4 is activated (scientists use the word "expressed") in the growing jaw of a finch embryo, it makes the beak deeper and wider. This gene is most strongly expressed in the large ground finch (Geospiza magnirostris), which uses its robust beak to crack open large seeds and nuts. In other finches, a gene expresses a protein called calmodulin, which makes a beak long and thin. This gene is most active in the large cactus finch, G. conirostris, which uses its elongated beak to probe for seeds in cactus fruit.

  In another set of islands, off the Gulf Coast of Florida, beach mice have paler coats than mice living on the mainland. This camouflages them better on pale sand: owls, hawks, and herons eat more of the poorly disguised mice, leaving the others to breed. Hopi Hoekstra, also at Harvard, and her colleagues traced the color difference to the change of a single letter in a single gene, which cuts down the production of pigment in the fur. The mutation has occurred since the beach islands formed less than 6,000 years ago.

  Darwin's greatest idea was that natural selection is largely responsible for the variety of traits one sees among related species. Now, in the beak of the finch and the fur of the mouse, we can actually see the hand of natural selection at work, molding and modifying the DNA of genes and their expression to adapt the organism to its particular circumstances.