FLATEY ISLAND, Iceland—When the days grew long, seabirds flocked to this hamlet on the edge of the Arctic to rear their chicks under the midnight sun.

"Kria," shrieked the terns, calling summer up from the slumbering ground. Black cliffs were transformed into snowbanks of white kittiwakes. Puffins whirred between land and sea. Murres plied the shoreline; fulmars patrolled the skies. Everywhere sounded their vibrant chorus.

These days, a few stubborn holdovers streak the sky and paddle the bay, but the legions are gone. The chicks have perished, and their bereft parents have returned to the sea.

Half of Iceland's seabirds nest on this low-lying volcanic outcropping and its neighboring islands in the deep west coast gash called Breidafjordur Bay. Flatey Island used to be covered with chicks snuggled inside rocky hillside burrows, under tall meadow grass, in nests strewn across headlands and shores.

"There were thousands! You could hear them," says Olina Jonsdottir, who has lived on this island with her husband, Hafsteinn Gudmundsson, nearly 50 years. She looks out her living room window, past the sheep grazing on knuckles of grass-covered lava, past the black basalt beach, to the few birds drifting over the water beyond. "You can't do that anymore. Now there are so few."

Iceland, circled by the food-rich currents of Atlantic, Arctic, and polar waters, is the Serengeti for fish-eating birds. Its rocky coast, hillocky fields, and jutting sea cliffs are breeding grounds for 23 species of Atlantic seabirds, hosting an indispensable share of Atlantic puffins, black murres, razorbills, great skuas, northern fulmars, and black-legged kittiwakes.

But the nests have gone empty in the past few years, and colonies throughout the North Atlantic are shrinking.

The suspected culprits are many. But the leading candidates are the array of profound changes under way in the world's oceans—their climate, their chemistry, their food webs, their loads of pollutants.

Warming oceans and earlier thaws are driving away the seabirds' prey; unleashing deadly, unseasonal storms; and knocking tight breeding schedules off-kilter. Mounting carbon dioxide absorption and melting glaciers are acidifying and diluting the aquatic balance, jeopardizing marine life and the creatures that depend on it for food.

View Images NG STAFF

Alarmed scientists have returned from fieldwork throughout the North Atlantic with sobering descriptions of massive chick die-offs and colonies abandoned with eggs still in the nests.

"Mass mortality of kittiwakes is evident," said Freydis Vigfusdottir, a post-doctoral researcher at the University of Exeter in Cornwall, England. "You can see in the late summer lots of 'chick pancakes' in the nest."

And in the Arctic tern colonies she's studied, "there are just dead chicks everywhere," she said. "Not only do you have to provide your field assistants with food and shelter, but also some psychological help after many, many days of collecting dead chicks."

On Flatey Island, the once-prolific terns haven't produced viable chicks in a decade. More than half of the region's black-legged kittiwake nests vanished over 15 years.

And on the Westman Islands off Iceland's south coast—home to the world's largest Atlantic puffin colony—breeding has been a "total failure" since 2005, according to the South Iceland Nature Center. The impacts are being felt throughout the country, where these clown-faced birds have been both a legally hunted delicacy and a national mascot. "Puffin watch"—news on how things are going in the burrows each summer—is as avid here as "volcano watch."

Similar trends are reported in Scotland, the Faroe Islands, Norway, and across the circumpolar north—the principal nursery for Northern Hemisphere marine birds. Most of the biome's species, the 2013 Arctic Biodiversity Assessment finds, are in decline.

Whole populations haven't collapsed—at least not yet. These hardy seafarers are long-lived, and millions of them still sail the North Atlantic. Normally, seabirds can withstand a few bad breeding seasons. However, reproductive failures have been going on for so long now that scientists say it's just a matter of time before the adults, too, are gone.

Now researchers are struggling to comprehend the catastrophic breeding failure and its implications for an ecosystem that is fundamental to the planet's health.

These days, a few stubborn holdovers streak the sky and paddle the bay, but the legions are gone.

The seabirds' plight "is a huge concern ... not just in the North Atlantic but also globally," Vigfusdottir said. The cold waters of the North Atlantic are a major driving force for the Earth's weather and among the most productive fisheries in the world, so the birds' problems could indicate trouble for the region's major industry and the global food supply.

These same problems are now being noted in wading birds like the redshank, shorebirds like the red knot, and other waterfowl in the northern United States, United Kingdom, and elsewhere.

"What is happening in Iceland, we see happening in so many other areas in the North Atlantic. And the fact that we're seeing them over such a wide area points to a common factor ... and that is climate change," said Aevar Petersen, a retired Icelandic Institute of Natural History ornithologist.

Winds and currents funneling pollution northward from Europe, North America, and China bring more bad news for seabirds preying high on the food web. Mercury is ubiquitous—and rising fast in some areas. Brominated flame retardants, perfluorinated coatings, pesticides, plasticizers, polychlorinated biphenyls (PCBs), and more are contaminating a variety of species and locations. And masses of chemical-laced microplastics could be released by melting ice sheets.

Seabirds "are critical for detecting changes that are happening even more rapidly than we suspected," said Jennifer Provencher, a doctoral student at Carleton University in Ottawa who examines colonies in Arctic Canada. "We are getting basically a year-to-year-to-year update of the health of the oceans and the health of the environment through these seabird studies."

It's likely all these threats are adding up, sounding a warning across the north, she said.

"They're alarm bells, in real time, of changes that are going off."

View Images Northern fulmars fly by Iceland's Skógafoss Waterfall. Iceland is a nesting nexus for fulmars, but breeding looks dismal again this year. Photograph by Wouter Pattyn, Buiten-beeld/Minden/Corbis

Puffin Prophecies

Thick-coated sheep bleat as Erpur Snaer Hansen trudges across their steep pasture overlooking the sea. This is Heimaey, one of the 15 volcanic stacks lying off Iceland's south coast that make up the world's most important breeding grounds for puffins: the Westman Islands. Hansen, a biologist with the South Iceland Nature Center, is Iceland's de facto puffin prophet: Twice a summer he rounds the country to tally eggs and chicks and announce whether the birds' breeding seems headed for success or another year of failure.

Hansen stops at a small, rocky hollow surrounded by a dome of wet grass. He dons dark goggles and, looking like a welder conducting a medical exam, snakes a flexible pipe with an infrared camera into the opening. Puffins nest underground, and this "burrow camera" lets him see inside without disturbing the birds.

"Nothing there," he says after a minute, and moves on.

The burrows should be bustling now on this July day: The Westmans are one of Iceland's three "mega-colonies." More than a million pairs of various seabird species nest here, including around 830,000 puffin couples. Puffins are loyal to their breeding grounds, returning to the same site year after year. The majority of the world's puffins breed in Iceland, nearly half of them here in the Westmans. The area is crucial to the birds' future.

But Hansen and colleague Ingvar Sigurdsson find burrow after burrow empty. If the chicks die, or the eggs don't hatch, adults leave the colony early and go back out to sea. "There hasn't been a proper chick production in 12 years now," Hansen says. And for the past nine years, hardly any have lived long enough to leave the nest.

Finally, success: A lone adult is at home. Sigurdsson pulls out a grunting bird with a parrot-like orange beak and lays it on its back. Black triangles stare up from its Kabuki-white face as Sigurdsson measures, draws blood, and plucks a few feathers before letting it scramble back into its burrow. From this, the researchers will determine the bird's health and diet, and try to learn where it's been going to feed.

Rising ocean temperatures are squeezing out the birds' main prey, pencil-shaped fish called sandeel. For hundreds of years, sandeel were abundant in these waters, providing the intense nutrition chicks need for quick growth in the short northern summer.

Warmer waters seem to stunt the sandeel's growth, Hansen says. Plus, more southerly fish, like voracious mackerels, are moving in. Puffin parents must forage farther and come back with less—or less—nourishing-fish for their young. These days, chicks starve, nests are abandoned, and increasingly, birds don't even bother to breed.

The sun is still high when the researchers call it quits that evening. Their arms are covered in mud, and on top of that, Sigurdsson wears the fishy smell of puffin guano. "Ja, we study the poo as well," Hansen says. But they've found no chicks this day, and very few adults. Hansen saw similar conditions almost everywhere on his puffin tours this summer.

This cycle has occurred before, Hansen says later, at his house in the quaint, 4,000-person town of Heimaey. His analysis of historic weather and puffin hunting records has linked population dynamics to a periodic warming cycle called the Atlantic Multidecadal Oscillation, or AMO. Repeatedly, waters around Iceland have warmed for a few decades, then cooled for a few, and seabird populations have slumped, then recovered. The current warming cycle began in the late 1990s. But this time, Hansen's research shows, things are different.

"If you look at the AMO cycle, it's trending upward," he says. Ocean temperatures already have climbed as much as 2 degrees Celsius—nearly 36 degrees Fahrenheit—surpassing previous cycles. And chicks are taking a far greater hit.

Even when the current warming cycle ends, around 2030, "it's not going to be that cold at all," Hansen says. "I don't want to be alarmist. But global warming is definitely felt here... It makes things happen fast, and the birds are suffering."

He frowns as he thinks about their future.

"I'm fearing it's not going to be pretty."

View Images A common murre cares for a rare chick on Langanes Peninsula. In Iceland, levels of PCBs and other contaminants are so high in murre eggs that people shouldn't eat them. Photograph by Cyril Ruoso, Minden/Corbis

"All Dead"

The scene is virtually the same on Flatey Island, 200-some miles to the northwest.

"Another terrible year," says Petersen, stepping through thigh-high grass dripping with recent rain to survey an Arctic tern colony. A dozen or so of the fierce black-capped birds wheel overhead.

"Normally, there would be hundreds of birds here," the ornithologist says. Now, "there may be a few chicks. But they probably won't make it." Petersen's been coming to this island to count and band birds for 41 years. Some summers, he and his colleagues have banded 800 fat, gray Arctic tern chicks.

"This year," he says, "we've done five so far."

Reykjavik artist Ragnar Olafsson also notices the difference. When he came here as a child, the sky was thick with terns dive-bombing anything that came near their nests. They aimed for the head and frequently drew blood.

"I was terrified! I wore two or three hats." Olafsson looks up at the scant white streaks in the gray sky, and rubs his head. Now he can go hatless.

The Arctic tern is another special bird to Icelanders, who see its arrival as a sign that the long, dark winter is over. The bird is revered for its astonishing migration—flying from the Arctic to the Antarctic and back every year, nearly 50,000 miles. "Everybody knows it. Everybody likes it," says Petersen. "People used to say that it always came on the 14th of May to the pond in the middle of Reykjavik. There used to be a colony there. But no longer."

Petersen is here with an international group of researchers looking into what's going wrong with the seabird colonies in Breidafjordur Bay. The area is a nesting nexus for a variety of species, and breeding looks dismal again this year for kittiwakes, fulmars, puffins, and murres as well as terns.

This is the tenth year in a row that tern breeding has been poor, Petersen says, parting grass to look for the white streaks that are telltale signs of a nest. Just a month earlier he had seen around 200 terns in this same spot getting ready to nest. Now, "there are hardly any chicks around," he says.

"This is what we are seeing in the whole of Flatey," Petersen adds, "and further afield."

As in the Westmans, the birds' preferred prey seems to be in short supply, and the researchers are attaching geologgers to record their foraging trips. In the evening, the group motorboats out to a small island with a lighthouse. First up for tagging is an angry northern fulmar, spitting a foul-smelling orange glob of stomach oil at British researchers Kane Brides and Lloyd Park. "They do that," Park says, unfazed.

Ocean heating can alter currents, bringing relatively fast and sudden weather changes over a vast area. Warmer waters also hold fewer nutrients for marine life. Plus, some scientists think that climbing water temperatures make for faster fish. "The warmer they are, the faster they can swim," the theory goes, according to Morten Frederiksen, a Danish scientist from Aarhus University in Denmark who works regularly with Petersen. "And some birds won't be able to keep up."

Back on Flatey, Petersen wades across another wet meadow, estimating numbers of Arctic terns. "Counting birds is tricky," he says. Some are pacing overhead. Others watch vigilantly from fenceposts. Still others lounge on rocks by the water below.

"That's what they do when they don't have any parenting duties to take care of," Petersen explains of the basking birds. The behavior is normal for August, when the chicks are grown. But not on this day in the middle of July.

No one knows exactly how many Arctic terns there are, but Iceland is believed to hold nearly a third of the world's population, perhaps 500,000 pairs. This year, Petersen and colleagues are conducting a census of Iceland's terns for the first time in a decade. Their findings will be part of the first-ever circumpolar Arctic tern status review being coordinated by the Arctic Council's biodiversity working group, Conservation of Arctic Flora and Fauna.

Dire reports are already coming in from elsewhere. Petersen's longtime colleague, Sverrir Thorstensen, gets a phone call from a friend counting terns in Iceland's largest colony, Hrisey Island. Ten years ago, there were 15,000 pairs in this colony off the north coast.

With a grim face, Thorstensen relays the news of the latest count: "Very simple answer. All the chicks are dead."

The retired biology teacher from Akureyri is the number two bird-bander in Iceland. He's banded 62,000 birds in the past 35 years. When he visited the colony himself earlier in the season, things looked good: lots of nests, lots of eggs.

"All dead," he repeats now, in a low voice. "There are hundreds lying dead."

View Images Black-legged kittiwakes nest in Iceland's sea cliffs, but the number of nests has decreased by more than half over the past 15 years. Photograph by Cyril Ruoso, Minden/Corbis

Toxic Brew

Our high-carbon lifestyle is turning up the oceans' thermostat, and seabirds are feeling the heat. Some will escape by heading north—scientists say a redistribution is already under way. But there's a cap on how far north they can go. More and more species will be trying to cram into a confined space. Sea cliffs and burrow-grounds are limited, and building nests in the open leaves them vulnerable to predators, which also are moving north.

At the same time, civilization's toxic stew is swirling its way north, where it may also contribute to the seabirds' decline. Levels of mercury, which can damage nervous systems and interfere with reproduction, are rising in marine wildlife throughout the North Atlantic.

For other chemicals, the scenario varies by location and foraging behavior. For example, while the banned pesticide DDT has declined in most areas, it remains high in glaucous gulls in Arctic Norway. Brominated flame retardants are ubiquitous, and the perfluorinated coatings called PFCs are holding steady or even increasing in northern Canada's kittiwakes, fulmars, and murres. In Iceland, levels of the legacy pollutants PCBs and other contaminants are so high in murre eggs that authorities recently warned people not to eat them.

Ten years ago, there were 15,000 pairs in this colony off the north coast.

It's difficult to tell precisely where the birds are encountering these chemicals, said Canadian researcher Provencher, who has conducted exposure studies in Arctic Canada. It's also hard to tease out what the health effects are.

While pollution is a definite concern, ecotoxicologists say levels of most contaminants they're finding in northern seabirds don't appear high enough to jeopardize health on their own. But mixed together, they can make a nasty cocktail, adding to the stress caused by food shortage and habitat change. "The combination of all these factors together could wear down the birds," Provencher said.

One important standout, however, is mercury, a poisonous metal spewed by coal-burning power plants. Mercury levels have grown so high in Arctic terns and many other seabirds that they are "definitely in the range where reproduction could start to be affected," Provencher said.

Yet for all the perils they face, there are still millions of seabirds in the north, Petersen says, watching the birds circling Flatey Island and paddling on the bay.