WASHINGTON –

At the Maine Coastal Islands National Wildlife Refuge, the tiny bodies of Arctic tern chicks have piled up. Over the past few years, biologists have counted thousands that starved to death because the herring their parents feed them have vanished.

Puffins are also having trouble feeding their chicks, which weigh less than previous broods. When the parents leave the chicks to fend for themselves, the young birds are failing to find food, and hundreds are washing up dead on the Atlantic coast.

What is happening to migratory seabirds? Biologists are worried about a twofold problem. Commercial fishing is reducing their food source, and climate change is causing fish to seek colder waters, according to a new bulletin released by the U.S. Fish and Wildlife Service.

"We've seen a 40 percent decline of Arctic terns in the last 10 years," said Linda Welch, a Fish and Wildlife Service biologist at the refuge. Arctic tern pairs in Maine fell from 4,224 pairs in 2008 to 2,467 pairs last year, the Fish and Wildlife Service said.

Biologists at the Maine refuge are not sure whether herring sought colder waters elsewhere or went deeper, but they are no longer on the surface where the terns pluck them. While other birds can dive deep for food, Arctic terns cannot. "They're not getting herring, so they bring butterfish that the chicks can't swallow," Welch said. "So they starve to death. You have thousands and thousands of chicks dying. It's very sad."

On Machias Seal Island, a shortage of fish prompted 3,000 pairs to abandon their nests in 2007. "They haven't raised any chicks since," Welch said.

Arctic terns arrive at the Maine islands after a month of flying from the Antarctic, about 750 km a day — 22,000 km in total — low on energy, longing for a bite. If they lack food and energy, "they can't keep the gulls off them," Welch said. Gulls eat tern eggs and babies.

In the past couple of years, Welch said biologists at the refuge went to the most productive foraging grounds where seabirds, whales and dolphin prey on herring and spotted fishing trawlers.

"When (the trawlers) come out, the whales and birds disappear, and you don't see them again," Welch said. "I think it's hard to deny that they don't have an effect on these birds."

Migratory birds "are among the most vulnerable groups of species to climate change," said Doug Inkley, a senior scientist for the National Wildlife Federation who studies them. "Migratory birds need suitable areas to breed when they're migrating and on their wintering grounds. Through climate change, if you affect any of these habitats, you've broken a link in the chain. That puts the species in peril."

Climate change also threatens a shorebird, the red knot. As temperatures warm, they are leaving the southern tip of Brazil later for a 15,000-km journey back to their Arctic breeding ground. Timing is key, because red knots might miss the peak of Delaware's horseshoe crab spawn, where they gorge themselves on eggs and double their weight.

"From backyard wildlife watchers to hunters in their duck blinds, unless we take action now, Americans across the country are going to be asking, 'What happened to all the birds?' "Alan Wentz, a retired chief conservation officer of Ducks Unlimited, said in an NWF report, "Shifting Skies: Migratory Birds in a Warming World."

Past events foreshadow the fate of red knots that fail to eat enough horseshoe crab eggs before the long trip north. For years in the 1990s, horseshoe crabs were overfished as bait for shellfish.

As the horseshoe crab went, so went the red knot. By 2000, a population of about 100,000 had fallen to about 44,000, a stunning decrease, said Gregory Breese, a supervisory fish and wildlife biologist for the Delaware Bay Estuary Project office.

For the Arctic tern, the future is just as cloudy in an era of climate change. Fish and other sea life that crave colder water have been swimming to the Earth's poles, abandoning areas such as the warming Gulf of Maine.

In research published in the journal Nature, University of British Columbia scientists found that 968 species of fish and invertebrates they studied fled from the warming waters of their original habitats.

It is not known how puffins get to Maine; living out at sea for most of the year makes them hard to study. But, like terns, they dine on herring. And when they cannot find herring, they bring their chicks the larger butterfish.

Numbers of puffin pairs have increased slightly in recent years, Welch said, but their chicks are smaller and weigh less than before. "What will happen in five years when they come back" mature and ready to mate, she said.

If they make it back at all. "We know the puffin go out to sea, but we really don't know where they go. We don't know the migratory behavior of puffin," Welch said. "But in January through April this year, hundreds of birds washed up dead from Maine to Florida. The birds they found, many of them had starved to death."

It was a rare event. Few birds ever wash ashore; usually they sink at sea. "We think last year was a particularly bad year. Maybe this year will be better."