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In October, the first Tufted Puffin carcasses washed up on a chilly beach on St. Paul Island, a lonely Bering Sea outpost between Russia and Alaska. At first, local residents didn’t think much of the dead birds; they were used to finding seabirds battered by violent weather near the island. But as the days passed, puffins continued to arrive. Within weeks, hundreds more had drifted onto the island's beaches, apparently dead from starvation.

The dead Tufted Puffins add another mass mortality event to a string of recent seabird die-offs along the Pacific coast. Last year, around 8,000 Common Murres washed up in in Alaskan history. A year before that, thousands of Cassin’s Auklets on beaches from California to British Columbia.

In a region that has seen back-to-back years of , yet another case of seabird mortality is unsettling scientists. The emaciated seabird carcasses could point to ongoing changes in ocean ecosystems in response to climate change, they say.

“What I keep coming back to is that we didn’t used to see this,” says Julia Parrish, a professor in the School of Aquatic and Fishery Sciences at the University of Washington. She heads the Coastal Observation and Seabird Survey Team (COASST), a network of citizen scientists that have counted seabird carcasses washed up along Alaska’s beaches for eleven years. “We might see mass mortality events every six to eight years,” Parrish says. “Now sometimes it’s twice in one year. In all of the years that COASST has been collecting beach bird data, we have never seen so many mass mortality events so quickly as we have in the last three years.”

Since they found the first emaciated puffin carcasses in October, members of the Aleut community of St. Paul Island have braved high winds and extreme weather to collect nearly 300 of the dead seabirds. However, the data collected on stormswept and isolated beaches on St. Paul likely underestimate how many puffins have died.

“Part of the problem of the Bering Sea is there aren't many people out there to see if the birds are dying or where they’re washing up,” says Kathy Kuletz, a wildlife biologist for the U.S. Fish and Wildlife Service in Alaska. “Often a very generous estimate is that you’re seeing 10 percent of the die-off in an area.”

“Three hundred is not a big number in and of itself,” Parrish says, noting that total mortality could be much higher. “We don’t know the shape or the size of it. It’s very frustrating.”

Tufted Puffins, handsome birds with bright orange bills, distinctive white faces, and golden head plumes, remain abundant along the Alaskan coastline, though their numbers along the west coast of the lower 48 have . They feed by diving deep into the Bering Sea for fatty forage fish like baby walleye pollock. As winter approaches, the birds usually drift farther south. They spend most of their time offshore and are notoriously difficult to track.

The sudden appearance of hundreds of Tufted Puffins far north of their normal feeding areas has so far puzzled researchers. The birds may have wandered north in search of food after coming up empty in their normal hunting areas in the south. The Pacific Ocean has now experienced several years of high ocean temperatures, which may be redistributing fishy prey the seabirds rely on. Pollock populations in the Bering Sea have been fairly steady, but much less is known about the fattier forage fish that Tufted Puffins need to store extra fat and survive stormy winters.

There are other possibilities for the die-off. Warmer waters encourage the growth of algae blooms, which sometimes produce biotoxins. Traces of biotoxins could have disoriented birds and prevented them from hunting. So far scientists haven’t found any signs that the birds are sick; carcasses are still being sent to the U.S. Geological Survey National Wildlife Health Center to be tested for toxins or diseases.

“It’s a process of elimination to identify the mechanism causing the seabirds to starve,” says Robert Kaler, a wildlife biologist at the Alaska branch of U.S. Fish and Wildlife Service. He suspects there are likely several factors involved in the die-offs. So far, no one has found a smoking gun.

As biologists try to figure out why the Tufted Puffins are starving, they’re also unsure why the birds are coming inland near an island that the seafaring species wouldn't normally approach. In the entire decade before this October, only six of the birds had washed up dead on St. Paul Island. And then this year, for still unknown reasons, hundreds and likely thousands of Tufted Puffins altered their usual behaviors to congregate near a stormy island in the Bering Sea and die. It’s possible that a series of intense storms that struck near St. Paul Island in October and November may have thrown the already weakened or disoriented birds off course.

“This seems to be an emerging pattern where birds that appear to be in sort of distressed situations come closer to shore,” Parrish says, noting that the same thing had happened with Common Murres in the Gulf of Alaska last year. “And I have no idea why.”

With these mass starvations among seabirds becoming a yearly occurrence, scientists continue to look into their underlying causes to better predict what the future holds for the important wildlife habitats and lucrative fisheries of the Bering Sea. For Parrish, who has headed responses to each of the recent seabird die-offs, the starvations show a fundamental change in the ecosystem that will affect millions of seabirds, mammals, and fish in the years to come.

“There’s a lot going on,” she says. “And it does not look very good.”