The odd-looking seabirds — with their rounded heads, golden head plumes and distinctive bright orange bills — typically migrate south to warmer waters that late in the year, so having any puffins wash ashore was rare enough. But the arrival of hundreds of emaciated puffin carcasses, as well as of a second species known as the Crested auklet, alarmed and astonished local residents and scientists.

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“Part of the mystery is what in the heck were those guys doing there? Why hadn’t they left? … That means there’s something going on in the system that’s not too good,” said Julia Parrish, a professor at the University of Washington who also runs a large citizen-science project known as the Coastal Observation and Seabird Survey Team, or COASST. “We know month in and month out what is normal, what to expect.”

The mass die-off of the widely beloved birds off coastal Alaska — one of a growing number of “mass mortality events” affecting seabirds recently — was anything but normal.

Parrish and a group of colleagues used weather data to estimate that between 3,150 and 8,500 birds probably died, most likely from starvation. In a paper published Wednesday in the journal PLOS One, the authors theorize the die-off is at least partially attributable to the changing climate.

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“This mortality event represents one of multiple seabird mortality events that have occurred in the Northeast Pacific from 2014 to 2018, cumulatively suggestive of broad-scale ecosystem change,” they write. Such episodes, they add, “are indicators of a changing world, and particularly of climate warming.”

Tufted puffins breed in the Bering Sea off the Alaskan coast, feeding on various fish and marine invertebrates, which themselves rely on plankton for food. But several years of significant warming and reduction in sea ice has resulted in troubling changes, such as the migration of certain “forage fish” such as capelin, juvenile pollock and other energy-rich prey that puffins and other birds depend on to survive.

The authors suggest the climate-fueled shifts that probably affected the food supply, as well as the birds being in molt — a process that replaces their feathers but also hinders their ability to fly — ultimately doomed the puffins that washed ashore on St. Paul Island.

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“They didn’t get where they were going,” Parrish said. “They ran out of gas. They ran out of time.”

Similar circumstances appear to have fueled an unprecedented die-off of common murres — a thin-billed sea bird — between 2015 and into early 2016 off Alaska and other parts of the U.S. Pacific Coast. The following year, another seabird die-off happened in the Bering and Chukchi seas of Alaska and Russia, affecting northern fulmars, short-tailed shearwaters and other species.

In fact, 2018 marked the third year in a row that scientists documented “massive” seabird die-offs in the Bering Sea region, according to the National Park Service. It was the fifth consecutive season of mass mortality events in the North Pacific, the fourth consecutive year of these die-offs in Alaska, Parrish said.

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“Seabirds are good indicators of ocean ecosystem health. Recent mortality events are concerning in that they may be pointing to significant changes in marine ecosystems,” the agency wrote in an update late last year.

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As recently as this month, dead and dying common murres have been reported along the Mendocino County coastline in California, though the cause of that die-off remains undetermined.

“We are now just bracing for what is going to wash in next,” Divine said. “It’s kind of terrifying.”

Such episodes have also unfolded elsewhere in the world in recent years.

In the Gulf of Maine, puffins have been found dying of starvation and losing body weight — although scientists there have helped aid breeding in an effort to boost populations. Across the Atlantic, puffin populations also have been in decline, partly because of human factors such as hunting, but also, scientists say, because of changes to food supplies.

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Wednesday’s study also comes on the heels of a United Nations report earlier this month that found roughly 1 million plant and animal species are on the verge of extinction, with alarming implications for human survival. That report by seven lead co-authors from universities around the world goes further than previous studies by directly linking the loss of species to human activity. It also detailed how those losses are undermining food and water security, as well as human health.

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Parrish acknowledged many questions remain about precisely what led to the puffin die-off in 2016, as well as others documented before and since.

“People often think you can point to climate change the way you can point to a person with a gun who had just shot somebody,” she said.

The reality, she said, isn’t so simple when it comes to figuring out all the forces shaping a complex ecosystem such as the Bering Sea. But she said each die-off offers clues that significant changes are underway and that more troubling patterns might lie ahead.