The bodies started washing ashore on St. Paul Island, Alaska, in October 2016. One after another, the small carcasses of seabirds—mostly puffins—landed on the beach in extraordinary numbers.

The people of St. Paul Island, an Aleut community in the Bering Sea, are accustomed to seeing a lot of birds—millions stop there during their annual migrations. But they're not used to seeing them like this. What was happening in October 2016 was the beginning of a mass die-off. Thousands of tufted puffins were dying for no apparent reason, except for maybe one: changes in the ecosystem due to climate change.

"There's no way to avoid that something is going on here," said Julia Parrish, a professor of ocean fishery sciences at the University of Washington and the executive director of the Coastal Observation and Seabird Survey Team (COASST). "The ocean is screaming."

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The puffin die-off, which continued into January 2017, is documented in a study out Wednesday in the scientific journal PLOS ONE. Parrish, one of the authors of the study, said the puffin mass mortality event is one of six such events her team has documented along the Pacific coast since 2014. In one event, 400,000 Cassin's auklets died. A year later, it was more than 500,000 Common murres.

"We've had die-offs before, but now we're seeing them every year," said Parrish. "Altogether that's millions of birds dying. Millions."

In recent years, the Arctic has warmed at twice the rate of the rest of the world and warmer waters have come up through the Bering Strait, wreaking havoc on the ecosystems there. This winter, during a time when the sea ice should have been expanding in the region, an area the size of Montana melted instead.

The puffins are an example of the changes: though they are common around St. Paul Island and elsewhere in Alaska, by the time of the die-off, they should have already migrated out of the area. And yet there they were, dying of starvation in droves.

Dead puffins documented on St. Paul Island in 2016. Credit: Aleut Community of St. Paul Island Ecosystem Conservation

The number of dead birds is high enough that they clearly came from beyond the normal St. Paul Island population. But why they starved—and why they did so around St. Paul Island—remains unclear. The authors posit that climate change-driven shifts in their food supply may have been the driving cause.

The study comes on the heels of a major report from a global scientific panel which found that a million species are at risk of extinction, driven in part by climate change. The magnitude of that loss is hard to imagine, Parrish said—but it's easier to comprehend "when you're knee deep in birds, with more washing ashore."

During the die-off, tribal members pitched in to assess the problem, combing the beaches and collecting carcasses, said Lauren Divine, the director of the Aleut Community of St. Paul Island Ecosystem Conservation Office and one of the study's co-authors. "We were running into so many dead puffins, or sick and alive ones that wouldn't fly away when we would approach," she said.

At that time of year, they should have been out in the north Pacific, Parrish said. All told, more than 350 carcasses were discovered, which the scientists extrapolated out to a mortality event killing between 3,150 and 8,800 birds.

Trouble in the Food Chain

Climate change is well established in the Bering Sea region. Recent years have seen less sea ice there than any time on record. It's freezing up later and melting earlier, and some areas that used to have significant ice in the winter are hardly getting any now. Without the ice to buffer the inhabited islands in the region, storms are bringing massive waves that eat away at the shore and threaten those who live there.

"We're seeing an increase in the transport of ocean heat through the Bering Strait," said Mark Serreze, the executive director of the National Snow and Ice Data Center. This has been a hallmark of recent years. "We're trending toward this no longer being the unusual situation, but closer to a new norm," he said.

The story of what happened to the puffins on St. Paul Island likely begins with that influx of warm water and the changes that are taking place at the bottom of the food chain, Parrish said.

As more warm water flushes north, the pool of intensely cold water that sits on the Bering shelf is shrinking and moving north. "That change in the amount of the cold pool is resetting a lot of the Bering Sea ecosystem on the bottom," she said. The temperature shifts are causing changes from tiny species like zooplankton, the bugs of the ocean, on up to the forage fish that would provide food for puffins.

"There's a shift to smaller and less energy intense species," Parrish said. "It's like going from a Cliff bar to a rice cake. You can eat the same volume, but you're not going to get the same nutrients. If you're a predator, you have to work harder and spend more energy to get energy."

Climate change is also dispersing species as they search for new, more suitable habitats. Parrish said that for the puffins, it was as if their local grocery store no longer carried their favorite foods. Humans can just go to the next grocery store; it's more complicated for a bird.

"That's the larger story of climate change," she said. "It's changing things over such an enormous space that you literally can't fly out of it."

The Human Impact

On St. Paul Island, the puffin deaths were a loss for the community and a sign of the larger climate challenges facing its residents.

About 450 people live on St. Paul Island, roughly 90 percent of whom are members of the Aleut tribe. Subsistence hunting provides a sizeable portion of most peoples' diets there, said Divine. Though puffins are no longer hunted for food, they hold a great deal of cultural significance.

"This island is 450 close-knit people and their culture is at risk," said Divine. "Climate change is not just this thing somewhere off in the future." The changes are already happening to their food system—with fishermen having to travel farther to catch what they need and new species showing up—and to the physical island as cliff faces erode.

"Fortunately, Alaska natives are very resilient. They've been there tens of thousands of years and will be into the future," said Divine. "But they're losing very important pieces of their culture due to things completely out of their control."

In the two years after the puffin die-off, Divine said the island saw major deaths from other bird species, and, anecdotally at least, locals reported seeing fewer puffins than normal. Those numbers now appear to be rebounding, but Divine said they're bracing to see what 2019 brings.

"What's it going to be this year? We're preparing for a summer of looking at our shorelines."