Lauren Divine first heard that the birds were dying on October 13, 2016, when one of her colleagues stumbled across the corpse of a tufted puffin while walking along a beach on Alaska’s St. Paul Island. The next day: another carcass. Soon, several of the island’s 450 residents started calling in with details of more stranded puffins. Some were already dead. Others were well on their way—emaciated, sick, and unable to fly.
Nestled in the middle of the Bering Sea between Alaska and Russia, St. Paul is the largest of the four Pribilof Islands, which together support more than 2 million seabirds. Dead individuals aren’t uncommon. Divine’s team, which works on environmental issues that affect St. Paul’s Aleut community, would usually expect to find one or two on its monthly beach surveys. But that October, “you couldn’t walk more than a few steps before having to pick up another bird,” she says. “It was pretty apparent that something was really wrong in the environment.”
The team stepped up its surveys, braving biting winds and crashing waves to comb the beaches on all-terrain vehicles. Over the next few months, it located more than 350 bodies, a rate that was about 70 times higher than normal. Stranger still, most of these birds were tufted puffins—a species that very rarely washes up dead. In the previous decade, the team had only ever found six puffin carcasses, and never in the winter months. It seemed that the puffins had become the latest species to experience a mass-mortality event—a large-scale die-off, of a kind that’s becoming more and more common.
To work out how many puffins had actually died, Timothy Jones of the University of Washington used the locations of the known bodies and data on local wind patterns to simulate where the dead birds were coming from. He estimated that between 3,150 and 8,800 tufted puffins perished in the final months of 2016.
What killed these birds? Most of them were intact, with no signs of either predator attacks or disease. Some of them had saxitoxin—a potent poison made by algae—in their stomach, but at levels almost 100 times lower than what would be considered safe for humans to eat. Instead, the most likely cause of death was starvation. The birds were extremely thin, with weak flight muscles and very little body fat. “They literally didn’t have enough to eat and became weak to the point of death,” says Julia Parrish of the University of Washington, who led the study.
Tufted puffins look like fancier versions of the more widely known Atlantic puffins, with elaborate yellow eyebrows that sweep backwards down their neck. On land, they have a clownish, goofy disposition. But in the sea, they become grace personified, using their streamlined body and sickle-shaped wings to fly underwater in pursuit of small fish.
But what if there are no fish to pursue?
The climate of the Bering Sea is changing rapidly. In recent years, the sea ice that would have extended southward in the winter has become unprecedentedly thin and sparse. And that has affected everything from tiny plankton to titanic walruses.
The ice sheets create a layer of super-cold water called the “cold pool,” which sits at the bottom of the Bering Sea. Pollock, cod, and other fish like to congregate in large numbers at the edges of this pool, providing excellent hunting grounds for puffins and other sea birds. When the cold pool doesn’t form, as has been in the case in recent years, the fish spread out over larger distances, and are harder to catch.
And when they are caught, they’re worth less. In the warmer waters, the plankton have shifted toward smaller and less energy-rich species, and the fish that eat those plankton have become similarly thinner in calories. Fish-eating birds, such as puffins, “are going from Clif Bars to rice cakes,” Parrish says. “They have to work much harder to get the same energy content. And this is happening over thousands of square kilometers of ocean, so it’s not like they can say, ‘Oh, there’s no Clif Bars here, so I’ll go to the next grocery store.’”
These changes hit the birds at the worst possible time—when they change their coat of feathers. Puffins use their body feathers as a wetsuit that keeps water away from their skin and helps them retain heat. To keep that suit secure, they regularly replace all their old plumes in a dramatic synchronous molt. Over the next few weeks, they need a lot of energy to grow new feathers, but they can barely fly or dive. For that reason, they typically molt from August to October, when food ought to be plentiful. If it isn’t, the birds don’t make it.
It’s no coincidence that most of the tufted puffins that washed up during St. Paul’s mass-mortality event were in the middle of molting. At a time when they were most in need of food, and least able to get it, the dwindling sea ice forced them to travel farther afield for sparse, energy-poor scraps. “In short, climate change causes seabird starvation,” says Melanie Smith, the conservation director for Audubon Alaska. “It’s not the only factor at play, but it is the common thread among similar events.”
Other species in the Bering Sea are suffering, too. Ever since 2013, when the massive marine heatwave known as “the blob” formed off Alaska, “we’ve seen a whole bunch of mass-mortality events,” says Parrish, who documented a similar die-off of Cassin’s auklets in 2015. “In every case, there are thousands to hundreds of thousands of marine birds that should normally be way offshore, but are crowding into pretty narrow strips of coastal land. They can’t keep it together, they’re starving to death, and they’re washing in.”
“Bird die-offs have happened up there before,” says Phyllis Stabeno, an oceanographer at the National Oceanic and Atmospheric Administration. “But it’s unusual for there to be so many of them, spread out over the whole [Bering Sea] system.”
“It’s an ecosystem that, in my experience, is screaming constantly at us to pay attention,” Parrish adds.
Kathy Kuletz from the U.S. Fish and Wildlife Service adds that most mass-mortality events probably go unrecorded, because they happen out at sea, and the carcasses never make it to shore. “Our office has conducted about 15,000 to 20,000 kilometers of seabird surveys annually since 2007, and before 2014, we averaged 1 to 2 dead bird encounters per year at sea,” Kuletz says. “Since then, we've had between 20 and 70 dead birds per year. Those numbers may not seem like much, but bird carcasses are difficult to see from large vessels moving at 10 to 14 knots, so this could represent a much larger problem than is documented by monitoring efforts on land.”
These changes are also affecting the people who live on St. Paul and the other Pribilof Islands. The native Aleut, or Unangan, people have long traditions of hunting puffins and collecting their eggs. The birds aren’t that important as a food source now, but they’re still culturally significant. “People enjoy having them around,” Divine says. “When the community saw the die-off, it was alarming and upsetting. They wanted to know what is happening to the species, and what management measures the federal government will take to understand and fix this situation.”
Other seabird populations are declining, too, Divine says. Several species roost on cliff faces, and without sea ice to buffer the coast from fierce winter storms, those cliffs are eroding at an alarming rate. The shorelines are wearing away, too, destroying the breeding sites where endangered Steller sea lions would normally congregate. “Their numbers here have gone to almost zero,” Divine says. “These huge biological and physical changes are very noticeable in the Pribilofs. We’re in the middle of it all.”
And yet, the exact scope of those changes is hard to assess, because the Pribilofs are so remote, and because censuses of seabirds rarely attract significant funding. Only through the efforts of Divine’s team of volunteers did the extent of the puffin die-off become clear. “Everything up here is data limited,” says Austin Ahmasuk of Kawerak, a consortium of Alaska Native tribes. “We only know about [the puffins] thanks to this citizen effort.”
“This is a sad bird story, but it’s also one about how community science and mainstream science can work together,” Parrish adds. “Listening to local expertise and incorporating that into what we do … that’s the only way science is going to save the world.”