As the Arctic Warms, Hungry Polar Bears Are Eating More Seabirds—Wiping Out Colonies

One summer day in 2024, a polar bear walked across the flat, wild shore of Spy Island, Alaska. Common Eiders nested there, with birds and eggs in the hundreds. By the end of the day, almost all of them were gone.

“When we arrived, it was very quiet,” says Kayla Shively, conservation ecologist at the Wildlife Conservation Society, which has been tracking the colony for years. “No adult females remained on the island. We started noticing scat, crushed eggshells, and bear tracks zigzagging from nest to nest.” Shively’s team had stumbled upon a rising threat to Arctic seabirds: hungry polar bears. 

As the Arctic warms, polar bears are losing the summer sea ice where they hunt seals, their primary prey. That’s driving them onto land, where they increasingly forage for seabird eggs, nestlings, and sometimes adults. While the behavior is not new, researchers are observing it more often in the Canadian Arctic, Svalbard, and Greenland in recent decades. 

A new scientific paper, published in Polar Research this month, provides the first report of large-scale bear-bird predation in Alaska, confirming that it’s happening across the Arctic. 

On Alaska’s north coast, the shore is mostly low tundra fronted by barrier islands in the Beaufort Sea. These islands are critical nesting grounds for seabirds, beyond the reach of traditional predators like Arctic foxes. Historically, polar bears rarely appeared here in summer, but as sea ice has melted, their numbers have increased sixfold in the past 20 years. Nests are particularly vulnerable to predation on these small islands, where one or two polar bears can devastate an entire colony.

The paper reports on two colonies: Cooper Island’s Black Guillemots and Spy Island’s Common Eiders. 

Small and gravelly, Cooper Island is the long-time summer home of Mandt’s Black Guillemots, an Arctic subspecies. These birds originally nested under planks, ammo boxes, and other debris left by the U.S. Navy following the Korean War. When ornithologist George Divoky, co-author of the study, began observing the colony in 1975, polar bear predation was rare. But in the breeding seasons from 2008 through 2010, bears killed nearly half of all nestlings. In 2011, researchers put bear-proof nest cases on the island, but eventually, bears learned to break them open, even submerging them in water to flush out adult birds. In 2024 and 2025, bears caused complete reproductive failure in the colony. 

Farther east, on Spy Island, Pacific Common Eiders, also a subspecies, nest in driftwood, sparse vegetation, and low dune ridges. Females of this largest sea duck in the Northern Hemisphere spend the greatest proportion of time on their nests of any waterfowl, Shively says. Here, too, reports of bear predation had been rare since surveys began in the 1970s. Then, in 2016 and 2017, bears destroyed 11 percent of more than 200 monitored nests. And that day in July 2024, a single bear destroyed 89 percent of nests in less than 24 hours. 

For these two species as a whole, the polar bear threat isn’t existential. Indeed, “most seabird species in the Arctic are still in relatively good shape,” says Don Lyons, director of conservation science at Audubon’s Seabird Institute. “They’re not at risk of extinction in the next 50 years. But the’'re going to face real challenges, and could become endangered in that time frame.” 

Like predation from polar bears, many of those challenges are driven by the climate crisis. Sea ice loss is contributing to increased storm surges, flooding, and shoreline erosion, shrinking nesting grounds for eiders. “In northern Alaska, that’s the greatest threat to Pacific Common Eiders,” says Shively. For the guillemots, warmer waters mean fewer Arctic cod, their primary food. 

Compared to those threats, polar bears may be only a short-term problem, but for an unfortunate reason, says Andrew Derocher, a biologist at the University of Alberta. Elsewhere in the Arctic, bears are less vulnerable to sea ice decline, and are learning to hunt species like reindeer and walrus. But in the southern Beaufort Sea, he says, “the population is hanging on by a claw. In 50 years, I don’t think we'll have polar bears here.”

In the meantime, polar bears won’t switch to a wholly bird-based diet, since it doesn’t provide enough calories. An adult polar bear needs about 54 Common Eider eggs to meet its daily energy requirement. That day, the bear ate about 255 eggs—equivalent to a yearling ringed seal, and enough food for less than five days. 

And while some birds are threatened by polar bears, others partly rely on them for food: When polar bears kill seals, a variety of birds feast on the leftovers, including Ivory Gulls, Rough-legged Hawks, and Snowy Owls. “There’s a whole trophic cascade that comes from taking sea ice out of an ecosystem,” Derocher says. That system is fragile, and deeply interconnected.

Arctic sea ice decline is among the most significant climate-driven habitat losses on the planet, reshaping ecosystems and dangerously rewriting predator-prey dynamics. Faced with these threats, “we can’t lose sight of the big picture,” Lyons says: Taking climate action at a global scale. Each year, sea ice loss is directly proportional to human-caused fossil fuel emissions. For bears and birds alike, the future is uncertain. The cause of that uncertainty, and its solutions, are not.