‘Unprecedented’ Mass Death of Seabirds in Western U.S. Baffles Experts

At first scientists weren’t too surprised by the carcasses washing ashore. When young auklets fledge in late summer, they all enter the water at the same time and start competing for food—shrimp-like krill and tiny crustaceans called copepods. For various reasons, last summer’s birth class of Cassin’s auklets was gigantic. Researchers expected a higher death toll, too.

But they now are perplexed by the sheer numbers of dead birds and the spreading geographic extent of the die-off.

“Death at this level and over this much real estate has to be from more than just that,” Parrish said.

By comparison, not one of the five largest U.S. bird mortality events tracked by USGS since 1980 is estimated to have topped 11,000 deaths. In Europe, according to the U.K.-based Royal Society for the Protection of Birds, the worst die-off on record occurred in 1983, when 57,000 guillemots, razorbills, puffins, and other seabirds perished in the North Sea and washed up on the British coast.

“You get some of this with seabirds every year,” said David Nuzum, with the Oregon Department of Fish and Wildlife. “You get so many juveniles out there, and they’ve got this steep learning curve for feeding after being separated from their parents, so you always get a die-off in winter. But I’ve never seen anything like this, ever, and I’ve been here since 1985.”
Cassin’s auklets like this one, swimming near the Santa Cruz Municipal Wharf in November, number between 1 million and 3.5 million along the West Coast of North America.

PHOTOGRAPH BY PETER LATOURRETTE

On some beaches the Cassin’s auklet death toll was a hundred times greater than any bird die-off ever tallied there, and six times worse per kilometer than the body count recorded after the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska. On a single stretch of beach on Christmas Eve in Oregon, U.S. Fish and Wildlife Service biologist Mike Szumski collected 250 carcasses—and left nearly as many behind.

“You’d find them piled up in clusters on the wrack line, where the tide leaves sea grasses and debris,” Szumski said. “Most were in these states of decay, but every now and then we’d see tracks coming out of the water and find a bird that was just barely clinging to life. They were just skin and bones.”

The gruesome auklet deaths come just as scientists around the globe are seeing a significant uptick in mass-mortality events in the marine world, from sea urchins to fish and birds. Although there doesn’t appear to be a link to the virus that killed tens of millions of sea stars along the same shores from California to Alaska over the past 18 months, some scientists suspect a factor in both cases may be uncharacteristically warm waters.

The U.S. Geological Survey and others have performed animal autopsies, called necropsies, on several of the emaciated Cassin’s auklets. They’ve found no evidence of disease or trauma—no viruses or bacteria, no feathers coated with spilled oil. The birds appear simply to have starved to death.

“There’s very little evidence of food in their GI [gastrointestinal] tracts or stomachs,” said Anne Ballmann, with USGS’s National Wildlife Health Center.