Avian Flu Threatens Seabird Nesting Colonies on Both Sides of the Atlantic

Highly pathogenic avian influenza has decimated nesting seabirds in Europe and Canada, raising concerns for eastern U.S. populations.

Editor’s note: This story has been updated to reflect new positive test results from terns in Maine, the first confirmed cases of avian flu at seabird colonies on the East Coast of the United States.

Seabird colonies on both sides of the Atlantic have been devastated by avian flu outbreaks in recent weeks. Thousands of Northern Gannets have died at nesting sites in Europe and Canada, their carcasses washing up on the shores of the Maritime Provinces and the British Isles. On St. Kilda, Scotland, avian flu threatens to strain the Great Skua population. In the Netherlands, an entire colony of Sandwich Terns was wiped out. 

And on Wednesday Audubon learned of the first confirmed cases of avian flu at Atlantic seabird colonies in the United States after a string of tern deaths at breeding sites in Maine. The results indicate that the highly pathogenic avian influenza (HPAI) that ravaged wild birds across the country this spring has arrived in New England’s dense seabird colonies. 

This breeding season, researchers at Pond Island and Stratton Island have been finding one to two dead Common Terns every day—with no signs of predation, injury, or starvation. Don Lyons, the conservation science director for Audubon’s Seabird Institute, noted that some death is normal at these colonies. However, certain signs pointed to HPAI: At least two of the victims had been seen compulsively shaking their heads, a symptom of neurological issues associated with avian influenza. Reports of potentially sick birds not flushing when approached are also troubling. “This suggests that HPAI is present at more than one of our islands, and one can logically speculate that it is likely present, or will be soon, at all of our islands with nesting terns,” Lyons wrote in a follow-up email. 

The new test results confirm that the disease is present at at least one of those sites: All four Common Terns from Pond Island sent to a lab tested positive for HPAI, according to Lyons. Common Terns and Arctic Terns from other islands tested negative. 

Scientists have been tracking the current strain of HPAI in North America since December 2021, when the first case was detected in Canada. It remains unclear exactly how the pathogen arrived on the continent, but genetic analysis has shown that the North American strain is descended directly from the European strain

“Based on the experience that the European countries have had, it looks like it's not necessarily going to slow down anytime soon,” says Samantha Gibbs, the lead wildlife veterinarian at the U.S. Fish and Wildlife Service. “They’ve been dealing with it for a couple of years now at least, and it’s not just going away.”

Terns around the world have been among the hardest-hit species in recent outbreaks. More than 1,000 Caspian Terns on Wisconsin’s Lake Michigan coast have died since late May, with testing identifying HPAI as the cause.

In the Netherlands, where the current European strain has been circulating since 2016, the virus’s impact on Sandwich Terns has been catastrophic. Thousands of terns across multiple colonies have been killed this breeding season, with one colony of more than 7,000 birds being completely wiped out earlier this month. Hundreds more have died at the country’s largest nesting colony. A research site in Germany, meanwhile, is documenting an exponential spike in deaths during an ongoing outbreak at the Banter See that has killed hundreds of Common Terns.

So far, there has been no such increase in mortality rates with the Maine Common Terns that Lyons studies. But these reports are still worrying for seabird researchers. “The fact that terns can be so severely impacted has us really concerned,” he says. 

Because Common Terns frequently move around between colonies, Lyons says that an influenza outbreak at one colony would quickly spread to others. An HPAI outbreak in Maine could spell catastrophe for nearby colony-nesting seabirds like Atlantic Puffins, Arctic Terns, and Least Terns. Lyons is particularly worried about Roseate Terns—this species, which is endangered in the Northeast, shares nesting colonies with Common Terns.  

Lyons and his team are also keeping a close eye on Atlantic Puffins, whose historic Maine populations were reestablished in the late 1970s by Steve Kress, the founder of Project Puffin and former executive director of Audubon’s Seabird Restoration Program. “It appears that puffins are susceptible, like pretty much all species—I haven’t heard of anything that is likely resistant,” Lyons says. 

Seabirds’ dense nesting colonies make them particularly vulnerable to fast-spreading diseases like avian flu. “If you drop a virus into a high-density population, transmission risk is amplified,” says Bryan Richards, emerging disease coordinator at the U.S. Geological Survey’s National Wildlife Health Center. 

Lyons hopes that a sort of avian social distancing would lessen the impact of avian flu on the Maine tern colonies. The species most heavily affected elsewhere breed in extremely close quarters, even for seabirds—Sandwich Terns nest, on average, only a foot apart. Common and Roseate Tern nests, on the other hand, average about three feet of separation. But like many things about HPAI, scientists don’t know how this will actually turn out.

“We’re facing kind of an evolving threat, and it just doesn’t seem very predictable at the moment,” Lyons says. 

One worrying unknown is the effect an outbreak might have on a species’ overall population. Terns have relatively long lifespans—the oldest recorded Common Tern was at least 25 years old. This strategy offers advantages during years of bad weather or low food supply, but an influenza outbreak could make its risks evident. “They can't raise a lot of young in a given year, so when adults are dying, we really worry about the population overall,” Lyons says.

Matters are only made worse by the fact that scientists are helpless to treat sick birds. Instead, they say that the best way to support bird populations during avian flu outbreaks is to reduce outside stressors. “We can't really alter disease outcomes to a great extent in wild birds—the virus is going to do what it’s going to do,” Richards says. He thinks the best way to make a difference is by enabling populations to recover. 

While a healthy, resilient population can withstand disturbances from disease, Gibbs adds, a population stressed by factors like habitat loss, decreased food supply, or pollution will have a harder time rebounding. “It’s a whole intricate and complex system, all of which needs our care and attention,” she says.