Scientists Can Now Track the Roseate Tern’s Migration—and Identify Dangers Along the Way

The sun is just starting to set off the tip of Galinhos, a peninsula in northeast Brazil, and Rafael Revorêdo is holding a beer koozie as he sits in a folding chair with legs that have sunk deep into the sand. Unlike most people visiting this tropical paradise on a warm February evening, he’s not here to relax. As a biologist at Centro de Estudos e Monitoramento Ambiental (CEMAM), a local conservation NGO, he’s here to study Roseate Terns, migratory seabirds named for the delicate pink hue their breast and belly feathers take on during breeding season. 

The koozie is an improvisation on a Pringles can—an improvisation itself—that Revorêdo and his colleagues will use to hold each tern they catch while they weigh it. (The local market was out of the chips.) He’s lining the container with parchment paper to make sure the birds’ long, thin bills don’t get stuck in its Styrofoam interior. While every unbanded Roseate Tern they catch will receive a unique ID bracelet, the researchers are especially interested in capturing up to 15 individuals heavy enough to also sport GPS tags. Once affixed to the terns, these trackers will gather data the researchers hope will help protect Roseates and other seabirds while allowing renewable energy development to advance.

The elegant and imperiled seabirds have long found a haven in Galinhos, but offshore wind development poses a growing risk. With its strong, consistent gales, the Galinhos coast is considered “the filet mignon of wind” in Brazil, says Revorêdo. Onshore wind farms are already well established in the region and contribute significantly to Brazil’s renewable energy goals. Now there’s growing interest in offshore wind farms. There are at least 12 proposed projects that if built could create a wall of turbines that presents a potentially deadly obstacle for Roseates.

Every evening from November through early April, Roseate Terns return from long days of foraging at sea to roost on the beaches in Galinhos. Most of the birds are members of the northeast population, which was hit hard a century ago, first by the millinery trade and then by development and rampant predation by gulls and other animals on their breeding grounds. Today those sites are heavily managed, but the population still isn’t recovering. “It seems clear that there are other threats holding them back,” says Don Lyons, director of conservation science at Audubon’s Seabird Institute. “We need information on where Roseates are when they’re not at their breeding colonies.” 

By tracking the birds, Lyons, Revorêdo, and their colleagues are hoping to get a more detailed picture of the paths the birds take—and where intervention might be warranted. 

A Path to Safety

On this tagging trip in February 2025, the researchers will work until the wee hours, four nights in a row, trying to catch Roseate Terns as they return to land. As the sky darkens, the researchers begin playing Roseate calls from speakers set up behind mist nets that catch the birds as they return to land. The first evening they catch four Roseate Terns in quick succession, two of which already have bands. Keenan Yakola, an Oregon State University Ph.D. student, looks up the first, which he discovers is from Maine, the place he also calls home. He immediately knows the second bird is from Great Gull Island, a major breeding colony site off Long Island, because of the number sequence on its band. 

The team starts with the tern from Maine. Working in the soft red glow emanating from their headlamps, Yakola calls out its measurements, and Lyons jots them down. At 113 grams, the bird is hefty enough to sport a GPS tag. The tern lets out a few squawks as Yakola passes it to Revorêdo. “It’s okay, sweetheart,” Revorêdo whispers to the bird. “Gentle, gentle.”

Yakola slips the tag’s straps, made of Stretch Magic, usually used for making necklaces, around the tern’s legs. He then adjusts the tag so its weight is well distributed across the bird’s lower back, its antenna pointed tailward. The gadgets record location, altitude, speed, and other data every 15 minutes; the team collects the trove of information via radio receivers as the birds fly by them at their breeding and nonbreeding grounds. This is the first of 15 birds that will receive a GPS tag this season—the same number they tagged the previous year. (They’d tag more if they could, but at $700 per unit, 15 is what’s in the budget.) 

When he finishes, Yakola carefully takes the bird from Revorêdo and turns it upright. “I’ll see you in Maine,” he says, as he releases it into the air with a toss, his palms facing the sky as the bird opens its wings and takes flight.

The tags deployed over the past two years have revealed that the birds in Galinhos tend to make straight flights between their beach roosts and shelf breaks about 30 miles offshore, where fish are known to congregate in the upwelling of cold, nutrient-rich water—information that could influence the siting of new turbines to avoid tern highways. Over that same period, radio receivers the researchers deployed at breeding colonies in the northeastern United States captured, for the first time ever, the exact migration routes of seven Roseates. In November the team celebrated another first: tracking the southern trips of three terns, including one tagged in Galinhos last February. The data indicate that terns could overlap with offshore wind development and power lines at various points throughout their migration.

As offshore wind expands here and across the birds’ range, the scientists hope their findings will help officials mitigate potential harm. Interventions might include painting turbine blades to increase visibility, adjusting turbine height, and siting wind projects to avoid tern highways.

A Balance of Power

Even though the terns’ nesting colonies along the U.S. East Coast are protected, the birds experience challenges throughout the year. Climate-driven changes take a toll during the breeding season: More powerful storms flood and erode nesting sites, and marine heat waves alter the distribution of fish that terns subsist on, causing young birds to starve. 

What’s more, the renewable energy needed to help stem global warming can pose risks to the birds. Collisions with wind-energy transmission lines were once the leading energy-related threat to the small seabird in Galinhos. In 2014, soon after the first wind farms were constructed there, volunteer wildlife monitors with CEMAM began noticing a distressing trend: Dead and injured Roseate Terns were turning up near the area’s newly installed power lines.

In 2017 alone, they found 110 Roseate bodies. Several of the dead or injured birds had been banded as chicks on Great Gull, Ram, and Bird islands, the main tern breeding grounds off the East Coast of the United States. The monitors at CEMAM reached out to Helen Hays, an American ornithologist known for her seminal work restoring Common and Roseate Tern populations, particularly on Great Gull Island. Hays, in turn, relayed the news to ornithologist Joan Walsh, who had also worked on Great Gull.

“I can do everything right on Great Gull Island and make you an extra 500 baby Roseate Terns, but what good is that if, when they fly to Brazil, they encounter a thousand offshore wind turbines?” says Walsh. “We need to understand what that threat landscape is across their entire range to do good conservation.”

Walsh worked with the scientists at CEMAM, including Revorêdo, to better understand what would be required to reduce or avoid mortality. One of their experiments included using markers from a Colorado-based company called Power Line Sentry, which they spaced along distribution lines. The markers had two kinds of stripes that enabled terns to see the wires: one that reflects sunlight during the day and another that absorbs it and then glows at night. The markers were installed in December 2021, and subsequent monitoring found that the intervention dramatically reduced the number of deaths.

“We work tirelessly all year to try to keep that species moving forward on its recovery track,” says Walsh. “When you discover the largest anthropogenic kill that’s reversible, you do something.”

That’s why the researchers at Galinhos spend all night tagging birds. By mapping Roseate Tern movements, they hope their findings will help officials mitigate potential harm as offshore wind expands off the Brazilian coast and throughout the birds’ range. As difficult and time-consuming as it is to monitor avian mortality on land, it’s even harder at sea, where carcasses quickly disappear. Interventions to prevent injury and death might include painting turbine blades to increase visibility, adjusting turbine height, and creating structure-free corridors in key areas to provide safe passage. “We need renewable energy,” says Yakola. “But it can be done in a way that benefits both people and wildlife.”

This story originally ran in the Winter 2025 issue as “Safe Passage.” To receive our print magazine, become a member by making a donation today.