Each spring, roughly 90% of the entire endangered Northwest Atlantic population of Roseate Terns migrates to three New England islands to breed after spending the winter on the coast of Brazil. Two of these islands, Bird Island and Ram Island, sit right off the coast of Southeast Massachusetts in Buzzard’s Bay.
Unfortunately, the species is in steep decline, and scientists don’t know exactly why. Just 4,000 documented pairs of breeding Roseate Terns remain in the Northwest Atlantic—fewer than half the number that existed less than a century ago.
Although Roseate Tern breeding sites are protected and well managed in Massachusetts, there is little known about what happens to them after they leave the state.
Mass Audubon’s Bird Conservation Program actively works with partner organizations in Brazil, where nearly the entire population of Northwest Atlantic Roseate Terns spends its non-breeding months. Tagging adult birds and tracking their GPS activity begins to unlock the mysteries behind the Roseate Tern’s decline and guides conservation efforts to help the species rebound before it’s too late.
About Roseate Terns
The Roseate Tern, a seabird found around the world, earns its name from the faint rosy tint on its breast. While Common Terns—its close relatives—are more frequently seen along Massachusetts's shores, Roseate Terns also dive into the coastal waters of the Commonwealth during the summer. While the two are strikingly similar in both behavior and appearance, the Roseate Tern can be distinguished by its black beak, in contrast to the Common Tern’s mostly red beak. This elegant bird has been featured on Mass Audubon’s logo for decades.
Terns produce just one chick per breeding pair each year, so each adult death takes a long-term toll on the population, ramping up the need to understand and ultimately reduce threats to the species.
Identifying Mortality Risks
Since 2017, Mass Audubon and partners, including Centro de Estudos e Monitoramento Ambiental (CEMAM), have worked together to identify the highest known source of mortality to the Roseate Tern: collisions with human-made structures, such as powerlines and land-based wind turbines, during its winters along the coast of Brazil.
This international partnership led Mass Audubon’s team to Galinhos, Brazil, in 2017 after partners recorded a staggering number of adult terns fatally colliding with powerlines on the beaches of this coastal city. During the trip, the team documented more than 100 adult Roseate Tern fatalities through powerline collisions—the largest known mortality source for adult Roseate Terns in the entire hemisphere. With collaboration from the local energy company, visible markers were placed at the site in Galinhos, which reduced collisions by 80% over the next five years.
Rafael Revorêdo of CEMAM (third from the right) guiding the international team through the plan to capture Roseate Terns on the beaches of Galinhos, Brazil.
Leveraging GPS Technology
Although powerline collisions in Galinhos decreased, mortality sources continue to grow along the coast of northern Brazil as the Roseate Tern population struggles to rebound. More information about the challenges Roseates face was needed.
Staff from Mass Audubon, National Audubon Society, American Museum of Natural History, and CEMAM partnered to tag 15 Roseate Terns with GPS devices in Galinhos in February 2024. The lightweight yet powerful technology weighs just 2.5 grams, allowing the birds to maneuver freely while providing vital information about their migratory pathways. Transmitters across Brazil and the United States detect GPS activity as Roseate Terns travel past, creating a more accurate migratory map. Not only does tracking their movements help identify current areas of mortality, it helps identify where to prevent new potentially lethal interferences, including a proposed offshore wind development off the coast of Brazil. A proactive strategy will help ensure long-term success of Roseate Tern populations by stopping mortality at the source.
What’s Next
So far in 2025, the team has tagged another 15 Roseate Terns in Brazil to broaden the dataset. In the coming years, Brazilian partners will continue to tag Roseate Terns in their wintering grounds to help paint a more robust picture of their entire lifecycle. The team has successfully tracked several Roseate Terns traveling from Brazil back to the coast of Massachusetts during their first GPS-tracked migration.
At the same time, Mass Audubon is developing plans to incorporate Roseate Tern conservation throughout their entire annual lifecycle by supporting conservation efforts during their time here in Massachusetts, continuing to mitigate known threats during the winter, and working with our partners to understand the viability of this endangered population.
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