Tracking Eider Ducks, Searching for Clues

Tracking Eider Ducks, Searching for Clues

On a cloudy morning in late July, the research vessel A.O.K. motors out of the Schiller Coastal Studies Center into Harpswell Sound. On board is Olivia Ho '28, who has been making regular forays into these waters over the summer on an important monitoring mission.

As the boat leaves the dock, Ho activates the telemetry equipment, a ten-foot antenna linked to a receiver. They're searching for eider ducks-in particular, the females that were tagged earlier in the summer.

Back in May, ten eider hens were captured using a humane device called a mistnet and tagged by biologists with Biodiversity Research Institute (BRI), a Portland-based nonprofit that aims to assess the impact of toxic chemicals and contaminants on the marine ecosystem. Blood and feather samples were also taken before the creatures were released unharmed. Ho has been working with researchers at BRI over the summer. Their goal is to see where the eiders have moved to and whether their ducklings, which typically hatch in early June, have survived.

"How it works is that we point this antenna in different directions, and whenever it detects a bird that we've tagged, there's a frequency system that pings our receiver, which starts beeping when it's in the right direction," explains Ho. "This helps keep track of the ducks' movements." Over the course of the morning, the antenna directed the team toward a number of locations in Casco Bay, pinpointing the whereabouts of about half of the tagged birds, none of which appeared to have any surviving broods.

Mortality rates among eider ducklings are typically very high, says Ho, with some 80 to 90 percent of a brood not making it to adulthood, often falling prey to eagles. This summer, that number looks even higher though, she adds, which is causing the hens to move further out to sea. "We're not sure why this is happening, but it does raise questions."

Her summer project is part of ongoing research by BRI. Chemicals and industrial pollutants have been leaking into the Gulf of Maine for a long time, but the issue was brought into sharper focus two years ago following a major spill of "forever" chemicals known as PFAS, often used in fire suppressant foams.

A malfunction in one of the hangars at the former Brunswick Naval Air Station in 2024 caused around 1,500 gallons of the material to leak into the local environment, including rivers, ponds, and the ocean-specifically around Harpswell Sound, where the Schiller Coastal Studies Center is located. This was the largest toxic spill in Maine's history, and the sixth largest in the US.

Not surprisingly, samples taken from the tagged eiders in Harpswell all showed some level of PFAS exposure, with higher levels being found in those caught nearer the site of the spill. Researchers say it's also important to consider that eiders feed close to breeding colonies during the nesting period and that their diets consist of marine animals like mussels, clams, and other types of shellfish and bivalves that live on the ocean floor-all of which makes them a good bellwether for measuring how toxicity travels up the food chain.

After the spill in 2024, BRI wanted to get more detailed information on how eiders use Harpswell Sound, what the potential exposure to PFAS through their prey might be, and how duckling survival compares to other sites nearby. As well as tracking the birds, Ho's role also involved sampling prey, such as mollusks, across the landscape in Harpswell Sound. The data she has gathered will be used by BRI to try to piece together exactly what the effects of contaminants are on the Gulf of Maine ecosystem.

There are no clear answers yet, and researchers say they still have a lot to learn. To this end, BRI is preparing to work with Ducks Unlimited and the state on a two-year aerial survey of Maine's eider duck population. Starting next spring, they will fly the entire coastline, counting the birds as they go.

Chemicals and industrial pollutants have been leaking into the Gulf of Maine for a long time, but the issue was brought into sharper focus two years ago following a major spill of "forever" chemicals known as PFAS, often used in fire suppressant foams.

Anecdotal evidence suggests the eider duck population in Maine has fallen considerably in recent years-a trend potentially exacerbated at least in one area by the 2024 PFAS spill-and scientists expect this study to help determine if PFAS chemicals are indeed a factor in these declines.

As for Olivia Ho, who is about to start her junior year as a chemistry major, she is proud to have played her part using the facilities at Bowdoin's Schiller center. "It's been a fun summer," she says, "although not the most uplifting of topics."

Ho's summer internship was funded by the Office of Career Exploration and Development (CXD).