The birds aren’t finding the fish they need, and so they’re moving on to other areas. They still come back to their nests occasionally, but they’re moving.”

Alan Poole

We’re uniquely positioned to connect these dots. Ospreys are kind of an ambassador and they’ve become an indicator of the overall health of the watershed.”

Meghan Jeans

Just three years ago, Westport’s osprey population was booming. Successful fledges were up, nests were full and observers from Mass Audubon were excited that a corner had finally been reached after a long, long road.

"The population has rebounded so well that they have spread out," Gina Purtell of the Audubon’s Southcoast Osprey Project told the conservation commission in February of that year. "They are restored to their original numbers, their pre-colonial numbers I suspect."

But things have changed since then. And when members of the Westport River Watershed Alliance gather Saturday to celebrate the environmental organization’s 50th birthday with a gala at Quansett Farm in Dartmouth, they’ll have a mystery to solve: What’s become of the birds?

“We know that they have had a poor outcome this year (and) it wasn’t great last year either,” Purtell said Monday.

New leader

There are theories but so far few concrete answers to what’s caused the decline in osprey health seen in Westport waters over the last few years. As scientists look for them, the alliance will head the search.

The WRWA board recently agreed to take over the Audubon Society’s osprey project and will take on the task of tracking the birds from here on in. They’ll be led by Purtell, who will be hired on by the alliance to oversee the work.

“We’re excited,” the alliance’s new executive director, Meghan Jeans, said. “We’re uniquely positioned to connect these dots. Ospreys are kind of an ambassador and they’ve become an indicator of the overall health of the watershed. It’s a really interesting opportunity to answer some key questions.”

Just a blip? Or more?

In the late 19th and early 20th century, there were up to 1,000 breeding pairs of osprey counted along the coast of southern New England to New York. But by the early 1960s, their numbers had declined precipitously due in large part to the pesticide DDT, which causes weak, thin eggshells. At their nadir in 1964, six breeding pairs were counted in Westport and Dartmouth.

But things began to change in 1965, when Gil and Jo Fernandez started raising nesting poles on their land adjacent to Allens Pond. The birds flocked to them and, coupled with the banning of DDT seven years later, the population began to rebound by as much as 10 percent per year.

Purtell, Jeans and osprey expert Alan Poole, who has worked with the osprey project for years, all agree that the numbers have come down since the good news was reported in early 2023.

“We have been monitoring this population long enough to be able to discern this blip,” Purtell said.

According to Poole, observations this year mimic similar trends that have been noticed in other populations from the Chesapeake Bay north to southern New England.

There are currently just shy of 100 nests in the east and west branches and in the Audubon Society’s Allens Pond, and observations this year found 50 to 60 percent of them had at least one adult osprey.

Meanwhile, he said, osprey “have had very poor reproductive success and four out of five young birds counted this year starved — in a good year it’s one out of five; in a bad year, two.”

“It’s not only that nests are being abandoned in ways that we haven’t seen before,” he said. “The birds aren’t finding the fish they need, and so they’re moving on to other areas. They still come back to their nests occasionally, but they’re moving.”

There are plenty of theories, including the decline of menhaden stocks as far south as the Chesapeake. These protein-rich fish have long been a staple in ospreys’ diets. And while state officials said this week that local menhaden populations are not in crisis, the birds just aren’t getting them or other food as they once did.

“The fish are not accessible (and) we don’t know why. There’s great hatch success (but) the problem was that the chicks are starving. We found very underweight chicks and absent adults. So it’s anecdotal, but what we observed correlates with fish being unaccessible — it’s not that they’re not there. We just don’t know why they’re not getting fish.”

Emily Stolarski of Mass Fish and Wildlife said this week that overall across the Commonwealth, state scientists have “not found evidence that osprey numbers are in decline from a lack of food (but) there are some areas this year where low nesting success has been reported, including South Shore and Westport.”

There is no hypothesis yet on why, she said, but “our biologists will be discussing possible causes with monitoring partners” like the alliance.

Purtell, Jeans and Mike Sullivan of the alliance board said they are looking forward to finding answers.

“We’re excited,” Sullivan said. “To hire Gina is very exciting for us and it dovetails very much” with the alliance’s mission.

“Now we get to explore the reasons behind it, or the factors, open up partnerships, get community members involved,” Purtell said.