Fish Scarcity Affects Osprey Population On Cape

The resurgence of ospreys after the U.S. Environmental Protection Agency banned the use of the synthetic insecticide DDT in 1972 has long been seen as an environmental advocacy success story. 

But now another threat is looming and the call is out to increase osprey nest monitoring efforts on Cape Cod.

In response, the Harwich Conservation Trust (HCT) is planning to increase staff and volunteer efforts to track the progress of nesting ospreys in the spring, work that will be coordinated by HCT's TerraCorps service member Sam Ogburn.

Back in the 1950s and 60s, DDT caused catastrophic thinning of eggshells for ospreys and other raptors, causing populations to crash. But the present day threat doesn't involve insecticides. It's about fish. While the cause has yet to be determined, a critical source of osprey food was in short supply this year during a key time: after the birth of osprey chicks.

When ospreys return to Cape Cod, usually around the end of March, the impending herring run offers a rich supply of food. But the run subsides by early June, around the time that osprey eggs hatch. Then it's time for ospreys to turn to other fish to feed their young.

Menhaden, a small oily fish in the herring family, usually arrive in Cape waters in time to help fill the gap. But this year, their numbers appear to have dwindled, particularly in the Buzzards Bay area.

"I think multiple food sources failed for Cape ospreys from Falmouth into the Mid-Cape," said Mark Faherty, science coordinator at the Mass Audubon Wellfleet Bay Wildlife Sanctuary. "It wasn't just menhaden, but I think the most important factor was that menhaden didn't show up in Buzzards Bay in June. And that's when ospreys need them."

It wasn't just a dearth of menhaden. "Other fish were absent, too," said Faherty. "I think particularly summer flounder, maybe scup, maybe sea bass weren't inshore where ospreys could get at them. I don't know why. I heard from everybody that the fishing was terrible, for people and ospreys, along the south side of the Cape."

According to Faherty, the effects of this fish scarcity were most devastating for ospreys that nested in Falmouth. "The Falmouth population had really bad productivity," he said. Because of a lack of food, "a lot of chicks died in the nest, and they produced a fraction of the normal number of chicks that they would typically produce."

A typical nesting season in Falmouth might produce as many as 200 osprey chicks, said Faherty. But this year, the number was down to about 70. 

However, other osprey populations in the state did pretty well, according to Faherty. "This was not like the Massachusetts osprey population failed," he said.

Faherty pointed out that osprey populations have been quite robust on the Cape for a long time, but the recent development deserves attention. "I'm not worried until it becomes a trend, but as a scientist, I want to know what happened," he said.

His concern is heightened by reports of similar osprey decline in Virginia. In 2025, the College of William and Mary's Center for Conservation Biology completed an aerial osprey survey along the seaside of the Virginia portion of the Delmarva Peninsula. 

According to their findings, "compared to historic accounts and benchmark surveys conducted during the 1970s and 1980s, the 2025 survey reveals a nearly complete collapse of the population." 

The study also reports that "the underlying causes of this population decline are unclear," but adds that "the most likely cause of the decline is prey availability."

In a letter to a Congressional committee, the United States Geological Survey corroborated the findings of the William and Mary study, adding that "data collected there indicate the principal contributing factor to poor breeding performance was loss of young due to starvation. This was likely caused by limited prey capture and/or prey delivery to nests."

In Virginia, some are looking at menhaden fishing practices as a possible contributor to osprey decline. 

According to a statement about the osprey population collapse from the Chesapeake Bay Foundation, a nonprofit conservation organization, "Virginia is the only state along the Atlantic coast that still allows industrial menhaden reduction fishing in its state waters. That sole remaining reduction fishing operation, Reedville-based Omega Protein, harvests well over 100 million pounds of menhaden from the Commonwealth’s waters each year."

This summer, Virginia lawmakers approved funding for research on the menhaden population in Chesapeake Bay and whether catch limits should be established.

Faherty cautions that it's too early to draw conclusions about possible causes of the Cape osprey situation and that more information is needed. 

In recent years, with the osprey population seemingly secure, most Mass Audubon osprey monitoring efforts on the Cape have focused on working with Eversource to solve issues caused by ospreys nesting atop utility poles, which can cause bird electrocution and power outages.

When the ospreys return next spring, Faherty plans to re-focus monitoring efforts on what's going on in their nests. HCT will help support these efforts.

It's good to remember the community spirit and sense of accomplishment that accompanied the return of ospreys after the DDT ban. Many environmentally-minded Cape Codders pitched in to help establish osprey nesting platforms to welcome back these beautiful raptors, including an HCT-led effort that established six platforms in Harwich.

Now, it’s time for HCT volunteer citizen scientists to jump back into action to help these awesome ospreys. For decades, they have been welcome harbingers of spring and winged proof of the power of environmental stewardship. We want to do all we can to keep it that way.