An expanded survey of ospreys nesting around the Chesapeake Bay this year is finding that they are failing to produce enough chicks to sustain their numbers, with fewer eggs being laid and many hatchlings dying in the nest or simply disappearing.
“We will absolutely see a broad population decline if the pattern continues,” said Bryan Watts, director of the Center for Conservation Biology at the College of William and Mary, who has been coordinating the survey.
The preliminary results from the survey, which began in April and runs through the end of July, add urgency to questions about the reason or reasons for ospreys’ current reproductive woes. Along with bald eagles and brown pelicans, ospreys have rebounded from near extinction caused by reproductive failures linked to the widely used pesticide DDT, which was banned in 1972.
This time, Watts contends, based on studies he’s done in Virginia’s Mobjack Bay and with the Baywide surveys in 2024 and 2025, that ospreys nesting by the saltier waters of the Bay are suffering from “food stress” because there aren’t enough of their dietary mainstay —Atlantic menhaden.
His findings have reinforced long-standing calls from conservationists and recreational fishing enthusiasts to shut down large-scale commercial harvests of menhaden in the Bay. They contend that a Reedville, VA-based fishing fleet working for Omega Protein, which processes the menhaden into fish oil and pet food, is depleting the Bay’s stock of menhaden. They argue that it is reducing the food supply not just for ospreys but also for Atlantic striped bass, a popular and economically valuable fish that spawns primarily in the Chesapeake’s tributaries.
Spurred in part by reports of osprey reproductive problems, East Coast fishery managers are set to discuss whether to enact a range of precautionary menhaden harvest curbs when they meet in early August.
Scientists with Watts’ center, the U.S. Geological Survey (USGS) and several other organizations have been monitoring osprey nesting activity this year in 20 locations on both shores of the estuary, up from 12 areas tracked in 2024.
Female ospreys usually lay two to four eggs, and the young will spend about 55 days in the nest being fed fish by their parents before fledging.
For example, Watts said, this year’s survey spotted ospreys nesting in 34 spots along Virginia’s Elizabeth River. Those pairs produced 39 chicks by mid-May, but within a few weeks, he said, 20 of the hatchlings died or disappeared from their nests before they could fly.
Osprey nests, often built on navigational markers or platforms placed over water, fail for a variety of reasons. Storms might blow the nests off, while bald eagles, owls and other predators could poach eggs or chicks. Diseases may take a toll. Chemical contamination is no longer the threat it was, though traces of DDT and other banned pesticides still linger in some fish in the Bay’s rivers.
Watts said rain and hot weather the past two years could be a factor in the birds’ difficulties, but the “driver,” he maintains, is “food stress.” A lack of sufficient prey leads ospreys to lay fewer eggs or even abandon nests, he said, and hatchlings can starve to death if their parents can’t provide enough sustenance.
Testing the theory
Based on years of study, Watts and colleagues with the Center for Conservation Biology reported seeing a steep decline in osprey reproduction in Virginia’s Mobjack Bay. They linked the problem — even worse than in the DDT era — to a shortage of food, particularly Atlantic menhaden, a dietary staple for ospreys in that part of the Bay.
The Baywide nest surveys are testing that hypothesis regionally. Ospreys feed on a variety of fish, depending on where they nest in the Bay watershed. In addition to menhaden, they prey on juvenile striped bass, Atlantic croaker, gizzard shad and catfish. Surveyors have installed cameras at some nest sites to track the types and number of fish provided to the chicks, but data are still being gathered and analyzed.
In 2024, Watts enlisted the USGS and others to survey osprey nesting activity in a dozen locations around the Bay, to see if reproduction elsewhere was similarly affected. Ospreys in six high-salinity areas, where Watts says the birds tend to feed mostly on menhaden, experienced major reproductive shortfalls, producing fewer than 0.6 young per nesting pair. The other four brackish-water sites had moderate or mild shortfalls but still averaged fewer than one chick per nest.
By comparison, ospreys nesting over freshwater in the upper James and Rappahannock rivers with different fish diets produced 1.36 young per pair, above the minimum needed to sustain their number. The breakeven threshold is 1.15 young per pair.
Barnett Rattner, a USGS scientist who is participating in the surveys, said, “Things are seemingly worse than they were last year” in Maryland’s Harris Creek and around Tilghman Island. In 2024, the USGS team found eggs in only 47 nests of about 90 nesting sites there. This year, Rattner said, there were less than half as many active nests in the same area.
Looking further north
As part of the expanded survey this year, the USGS also is monitoring ospreys along the Chester River farther north. They have monitored more than 100 active nests built over waters that have a range of salinities and approach freshwater at upriver sites, Rattner said. As of late June, while some nests had failed, the number of eggs and chicks are “in that normal range,” he said.
“But there’s another month to go,” he noted in late June. “It’s a critical period for a lot of the nests because many of them have young at different stages. This is going to be the acid test period where they have to be fed. We’ll see if they all make it.”
Another area added to this year’s survey is Maryland’s Severn River, which joins the Bay at Annapolis. Watts said he had expected ospreys there to do relatively well. Ken Green, head of Operation Osprey, a small nonprofit that monitors osprey nesting on the river, said spring looked promising, with 63 active nests spotted by mid-May.
“We had lots of eggs,” he said. “We were very excited.”
But the bottom dropped out over the following month. Many of the nests that appeared to be occupied in April were later abandoned. And those where the females had laid eggs likewise dwindled. By late June, there were only 15 chicks left in nine nests, he said.
“It’s quite alarming what we were seeing,” Green said, adding he was baffled by the decline.
Paul Spitzer, a veteran ornithologist who volunteers as Green’s scientific advisor, said it was unusual in his experience to see so many osprey pairs nest but not lay eggs or lay them late in spring. The young that hatch from those late-laid eggs, he suggested, likely have a hard time surviving the brutal summer heat, which peaked this year in late June.
“The simplest hypothesis [for the nest failures] is food limitation upon ospreys’ spring return from the tropics,” Spitzer wrote in an email. There aren’t enough menhaden for them to feed on, he said, and no alternative fish that offer the same nutritional value.
Widespread problems
After the 2024 survey, Watts said he thought ospreys’ nesting woes were limited to the Bay’s mainstem and that birds nesting up the rivers, in fresher water that might offer other fish than menhaden, would produce enough chicks to offset the poor performance along the Bay’s shore.
But based on preliminary results from this year’s survey, Watts said he no longer believes that. The poor reproduction documented along the Bay’s mainstem and in many of its lower tributaries has been so severe this spring and summer, Watts said, that it more than offsets generally successful breeding observed among ospreys nesting on the upper Bay and its rivers. Unless something changes, he said, the Bay’s osprey population appears destined to decline.
“Does this mean that osprey are going to disappear from the Chesapeake? Absolutely not,” Watts wrote in an email. “Does it mean that some people will lose ‘their’ resident pair of osprey that they enjoy? Yes. We are already seeing this …”
With late-summer heat and storms still possible in the final weeks of the nesting season, Watts said, “It can only go down from here.”
The situation is even worse on the Atlantic side of the lower Delmarva peninsula. Watts’s center reported this summer that an aerial survey of osprey nests there had found a near complete collapse of the population. Though he suspected a lack of prey again, he noted there have not been any studies of those birds’ diets.
Menhaden data gaps
Watts’ assertion that a lack of menhaden is impacting the Bay’s osprey reproduction is disputed by Omega Protein and its supporters. They point to a 2022 stock assessment for the Atlantic States Marine Fisheries Commission, which found that the coastwide population of menhaden is not being overharvested.
Conservationists contend that Omega’s large-scale purse seine harvesting in the Bay is causing a localized depletion of the fish in the estuary, even if the coastwide menhaden population is otherwise healthy. To date, there has been no research to test that claim. Virginia lawmakers called for such a study in 2023 but have declined to fund it for the past two years.
Three fisheries scientists with the Virginia Institute of Marine Science also have challenged Watts’ linkage of osprey nest failures to menhaden shortages. They don’t dispute that ospreys are struggling to reproduce, but they say the data Watts relied on “do not establish a clear relationship with menhaden abundance and availability.” Watts acknowledges that more Baywide information is needed, but he maintains that the Mobjack Bay study clearly identified a link between menhaden availability and osprey nesting success there.
The Atlantic States fisheries commission is scheduled Aug. 7 to discuss a report that it commissioned on “precautionary management” measures it might take to ease fishing pressure on Chesapeake menhaden. Among the possible actions: imposing harvest closures in spring when ospreys are nesting or reducing the overall Bay harvest cap, now set at 51,000 metric tons.
Commission members, though, have been split over whether there’s a need for any changes. Some have urged waiting for a pending scientific update on the menhaden population and an assessment of how many need to be left in the water to serve as food for other species.
Watts acknowledges there could be more than one cause for ospreys’ troubles around the Bay.
“To me it is a combination of food stress and the weather,” he wrote in an email. “The weather has not been the best and that is layered on top of the ongoing food stress. When the broods are not well fed, they are more vulnerable to both storms and heat waves. We have lost a lot of young ospreys in the mainstem of the Bay over the past month.”
While ospreys up the rivers are faring better, it appears they’re not producing enough chicks to make up for the losses. So while the birds are unlikely to disappear from the Chesapeake, he cautioned that they may well be less abundant and visible in future.
“Whatever you believe about the [cause],” he concluded, “the ospreys are speaking loudly that conditions are not as they need to be.”