Lessons from the Osprey Garden

From the Spring 2017 issue of Living Bird magazine. Subscribe now.

Much of biologist-naturalist Paul Spitzer’s life has moved in time with the seasonal rhythms of one bird, the Osprey, and one place—the “Osprey garden.”

In late spring he paddles his canoe into the Great Island saltmarsh, 500 acres of prime Osprey habitat where the Connecticut River flows into Long Is­land Sound. In this marshy inlet, Spitzer checks for action in nests among 35 Os­prey platforms that have been erected here since the late 1950s. As he disem­barks, the resident Ospreys take to anx­ious flight. He raises a pole topped with a mirror over a platform nest. These days, he sees abundant breeding success in the mirror’s reflection—three healthy young birds with ragged crests and brown-spangled wings. But it wasn’t al­ways this way.

Spitzer first stepped onto Great Is­land nearly 60 years ago, as an 11-year-old boy in 1957. That year, he accompa­nied birding legend Roger Tory Peterson on a Christmas Bird Count. Thus began a mentorship that set Spitzer onto a ca­reer path to becoming a ecologist.

When Spitzer graduated from college, Peterson urged him to take up the question of what was causing a sudden and drastic decline among the Ospreys.

“At that time, the curtain was rising on the great DDT drama,” says Spitzer.

From the 1960s through the 1970s, Spitzer watched Ospreys almost dis­appear from Connecticut, and he pioneered experiments that helped establish DDT as a cause of their decline. He has also seen Ospreys make a triumphant recovery in the Connecticut River estuary. And with more than 300 ac­tive nests recorded in the state today, he is now turning his attention below the water, where the next challenge for Osprey is a vanishing fish.

The Discovery of the Perils of DDT on Osprey Populations

Peterson tracked the decline of local Ospreys from 150 in the 1950s to just 13 in 1965. He and his wife Barbara tried to help the Ospreys by building dozens of nest platforms to protect their nests from predators such as raccoons. But the birds still weren’t bringing forth fledglings. Food didn’t seem to be a problem—there was no shortage of menhaden, the large-head­ed bait fish that is one of the Osprey’s primary food sources in Long Island Sound. Spitzer had spent hours watch­ing the fish hawks rising from the water with menhaden nearly a foot long in their oversized talons.

“Roger began to suspect DDT,” Spitzer says. In the 1940s and 50s, DDT was used to control mosquito popu­lations in residential areas, especially along coasts and near wetlands. “He had a hunch the Ospreys were ingesting the DDT from fish. Rachel Carson’s findings were informing our discouraging field studies, and I was cutting my teeth as an ecologist studying this new paradigm of environmental toxicology.”

During nest checks, Spitzer found thin-shelled, collapsing eggs and was re­minded of a British study that showed similar thinning in Peregrine Falcon eggs.

Shortly after receiving his biology de­gree from Wesleyan University, Spitzer had the idea to isolate local ecological effects in Connecticut by switching eggs in Osprey nests there with eggs from a healthy population of breeding Osprey near Chesapeake Bay.

“Not nearly as much DDT was ap­plied to Maryland saltmarshes, and it was probably diluted in the far larger Chesapeake system,” says Spitzer. By performing the switch, he could isolate whether the problem was with local en­vironmental conditions or intrinsic to the Connecticut eggs.

The Patuxent Wildlife Research Cen­ter in Maryland signed on to Spitzer’s idea and provided staff to collect eggs.

From the outset, Spitzer saw the Maryland eggs hatch healthy chicks in Connecticut, but not vice versa.

“The embryos in Connecticut eggs died, and we found the shells to be thin by simple measurement,” he says. “We also found dented or collapsed eggs in some Connecticut nests.” None of these problems affected the Maryland eggs.

Next, he arranged transfers of young nestlings from Maryland to Connecti­cut, to look beyond egg problems. The results were the same: “Virtually all the Maryland nestlings fledged in Con­necticut, [so there were] no problems with food at this time. The failure was egg viability,” Spitzer says. Later lab tests revealed DDE (a breakdown product of DDT) as well as PCBs and another or­ganochloride, dieldrin, at much higher concentrations in the Connecticut eggs compared to the Maryland eggs.

“All signs pointed to Roger’s hunch being right, that it was DDT,” he says.

DDT was banned in Connecticut in 1972, and two years later Osprey num­bers on Great Island bottomed out, with just a single nest remaining as the vestiges of DDT made their way out of the ecosystem.

Today, there are approximately 100 active nests at Great Island and the overflow is helping populations at near­by Gardiners Island and eastern Long Island grow. Statewide, the Connecticut Audubon Society’s Osprey Nation mon­itoring project recorded 337 active nests in 2016, and 490 fledged young through­out the state—a rate nearly double that which Spitzer had calculated was neces­sary for a stable Osprey population.

Numbers like these, along with steady positive trends along Breeding Bird Sur­vey routes, help explain why breeding Ospreys are now abundant and wide­spread in Connecticut and throughout the eastern United States. Spitzer points to a combination of factors including an increase in artificial nest sites, a decrease in harmful residues in their food sources, and continued high levels of food avail­ability, particularly Atlantic menhaden.

Osprey and Menhaden

For the last three summers the Connecticut Audubon Society has sponsored Spitzer’s ongoing work in the Connecticut River estuary, but the aim of the research has now shifted to monitoring the relationship between Osprey and menhaden. As in the 1960s, Spitzer’s attention is again focused on Great Island, now fittingly protected as a Roger Tory Pe­terson Wildlife Area. During June and July, Spitzer has documented that the Ospreys’ diet is 95 percent to 100 per­cent menhaden. Spitzer says the story is much the same from Connecticut to Virginia, with menhaden-fueled Osprey nesting colonies experiencing a revival.

“Over 50 years of Osprey study, we have moved from the sad story of DDT-induced egg failure and a declining population to the happy story of abun­dant Ospreys,” Spitzer says. “Our ongoing legacy from Osprey study must be the management of the East Coast ecosys­tem for abundant menhaden. We have to leave enough menhaden in the water to perform their precious and essential eco­nomic and ecological functions.”

Rich in oils and fat, menhaden live in Atlantic coastal waters ranging from Nova Scotia to northern Florida, but reach peak abundance in and around the Chesapeake Bay. In addition to serving as the primary food source for breeding Ospreys and their chicks along the New England coast, menhaden are also a main food source for striped bass and bluefish. And, they constitute a significant fishery for people—second only to pollock among the ranks of fish harvested by volume in the United States. But people don’t eat menhaden for dinner. They process it into other forms, mostly pills.

Most of the nearly 200,000-metric-ton annual menhaden catch is rendered into omega-3 fatty acid fish oil for the health supplement in­dustry. And most of that catch comes via purse-seine fishing, in which two fishing boats circle around a single school of fish and en­close it within a gigantic net. These operations are extremely efficient at catch­ing huge volumes of fish. Only one state (Virginia) currently allows purse-seine fishing of menhaden, but the fish caught in the Chesapeake Bay and Virginia wa­ters account for 85 percent of the total menhaden harvest.

Because a large share of the range-wide menhaden population is clustered in the mid-Atlantic region, harvests there have a significant effect on the population as a whole. As the fish-oil market boomed in the 1990s and 2000s, menhaden populations began to dwindle. In 2010 stocks hit a 54- year low. In 2013 the Atlantic States Marine Fisheries Com­mission reduced the quota of commercial menhaden harvest by 20 percent. Spitzer attributes the recent robust East Coast Osprey populations to the renewed health of the menhaden fishery following these new rules.

“It was a huge win,” says Spitzer.

But now, many ocean conservation­ists say menhaden are once again com­ing under intense fishing pressure. In 2015 and 2016, the quota was increased by about 10 percent, and the menhaden quota for 2017 has been increased by about 6 percent from 2016. Some indus­try representatives are suggesting that the menhaden quota could be raised by up to 30 percent without harming the overall fishery.

Spitzer thinks the ASMFC should be more conservative in what it allows so that the menhaden population doesn’t crash again, as it did earlier this decade. He also thinks the continued abundance of menhaden is critical to the continued abundance of Ospreys.

“It is a great blessing to have been able to study Ospreys for 50 years and counting. I have observed so many pos­itive outcomes for these birds over the years,” Spitzer says. “Decisions about menhaden now will affect not only fish, but birds, coastal ecosystems and, in the end, every one of us.”