WILMINGTON, Del. (AP) - At the Lewes Little League Park, a pair of osprey showed up recently — among the first of more than 200 nesting pair expected to return to Delaware to mate, lay eggs and produce young between now and September.
This nesting pair is part of a remarkable recovery. Scientists last did comprehensive sampling of osprey in the Delaware estuary and Inland Bays in 2002 and there were barely a couple dozen nests. They revisited that work in 2015 and are just beginning to review the findings.
“The osprey is a sentinel” species, said Barnett Rattner, an ecotoxicologist with the U.S. Geological Survey, who worked on both surveys.
These birds, like bald eagles, herons and egrets, can be great indicators of local pollution problems, he said.
What they found both in Delaware and in a similar study done in the Chesapeake Bay is that osprey populations are thriving and productivity rates exceed what is required to sustain the population, he said.
But the sampling still shows low residual pesticides and legacy pollutants in the birds. His findings in the Chesapeake were similar.
The Chesapeake and its tributaries are a breeding ground for an estimated 10,000 nesting pairs of osprey.
There and in the Delaware estuary and Delaware Inland Bays, the research team found that the birds are surviving despite the continued presence of toxic chemicals that were banned in the 1970s. These chemicals remain in the food chain from the bottom sediments up through the aquatic food chain into the fish the osprey eat.
The Chesapeake work, completed last year, revisited an earlier study done in 2001. The Delaware study repeated work done in 2002.
Because of Delaware’s history of legacy pollutants and industrial pollution, Rattner said he expected to find worse conditions than what they found in the Chesapeake.
“It amazed me,” he said, because the preliminary results from the Delaware Bay show lower or non-detect levels of the chemicals in the eggs.
They were “actually better” than the Chesapeake, he said.
In both studies, researchers tested fish, osprey eggs and the blood plasma of osprey chicks.
In Delaware, ospreys nest along the Christina River, the central area of Delaware Bay and the Inland Bays.
They have a similar range throughout the Chesapeake.
In 2002, Rattner visited osprey nests in Delaware where he collected egg, blood and feather samples to look for signs of environmental toxins such as pesticides and polychlorinated biphenyls.
He looked at egg shell thickness, productivity and the number of fledglings each nest produced.
“In 2002, there was a lot of egg loss,” he said. “In 2015, there was very little egg loss. It was a very stable population.”
Osprey populations declined because of the pesticide DDT. Widely used for mosquito control in Delaware in the 1950s and 1960s, it was linked to egg-shell thinning and nest failure in species like osprey and bald eagles. Both eat fish and typically nest near water. DDT was banned in 1972.
“Like many raptors, DDT did a number on them,” said Kate Fleming, a state wildlife biologist.
The population in Delaware was at 25 nesting pairs in a survey done in 1971, she said. By 2003, the number of nesting pairs had grown to 119 pairs.
In 2014, the number was just under 200 nesting pairs.
Fleming said the state doesn’t do osprey surveys every year. There is a state program where citizens can report nests.
While the nests are found along water throughout the state, the largest concentration of nests is in the Inland Bays because the birds favor the wide open water, she said. Ospreys dive feet first into the water to catch the fish they eat so they prefer shallow areas.
“It’s good news,” Rattner said. “Things are not perfect but they sure are better than they were.”
Information from: The News Journal of Wilmington, Del., https://www.delawareonline.com
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