Flocking once again to the harbor and bay

Ospreys: Although the birds' numbers are rising, some researchers worry that urban habitat remains a threat to their survival.

July 21, 2000|By Joel McCord | Joel McCord,SUN STAFF

On top of a red marker in Old Road Bay, a few hundred yards from the dirty browns and oranges of Bethlehem Steel's Sparrows Point plant, a fledgling osprey is taking the first, tentative steps toward leaving the nest.

There's another on a piling in the Patapsco River above Key Bridge, just off the dock where freighters unload aluminum ore for Alcoa, and more on pilings and navigational markers among the rusted hulks of Curtis Creek near W. R. Grace chemicals and the Hess oil terminal. The birds, once gone from the Patapsco and nearly gone from the Chesapeake Bay, have returned in astonishing numbers.

Yet scientists aren't so sure that Baltimore Harbor, one of the bay's toxic hot spots, is such a great place for creatures that feed exclusively on fish.

"We have a situation where birds are laying eggs that don't hatch or those that do hatch are being fed toxic food and don't grow well," said Barnett A. Rattner, an environmental toxicologist for the U.S. Geological Survey.

Ospreys are "high on the food chain," he says, and the contaminants in sediments "tend to magnify as you go up."

Rattner and Peter C. McGowan, an environmental contaminants biologist with the U.S. Fish and Wildlife Service, have been checking on nests in the Patapsco, Anacostia and South rivers since March, analyzing eggs for polychlorinated biphenyls (PCBs) and testing blood and feather samples for heavy metals and other contaminants.

The Patapsco and Anacostia are two of three "Regions of Concern" in the bay watershed - the third is the Elizabeth River in Virginia. The scientists use the South River, south of Annapolis, for comparison's sake.

The last such study was done 15 years ago, and there is "very little information after that," says McGowan. Three days a week, McGowan and Rattner shove off in a small, open boat to check on 15 nests in each river, down one shore and up the other. They've clambered up pilings and across navigational markers to get an egg or samples from a hatchling while parents have circled menacingly overhead. Neither has felt the beak or the talons of an angry mother.

Rattner concedes that it may seem "cruel" to take one of three or four eggs from a nest for study, but he says, "Nature's cruel."

Some eggs are attacked by predators, and females kick others out of their nests if they think something is wrong with them.

The dark brown birds, known as fish hawks because of their dietary habits, mate for life. They can be found from Maine to South Carolina and along the Gulf of Mexico. Osprey hover over the water, searching for prey, then dive feet first, their talons spread, to grab menhaden, sunfish, herrings and silversides to take back to the nest.

In the winter, they migrate to South America and return to the same nests in spring to lay two to four eggs. The largest population is in the Chesapeake Bay.

"In fact, the bay is known as the Osprey Garden of the World," says Rattner.

It wasn't always so. Osprey populations declined sharply in the 1950s and 1960s as the use of pesticides such as dichlorodiphenyltrichloroethane (DDT) spread. The birds disappeared entirely from the Patapsco because of the double whammy of pesticides and other chemicals that fouled the water and the fish that swam in it. The Chesapeake osprey population was down to 700 pairs.

Since the banning of DDT and other harmful chemicals in the 1970s, the birds have rebounded. Two thousand pairs are in the bay, a third of the East Coast population, and the population is growing in the Patapsco.

One recent day, McGowan, Rattner and Julie Thompson, a Fish and Wildlife Service biologist, motored through the littered muck of the Patapsco's Middle Branch to get to the first nest near Curtis Creek. It seemed empty from the water, but Rattner held a mirror on a long, telescoping pole over the nest to spot a tiny bird hunkered low, waiting for food. Only one of the three eggs had hatched. At other nests, fledglings, cheeping, ke-uking and trying to spread their wings, watched the boat as it circled. The closer to the mouth of the river, the more young birds filled the nests.

The fledgling at Sparrows Point stood on the edge of the nest, staring at the boat. At last, the bird spread its wings, flapped once, twice, a third time, and lifted off clumsily over the superstructure of the navigational marker, then down in a wobbly path toward the water before catching the wind and soaring.

A few minutes later, it returned, caught a wing on the corner of the marker, crashed into the nest and regained his balance.

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