For over an hour now, Bob Schutsky has been peering through the mist over the wide Susquehanna River. The object he's watching here in Maryland's Conowingo is rare: a male bald eagle, perched motionless on a rock in the middle of the river.
Suddenly catching an updraft, the bird lifts off and soars upward. It circles higher and higher until it turns and screams toward the water, talons outstretched.
A splash and three powerful wingbeats later, the eagle is aloft again, grasping a struggling fish. Mr. Schutsky beams with pleasure.
He is a biologist with the Philadelphia Electric Co., which manages both Conowingo Fisherman's Park and Muddy Run Fisherman's Park, which is 14 miles upstream from Conowingo in Pennsylvania. He is telling a group of bird-watchers that in 1989, for the first time in four decades, a pair of bald eagles built a nest on Lower Bear Island in Muddy Run and hatched two eggs. Now the pair has returned to patch and reweave the same nest to raise a second family.
Mr. Schutsky finds that few sights in nature capture people's imaginations like bald eagles in flight. And he finds that he enjoys the bird-watchers almost as much as the birds themselves.
"People seem to be drawn to birds of prey," he says, "and especially when they're our national symbol." And indeed, on this rainy winter day, penetrating cold doesn't seem to bother the 50 or so people who've come out with binoculars and cameras to wait and watch from an observation deck, which was built on the river bank by the Philadelphia Electric Co.
Both parks on Conowingo Pond, as residents call it, were built and are managed by the Philadelphia Electric Co. as part of a "good neighbor" policy in exchange for the construction of power-generating plants beside the river.
In fact, naturalists think the reason that the eagles have returned to the lower Susquehanna is that the warmth and turbulence of the water passing through the dams keeps the river free of ice -- so the birds can fish all winter.
During especially harsh winters, when parts of the river freeze, bald eagles -- like the black vultures that also live in the parks -- have been known to eat carrion: squirrels, mice, rabbits and other birds. But fish is their primary diet.
The electric company also has turned its attention to the Susquehanna's fish population. It is constructing fish elevators so a native food fish, the American shad, can migrate upstream to its traditional spawning grounds.
At present, park officials trap the shad and truck them past the series of dams that have blocked natural migration since the mid-1800s, when the first dams were built. The fish are released near Harrisburg, Pa., to continue their migration unimpeded.
While the fish are important to the river's wildlife habitat, and keep the eagles fat and happy, it's the eagles that attract visitors to the park.
"I think I see three immature eagles over there on the tower," says a boy, squinting through one of five telescopes Mr. Schutsky has set up on the deck.
"You can tell their ages by the color of their beaks and feathers," Mr. Schutsky says. His penciled list of bird sightings for this day totals 24 species, including tundra swans, mallards, downy woodpeckers, northern flickers, Carolina wrens, rock doves and common mergansers.
Bald eagles aren't the only raptors native to this stretch of river. Regulars report seeing peregrine falcons, ospreys, owls and golden eagles.
Also at Conowingo this day is Joy Howell, a naturalist from Muddy Run Park. She has come for a special program called Eagle Watch.
"The best part of my job is leading field trips for school kids," she says. The weekday trips for inner-city schools from Philadelphia and Baltimore run daily during the week from March 1 through late fall, and introduce students to the variety and complexity of the river's ecosystem.
But the environmental outlook along the lower Susquehanna hasn't always been so upbeat. For many years, local farmers sprayed insect-infested crops with DDT, a pesticide that prevents normal formation of birds' eggs. The poison gradually entered the food chain, preventing the birds from reproducing.
Meanwhile, illegal hunting and the construction of three dams in Conowingo by the electric company damaged irreplaceable lakefront and riverside habitat. By the 1960s, the bald eagle was gone from the lower Susquehanna River.
After 1972, when environmentalists' protests led to the banning of DDT, the eagles began a slow comeback. In 1986 they built two nests in Conowingo, and one in 1990 in Muddy Run. There also are five other nests at Aberdeen Proving Grounds, a U.S. Army weapon-testing facility near the mouth of the Susquehanna on the Chesapeake Bay.
Eagles mate for life and raise one to two fledglings each season; they use the same nest every year. After many years of repairing and rebuilding, the nests grow enormous, sometimes as big as 16 feet thick and 8 feet across.