Conowingo Dam on the Susquehanna River in northern Maryland is a good place to experience wintering water birds, particularly when local impoundments and much of the river freezes over, blocking access to fish. Water falling through the turbines of the dam to generate electricity wells up below the dam with such force that it doesn't freeze, offering access to fish. Therefore, wintering, fish-eating birds congregate in good numbers to dine on that finny prey.
The most abundant and obvious of fish-catching birds at Conowingo, blizzards of pale-gray and white ring-billed gulls swirl in the wind low over the river below the dam to watch for small fish in the up-welling water. When prey is spotted, the ring-bills drop to the turbulent water, beak-first, to grab fish in their bills. Meanwhile, other ring-bills, in groups, rest and digest between fishing forays on mid-river boulders.
Scores each of herring and great black-backed gulls also winter at Conowingo, where they catch live fish and scavenge dead ones. Both these species are larger than ring-bills, but the herring gulls are colored like ring-bills. The magnificent great black-backs, however, are white all over, except for black upper wings and backs, making them look something like bald eagles, except eagles have dark bellies. The goose-sized black-backs not only scavenge dead fish and other animals, but also steal fish from the ring-bills and other kinds of fish-catching birds. Herring and black-back gulls, too, rest on boulders in the river when not searching for food.
Sixty to over a hundred bald eagles, both adult and immature, winter at this dam. There they catch larger fish, ducks and other critters along the river, and scavenge the dead of those same species that wash up on boulders or shore. At any time during a winter day, these majestic eagles may be spotted perching on trees along the river, or mid-river rocks and power towers, or soaring on high.
To catch live fish, bald eagles swoop down to the water's surface and snare their victims with their long, powerful talons, without their bodies touching the water. Then they power-flap to a rock or tree to eat their catch.
Up to a hundred stately great blue herons stand on shores and mid-river boulders where they stalk live fish of various sizes in shallow water. These long-legged and long-necked birds generally are hard to see in bare trees and on rocks because they are gray, which camouflages them on those natural objects.
Several fish-catching birds of four species, including common merganser ducks, double-crested cormorants, common loons and horned grebes, dive under water from the surface to catch small fish. These birds are all built like boats (convergence) because of their living on water. The mergansers and cormorants winter in flocks on water in winter, but loons and grebes are more solitary. A field guide to birds may be needed to identify these similar water species.
Over a hundred each of turkey vultures and black vultures winter at Conowingo Dam in the Susquehanna because they, too, scavenge dead fish and other creatures. In winter, flocks of them roost overnight in trees near the river and perch on rocks and trees along the water during the day to watch for dead animals to eat.
Many crows winter at Conowingo Dam where they, too, watch for dead fish and other animals to consume, though they must compete with gulls, eagles and vultures for that food. But these intelligent birds persistently watch for opportunities and are able to scavenge carcasses in spite of larger competition for them.
Interestingly, crows, as well as gulls, also pick dead or stunned small fish that went through the turbines from the surface of the moving water. The crows, however, perch on trees to swallow their catches, then fly over the river for more.
Visit Conowingo Dam in winter to experience these interesting water birds. They are entertaining, and teach us about taking advantage of human activities, survival and competition for food.
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