Bald eagles return to the Hudson Valley

The morning mist lifts from the Hudson River, and somewhere in the tall sycamores along the bank, a bald eagle (Haliaeetus leucocephalus) shifts on its massive nest. The sound carries across the water, a brief rustle of sticks and branches that have been woven together over months of patient construction. If you are walking near the river's edge, stop and scan the canopy. The white head and tail feathers catch light even in shadow.

Fifty years ago, this sight would have been impossible. DDT had thinned eggshells so severely that bald eagles could not successfully reproduce. The Hudson Valley lost its eagles entirely. But the birds that hunt these waters today represent one of conservation's most tangible successes. Each pair that nests along the river is proof that ecosystems can recover when the chemicals that disrupted them are removed. The eagles returned gradually, first as wandering juveniles, then as breeding pairs. Now they are residents again, as integral to the river as the tides.

The eagle perched above the water is watching for movement below. Double-crested cormorants (Nannopterum auritum) dive and surface in the shallows, their sleek black forms disappearing for thirty seconds at a time before emerging with fish clasped in their bills. The cormorants are skilled underwater hunters, but they are vulnerable when they surface. An eagle can strike from above with enough force to stun a cormorant, then carry it to shore. This is not the eagles' only hunting strategy, but it is one that the cormorants know well. They dive closer to fallen logs and overhanging branches, places where an eagle's approach would be obstructed.

The relationship between these two species extends beyond predator and prey. Both nest in colonies, though eagles maintain much larger territories. A single eagle pair may claim several miles of riverfront, while cormorants crowd together on small islands or in dead trees that can support dozens of nests. The eagles benefit from this arrangement. Cormorant colonies attract fish to the area, and the constant diving and surfacing creates opportunities for the eagles to hunt. The cormorants, in turn, benefit from the eagles' presence in an unexpected way. Eagles are territorial and will drive other large predators away from their nesting areas, creating safer zones for smaller waterbirds.

The nest above you holds eggs or young chicks, depending on how early the pair began breeding this season. Eagle pairs return to the same nest year after year, adding new material each spring until some nests weigh more than a ton. The young will not fledge until midsummer, but already the adults are spending more time hunting. A growing eagle chick requires nearly a pound of fish each day. The parents take turns, one remaining at the nest while the other patrols the river. Their hunting grounds extend from the tidal marshes downstream to the rocky shallows upstream, wherever fish concentrate and the water is clear enough for the eagle's sharp eyes to penetrate.

Close your eyes and listen to the water against the bank. The sound is constant but never quite the same, shaped by wind and current and the wakes of boats passing in the channel. When you open them again, look for the flash of white feathers against the green canopy, the broad wings that span eight feet when the eagle finally lifts from its perch and begins another hunt over the Hudson's recovering waters.