Commentary: Keep an eagle-eye to the sky for migrating raptors

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As the days grow shorter and cooler, the skies fill with birds migrating to warmer climates for the winter. The Chesapeake Bay watershed lies in a major migration path known as the Atlantic Flyway. Mountain chains to the west and the Atlantic Coast to the east channel millions of migrating birds through the Bay region. Among these fall travelers are eagles, hawks and falcons, commonly known as raptors.

Raptors begin their annual southward migration just prior to the fall foliage color change. The earliest migrants may not be noticed. Juvenile birds lead the way, beginning their migration in September. Adults generally wait until late November to join the southbound flight.

As they approach the Bay, the topography of the land causes some migrants to funnel along the coast, while the others are steered along the mountains.

Mountain ridges are great spots to see raptors. The best days are when a cold front pushes a north, northwest or westerly wind against the western face of the mountain ridge. The combination of cooler air and strong wind allows the bird an effortless “ride” southward.

The most common group of hawks seen from the ridges is of the genus Accipiter. Characterized by their long tails and short, rounded wings, accipiters, such as the sharp-shinned hawk (A. striatus), northern goshawk (A. gentilis) and Cooper’s hawk (A. cooperii), can be seen gliding along the mountain treetops. These hawks dominate the sky during most of October.

The buteos, or soaring hawks, include species such as the broad-winged hawk (Buteo platypterus), red-shouldered hawk (B. lineatus) and red-tailed hawk (B. jamaicensis). Broad-winged hawks congregate in groups of 100 birds or more, called kettles, migrating in September. The rest of the buteos travel later, peaking in November, when temperatures begin to drop in earnest. Red-tailed hawks are the most common migrant during this period. These large robust hawks are seen hesitating along the ridge, making sudden stops into the trees, as they attempt to capture squirrels.

On occasion, a golden eagle will make a showing, usually around late October following a strong cold front. Wind conditions that peak at 25 mph will increase your chances to witness such an event.

To observe the hawk flights along a mountain passage, head west into Appalachia. The west-facing ridges in Pennsylvania, western Maryland and Virginia provide excellent opportunities to see the southbound migration.

The coastal migration route is different than that of the mountain ridges, in that there are wide water crossings — namely the mouths of the Delaware and Chesapeake bays — which tend to concentrate traffic as the raptors wait for ideal wind and strong thermal updrafts before venturing out over the water. That’s what makes Cape May, New Jersey, and Cape Charles, Virginia, ideal raptor-spotting places. The narrowing landmass funnels the migrants together, and the water gives them pause.

“Raptors that use a coastal migration corridor route are slowed and concentrated at the southern points of (Cape May and Cape Charles), as the landmass ends,” said biologist Craig Koppie, a raptor specialist with the U.S. Fish & Wildlife Service. “Multiple species of raptors can be observed in a holding pattern or swarm, as they fly in circles and even head northward. When weather conditions are not beneficial for flying, raptors (wait for) thermals that provide them the greatest lift to fly over vast bodies of water.”

Falcons are one group of raptors that migrate along the coastline. Birds of the Falco genus are characterized by long, pointed wings and long, narrow tails. The American kestrel (F. sparverius), merlin (F. columbarius) and peregrine falcon (F. peregrinus) favor the wide-open spaces of the coast. The northern harrier (Circus hudsonius), sometimes called the marsh hawk, is also seen along the coastline. The fact that the coastal habitat attracts many other bird species is key for the raptors; smaller birds are a critical food source for them.

Ospreys and bald eagles also favor the coastal and estuarine flight paths. But ospreys are largely gone by October — as far south as South America — and many bald eagles are year-round or winter-only residents of the Bay region. If you see a bald eagle this time of year, it’s likely a year-rounder or just arriving for the winter.

As with the birds that follow the mountains, you can tell the coastal migration is nearing the end when adults join in the southbound flight, usually toward the end of November. In addition to Cape May and Cape Charles, the barrier islands of Assateague, Maryland, and Chincoteague, Virginia, are good spots to see these beautiful birds of prey on their annual journey south.

Kathy Reshetiloff is with the U.S. Fish & Wildlife Service’s Chesapeake Bay field office in Annapolis, Maryland. She is a columnist for Bay Journal, where this was first published.