Raptor Migration Through Pennsylvania
The Appalachian Mountains provide an ideal passageway for migrating raptors. This continuous chain runs north to south more than 3,000 miles through eastern North America, from Newfoundland and Quebec to Alabama. In early autumn, bald eagles journey through the Appalachians to spend the winter in scattered locations throughout eastern North America where rivers and lakes remain ice-free and food is available. Other migrating birds of prey may winter throughout the east and along Atlantic coastline or continue traveling south to the Gulf of Mexico and even Central and South America, like the broad-winged hawk, which may end its journey as far south as Argentina.
The Appalachians curve through Pennsylvania in long, narrow ridges that run in parallel lines, creating broad uniform valleys in several regions. In Pennsylvania, the mountains rise to moderate elevations, with a high point of 3,213 feet at Mt. Davis in Somerset County. The ridges and long summits like the Allegheny Front form "leading lines" for raptor migration, concentrating their numbers and giving opportunities for observations. Some raptors also will follow streams, especially if their diet includes fish and other aquatic organisms.
Forming the Appalachians' eastern edge, the Kittatinny Ridge runs 185 miles across Pennsylvania sweeping through 11 counties. It touches the border of northern New Jersey at the Delaware River and stretches almost to the Maryland line. Since the Kittatinny Ridge is the most southeastern ridge of the Northern Appalachians, raptors tend to congregate along this ridge on their way south. Many hawks, particularly Broad-winged Hawks, can fly south of these ridges where the landscape provides uplifting thermals and where they are seen from hawk watch sites such as Militia Hill and Rose Tree Park near Philadelphia.
The Kittatinny Ridge is recognized as a globally significant migration flyway and Pennsylvania's largest Important Bird Area (IBA). At least 16 species of hawks, eagles, falcons and vultures travel the Kittatinny Ridge as they migrate through Pennsylvania and more than 150 species of birds utilize the ridge during autumn and spring migrations and through-out the seasons. For migrating bald eagles and other birds, the ridge and surrounding forests and water-sheds provide critical resting and feeding habitat.
The mountainous also provides vital breeding grounds for many forest interior birds.
Autumn flights along the ridges change with weather and winds. Raptors depend on autumn's northwest winds that strike the mountains creating upward deflection currents which give birds lift. The highest numbers of hawks move through on strong northwest winds following cold fronts. A south wind produces fewer numbers, although birds fly lower, hugging the ridges, often just above the forest canopy.
The sun and clouds also play an important role for migrating birds, especially in the absence of wind. Birds of prey can move effortlessly across the sky by tapping into the energy produced by rising thermal air currents. On clear days, as the sun warms a patch of open ground, or a forest clearing or boulder field, a bubble of warm air rises taking any winged passengers upward. A soaring hawk or eagle can climb hundreds of feet in seconds without expending its own energy. Large groups of hawks, called ket-tles, reveal these invisible thermals with their tight circular flight patterns. As the thermal reaches its peak and begins to disintegrate, the birds simply lock their wings and glide away down the ridge to catch the next thermal. Birds of prey travel great distances this way, conserving valuable energy.
Timing of Autumn Raptor Migration
August – Early August brings Bald Eagles, Ospreys and Black Vultures past the ridgetops.
Late August – Red-shouldered Hawks, Peregrine Fal-cons, Northern Harriers, Sharp-shinned Hawks, Cooper's Hawks and Turkey Vultures begin migrating through.
September – Great numbers of Broad-winged Hawks are seen from hawk watch sites during September. September is also the peak month for Ospreys, Bald Eagles, Broad-winged Hawks and the start of peak numbers of American Kestrels.
October – Peaks of American Kestrels continue, Peregrine Falcons, Merlins, Sharp-shinned Hawks, Northern Harriers, Cooper's Hawks, Turkey Vultures and Black Vultures.
November – Black Vulture, Red-shouldered Hawk, Red-tailed Hawk peaks continue. November is also a good time to see Northern Goshawks, Rough-legged Hawks and Golden Eagles, which peak during late October and November.
December – Migration winds down through December, but many species continue moving south along ridges, including Golden Eagles; Rough-legged, Red-tailed and Red-shouldered hawks; Northern Gos-hawks; Cooper's and Sharp-shinned hawk;, Northern Harriers; Bald Eagles, vultures, and falcons.
Timing of Spring Raptor Migration
February – A few hardy Golden Eagles begin returning north from the Appalachian Mountain wintering grounds.
March – Many raptors begin the return journey to northern breeding grounds. It is common to start see-ing Bald Eagles, Golden Eagles, American Kestrels, Red-tailed, Cooper's, Sharp-shinned, Red-shouldered hawks and Northern Harriers. Ospreys return in late March.
April – Most numbers of migrating raptors peak in April, especially the far-ranging Broad-winged Hawks and Ospreys.
May – Spring migration peaks continue with Ospreys, Bald Eagles and Broad-winged Hawks.