Hawks migrate along the Blue Ridge Mountains, just 20-some minutes from our house. Pat and I have been gawking at them since the late ’70s, during which times we’ve been on the mountain when many birds were visible. Yesterday was one of the days when there were lots—thousands.
When they migrate, the birds (Broad-winged, Cooper’s, Sharp-shinned, Harrier, Kestral, and other hawks; Osprey and Bald Eagle, and other big ones) gather at places where warm air is rising (thermals) and ride the up-draft to gain altitude; when there are lots of birds in a group, they look like a kettle, narrower at the base and wider at the top. Then they stream out of the kettle and continue southward. Yesterday, when they streamed out, there were so many birds going south that, at 4-8 abreast, the stream looked like a river.
One can learn about the mirgration Hawk Migration Association of North America (HMANA). HMANA maintains a Web site that allows one to locate sites where migration counts are conducted. The data shown in the image above come from the Rockfish Gap (Afton, VA, US) site where we watched the river flow yesterday.