Such are the graceful aerials of raptors in the Marin Headlands throughout fall. During the season, tens of thousands of hawks, falcons, vultures, and even a few eagles drift down the Pacific Coast to warmer climes—some headed as far south as Argentina. En route, the Marin County peninsula funnels them into a dense concentration at its tip.

As autumn sun shoos summer's fog away, the place to be is the aptly named Hawk Hill. Although the raptor migration hits its peak in late September, smart hawk watchers visit from October to mid-November, when skies are clearest. On September and October weekends, Golden Gate Raptor Observatory naturalists, volunteers, docents, and bird lovers congregate for an annual raptor rap—public invited.

"One undocumented sharpie," calls out a spectator.

"Two TVs," says another.

A woman, clipboard in hand, dutifully records all such pronouncements in this arcane lexicon, the secret language of hawk watchers. Sharpie is short for sharp-shinned hawk; TV, for turkey vulture. Working in daily shifts, about 150 volunteers stand guard to catch the migration's earliest and latest installments, from mid-August to mid-December.

It's a rough count, admittedly. Some raptors may be tallied more than once, as the same birds come in and out of view over a day, or several days, or even weeks. The counters may miss others, especially when the thick Pacific fog hunkers on the hilltops, a holdover from summer.

Nonetheless, the numbers are impressive: 36,646 raptor sightings in 2002, nearly 70 an hour, with an average of 50 an hour over the 1992-2001 seasons. The volunteers are trained to see distant birds, but a casual observer spots a fraction of the count. Still, most see red-tailed hawks, Cooper's hawks, and sharpies. They hang motionless in the air just above ridgelines, held by updrafts. They flit among the trees and brush. They circle. They soar.

Bill Prochnow, design director at the Golden Gate National Parks Association, delights so much in these creatures that he's been a raptor volunteer for 19 years. He explains the successful tracking program here: Volunteers set out nets with lures, then lurk in blinds to catch the birds and place coded metal bands on their legs. Though the bands generally aren't seen again unless a raptor is found injured or dead, such cases are numerous enough to be useful. "The information on the found bird goes to a bird-banding lab in Laurel, Maryland," Bill says. "They track these programs across America. Ornithologists can see patterns of migration emerge, and gather other useful data such as the general state of the birds' health."

Volunteers usually release the newly banded birds quickly. For this afternoon's demonstration, however—given at 1 p.m. every Saturday and Sunday in September and October—the bird must wait for showtime. From his daypack, Bill pulls out two soup cans, stuck end to end with duct tape. Inside is a male Cooper's hawk caught minutes before. Bill slowly, carefully reaches into the can.

"Some banders liken this to putting your hand down a garbage disposal," Bill comments, acknowledging the hawk's sharp talons. Holding its legs together with one hand, he just as carefully withdraws the bird and explains the banding application.

The hawk is relatively calm yet intense, with its flexing talons and stabbing beak and fierce, restless eyes: a picture of power and purpose. Bill lifts his arm, and the hawk instantly sails away, like a kite cut loose.