Gloves on, field scopes pointed toward a mountaintop at Snickers Gap, the three hawk-watchers swap bird intelligence.

"There's a hawk at locust," says Todd Day, 30, meaning that the bird is near a locust tree.

"Glass up," he yells, and the other man and the woman at the Gap nudge their scopes up a few inches--roughly the length of the lenses of their scopes.

In this way, they will try to get the hawk in their field of vision while the creature is winging by on its way to winter nesting grounds in Central or South America.

It's raptor migration season, and the raptor-obsessed are at it again.

The bird-watchers are volunteers with the Hawk Migration Association of North America who congregate in a parking lot at Snickers Gap every day during the migrating season, September through November. They are looking for raptors--birds of prey that eat fish, insects and other birds.

The volunteers gather raptor data on printed forms they carry on clipboards, noting the particulars of each bird sighted: time of day, wind direction, temperature, visibility. They indicate whether they saw an osprey, eagle or hawk--or any of a dozen or so other birds of prey that typically use the thermals of the Blue Ridge Mountains--currents of hot air that blow up the mountainsides--to help them soar and float along their migratory routes.

Thousands of raptors pass through every season, and the middle of September is a particularly busy time: 4,500 of the birds--mostly broad-winged hawks--flew over Snickers Gap on Sept. 19, Day said.

Snickers Gap, the volunteers said, was selected nine years ago as the premier location in the Washington region for "raptoring." The Gap has good thermals that attract a lot of birds, and--for humans--there's a parking lot conveniently located at Routes 7 and 601 not far from Bluemont.

Raptor fans like nothing better than to while away the day telling about other birds they've seen in other years and what kind of scope they were using when they made the sighting.

"There's a sense of camaraderie that you don't get in other birding," said Day, 30, who drives an hour from Culpeper County three or four times a week to stand with the others at Snickers Gap. "You don't have to be quiet. You can talk. We have a lot of fun."

Novice raptor-watchers are easy to spot: They mistake vultures for hawks, the birders said. They show up with binoculars instead of the more powerful scopes and miss out on the interesting stuff--rough-legged hawks, peregrine falcons.

But everyone is welcome. Learning is part of the fun, the birders said, and with raptors, there's always some new fact you never knew.

Deborah Denice, 38, a federal government employee, said the learning was one of the things that drew her into the subculture of birders and helped her rationalize the purchase of a $800 Nikon field scope.

"You finally do it when you see that somebody next to you is seeing something better than you," Denice said.

To aid in spotting birds of prey, the raptor-watchers at Snickers Gap have worked out a complicated system of letting each other know where the birds are. Instead of saying, "To the left" or "Up there," they call out the names they've assigned to every tree formation and landmark. Three trees on a ridge line, for example, are called "Minnie Mouse" because the birders decided that they make a shape resembling the Disney character.

Hawk-watching is not for the fair-weather birder. These volunteers show up in any weather and sometimes stand behind their scopes for half a day. Bathroom breaks are in the woods--but hawk-watchers hate to risk leaving even for that. It doesn't take long for a bird to fly out of the range of their scopes, and many a hapless birder has missed out on seeing a rare bird while on a potty break.

Sacrifices are made.

"It's a lifestyle," said Bill Harry, 64, a retired aeronautical engineer with the Navy who lives in Oakton and keeps a peregrine falcon that was bred in captivity.

Everyone can give the precise day on which their curiosity grew into a full-blown obsession.

Day, manager of a home medical equipment company in Jeffersonton in Culpeper County, was already "into birds" when he moved from Boston seven years ago, met a couple of hawk-watchers and became hooked after his first trip to the Gap.

Last year, he became the chief scheduler of volunteers, the collector of bird-sighting data sheets and the one who feeds the data into a computer spreadsheet. At the end of annual raptor migration season in November, he will send the information to the Hawk Migration Society.

He does it all strictly on a volunteer basis. "I'd rather be watching birds, but no one wants to pay me to do it," Day said.

Denice got hooked on a vacation in Blackwater National Wildlife Refuge in Cambridge, Md., six years ago. She and her boyfriend--who became her husband through their shared interest in birding--saw some people bird-watching, stopped to talk and learned that if they took the time to look, they might see bald eagles along the George Washington Parkway.

"We did that and we came out here, and that kind of did it," said Denice, who took a personal day from work Thursday to race up to Snickers Gap.

"Wait till you see a bald eagle migrating over the mountain," she said. "Then you'll know."

CAPTION: Bill Harry is reflected in a car window as he watches for raptors with his binoculars, his spotting scope nearby.

CAPTION: Volunteers for the Hawk Migration Association of North America gather Thursday at Snickers Gap to look for migrating birds of prey. Todd Day and Deborah Denice, background, search the skies.

CAPTION: Bill Harry sets up his equipment for a day of bird-watching at Snickers Gap. "It's a lifestyle," he said of his hobby.