GREENWICH, Conn. (AP) – For Brian Bielfelt, a typical “day at the office” means spending eight hours in a lush backcountry meadow staring up at the sky.

A 25-year-old biology graduate from Florida, Bielfelt toils five days a week as Audubon Greenwich’s “hawk-watcher,” a three-month position in which he scans the horizon for migratory birds of prey, from hawks to eagles, falcons to vultures, part of a regional effort to monitor the health of Northeastern raptor populations.

“This is my office,” he said, motioning to the verdant trees lining the sanctuary at the Audubon Center of Greenwich on Riversville Road. “People take time off to do what I call a job: Observing nature.”

For three years, Bielfelt has spent every workday between late August and late November documenting a variety of raptors migrating south over the Audubon Center’s Quaker Ridge to escape the cold northern weather and access larger food supplies in warmer climes.

Since his observation began on Aug. 20, Bielfelt said he has documented more than 23,000 raptors, which, at roughly the halfway point in the season, is already higher than last year’s overall tally of about 20,000.

That said, the frequency of sightings on a daily basis can fluctuate widely depending on weather, wind direction and migratory habits of various species.

By mid-afternoon on Oct. 9, for instance, Bielfelt and a group of recreational birders had spotted only 22 raptors. Compare that to Sept. 18, when hawk-watchers spotted more than 13,000 broad-winged hawks in a single windy day.

According to Bielfelt’s latest count, the most abundant type of raptor flying over the ridge this season has been the broad-winged hawk, which has been spotted 18,701 times. Trailing in distant second and third places are the sharp-shinned hawk, with 2,285 sightings, and the osprey, with 667. There have also been more than 300 sightings of the turkey vulture and the American kestrel falcon.

Spotting and identifying these various species can be a challenge.

Soaring at more than 3,000 feet, many raptors appear as little more than black specks on a vast blue expanse, and when flying at a distance of three miles away or more, can be difficult to spot even with binoculars, Bielfelt said.

To distinguish the various species, he relies – not on feather coloration, as many backyard birders do – but on shape, size and behavior.

For instance, while both the bald eagle and the osprey share a similar black-and-white feather coat, eagles typically cut a flat frame by flying with their wings fully extended, while osprey resemble the letter “M,” because of the crook in their wings.

And while both eagles and osprey soar at high altitudes, another species, the Merlin falcon, flies “low and fast,” often dive-bombing for prey on the ground as it migrates south.

“Merlins are like the Porsche Carreras of the falcon world,” Bielfelt said. “They flap their wings so powerfully and move so quickly, they can swoop down and fly over the trees before anybody gets a good look.”

To document these flights, Bielfelt records bird sightings and weather patterns on a clipboard throughout the day. At dusk, he retreats indoors to transcribe his notes onto a Web site, www.hawkcount.org, which collects similar data from bird-watching spots across the country.

The site’s information allows wildlife biologists worldwide to document changes in regional bird populations and migration patterns over several years, often yielding insights into the health of a particular species or the conditions of a habitat, Audubon Greenwich Director Karen Dixon said.

Still, birding isn’t just for the benefit of scientists, but local leisure seekers, as well, Bielfelt points out.

“It’s an activity that’s accessible to pretty much everyone. We have people coming out to the center every day – students on college break, retired firefighters, people on their lunch break,” he said, adding that some die-hard birders from the area have called in “sick” for several workdays during peak season to spend time at the ridge. “They get … what we call ‘hawk fever.”‘

Backcountry resident Allison O’Toole, 32, who was one of about a half-dozen people with their eyes to the sky at Quaker Ridge on a recent Thursday, said birding with Bielfelt had given her “more of an appreciation of nature.”

“You never know what’s going to happen when you’re out here watching,” she said.