Peering through the eyepiece of his tripod-mounted spotting scope, Peter Low scanned a string of ridges and peaks that stretched between Mount Jefferson and Mount Hood from a vantage point he set up due east atop Green Ridge in the Deschutes National Forest.

“I've got three accipiters to the right of the skinny snag," he shouted.

When he made this announcement, we — as in myself, my wife, Meryl Ibis, and some volunteers from the East Cascade Audubon Society and the High Desert Museum — trained our binoculars on a dead fir tree that stuck out on the horizon, and waited for a set of birds to soar through the air.

Almost immediately, the trio of sharp-shinned hawks thrust above the horizon and rode a series of air currents flowing up Green Ridge's western slope. On outstretched wings, they headed south over the 4,400-foot-high ridgeline to their winter homes.

“We've got a counter," Kevin Smith said as he watched one of the three hawks fly past.

For the next two weeks, teams of volunteers from the High Desert Museum and the East Cascades Audubon Society will meet up at the Indian Ford Campground northwest of Sisters and head out to their viewpoint to count the raptors that fly overhead (see “If you go," Page B6).

The data collected about the migrating raptors will be shared with a number of groups, including the Utah-based HawkWatch International, in order to learn more about the birds and protect them so that others may watch their flights in the future.

The viewpoint

With a wingspan of 23 to 27 inches, sharp-shinned hawks are some of the smallest birds of prey that fly over Central Oregon during the months of September and October as they migrate south for the winter. Other raptors that have been spotted flying over Green Ridge include bald and golden eagles, kestrels, merlins, peregrine falcons, turkey vultures, Cooper's hawks and red-tailed hawks.

Low said it's impossible to tell where the birds are coming from and where they'll end up when they've finished their migration. Most of the raptors head south from areas in the Pacific Northwest and Canada to Central or South America, he said. But there are a few birds, like a rough-legged hawk he spotted in October, which spend their summers in the Arctic tundra and spend their winters in the relatively warmer climate of the northern United States.

“We only count the birds that pass this position," Low said. He explained that this way we could tell the migrating raptors — the ones that flew over Green Ridge on their way south — from the locals, or resident raptors that lived in the area and were just out for a quick flight.

Low and the other volunteers planned to stay at their viewpoint until 5 p.m. — the Pole Creek Fire started that morning may be affecting the viewpoint because of its smoke — as they gazed through their binoculars and swapped stories about previous hawk-watching trips.

But Meryl and I, who between us only had one set of binoculars and a camera lens that wasn't powerful enough to catch the birds, decided we'd been on top of the ridge long enough after a couple of hours and headed home. We probably would have stuck around much longer had we brought a comfortable chair and some better equipment — and come on a day closer to the migration season's peak when the raptor counts were much higher.

My conversation with Joseph Dane, the development director for HawkWatch International, might also have encouraged us to stay a bit longer.

The count

Amanda Wilhelm, of the High Desert Museum, said she counted nine raptors — six sharp-shinned hawks, a turkey vulture, a Cooper's hawk, and an American kestrel — during the time Meryl and I were up on the ridge.She promised we'd see 10 times as many birds later in the month.

But she didn't tell us what happens with the counts once we came down the mountain. Luckily, my conversation with Dane, whose group manages nine official hawk watch sites in the Western United States and collects data from dozens more, filled in the missing pieces.

“We're looking to see if there are any major shifts in raptor populations," Dane said.

HawkWatch International can do this because bird watchers at its official sites — like the one atop Bonney Butte in the Mount Hood National Forest — have been monitoring their raptor populations for at least 10 years and have enough data to tell when something is different. The Green Ridge site has been in operation for about seven years. While it shares information with HawkWatch International, it is not considered an official part of the program.

Once they have a steady picture of an area's raptor population that's been gleaned by counting birds at HawkWatch's migration sites and by tracking the ones it has banded with special tags, he said it's possible to tell when something's not right and is causing the country's birds of prey some problems.

Significant drops in the bald eagle and peregrine falcon counts HawkWatch International monitored in the late 1970s and the early 1980s helped the organization track the effect of pesticides on bird populations. The counts are currently being used to discover how cheatgrass, an invasive species, is affecting raptor populations in the West and to determine where wind farms should not be located.

“There's a lot of work to be done," he said. “American kestrel populations are dropping and we still haven't figured out why."

Knowing that I was part of this work and, in some limited fashion, helping to solve the mystery surrounding the American kestrel, a species of falcon with a wingspan of only 20 to 24 inches, probably would have convinced me to stay on top of that ridge a little bit longer.