BETHEL – Last year, Bethel naturalist Jackie Cressy and husband, Allen, journeyed to Wolfville, Nova Scotia, just to see a chimney swift.

A chimney swift is a 5-and-a-half-inch-long, sooty gray bird that cements half-cup-shaped nests of twigs with its saliva to vertical spaces in buildings, chimneys and tree hollows.

But little did they know that just a short walk from Rivendell House, their bed and breakfast business at 16 Park St., chimney swifts have been frequenting a large chimney on Gould Academy’s Bingham Hall for years.

“We were stunned,” Jackie Cressy said Friday afternoon.

At midafternoon Thursday, the couple spotted about a dozen of the precision aerial acrobats swarming over their house.

She said the birds are gathering in large numbers now across the state, readying to begin their fall migration flight of 6,000 miles to the upper Amazon River basin in Peru, South America.

“Their numbers are very impressive. They chirp constantly and swirl around and around. You can’t miss the noise, it’s incredible,” she said.

But that’s not the magnet that drew the couple to the swallow-like bird.

Instead, she said, it is the phenomenon created when large numbers of swifts gather in a great flock for about 20 minutes, wheeling at dusk, only to disappear down a chimney.

“It’s so funny to watch them see if it’s their turn to enter, but when they all do, going in, it’s like a vaccuum. It’s a sight to behold,” Jackie Cressy said.

The whole phenomenon, she said, can last half an hour.

“They swirl all together, then, whoosh! they break apart, come back together, swirl, and then come in at an angle over the larch trees and into the chimney, dropping in in 10s and 20s,” she said.

Cressy said volunteers across the nation tonight will begin counting chimney swifts as they enter roosting spots.

Dubbed A Swift Night Out, the conservation survey is a segment of the 2004 Chimney Swift Roost Monitoring Project.

The Cressys welcome any volunteers to join them in Bingham Hall’s rear parking lot at 7:45 p.m. tonight.

The magic begins shortly after 8 p.m.

Thursday night, the couple counted between 230 to 330 birds, using an estimating method.

“We take a can and a handfull of pennies, and estimate the birds by tens, and drop a penny in the can for every 10 birds you see. Some people use an athletic lap counter with one click indicating groups of five, 10 or 20,” Jackie Cressy said.

Reflecting on their birding trip to Wolfville, she said she belives that Bethel has more chimney swifts.

“When we were in Wolfville, we kept track of them every night. For Wolfville, the swifts are a major tourist attraction, so we’re missing something here,” she added.