BETHEL – Several hundred chimney swifts were spotted entering a large chimney to roost Saturday night at Gould Academy’s Bingham Hall.

About 25 volunteers joined Bethel naturalist Jackie Cressy and her husband, Allen, to count the birds for the 2004 nationwide Chimney Swift Roost Monitoring Project.

“We counted roughly 500 birds entering the chimney, so it looks like they are massing for migration,” Jackie Cressy stated in an e-mail. “We plan to go regularly to watch the numbers and pattern of entering, and their last’ day here.”

Allen Cressy said Tuesday that other Bethel residents believe the birds, which have doubled in numbers since Saturday, are to begin migrating en masse by Thursday, Aug. 19, or Friday, Aug. 20.

“We will be tracking it over the next several days,” he said.

A chimney swift is a 5-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.

Jackie Cressy said the birds spend nearly all of their time flying, except when they are at their nest or roosting for the night.

Swifts migrate 6,000 miles to the upper Amazon River basin in South America.

“It’s quite interesting to think that they’ll all be gone from here in a few days,” Jackie Cressy said Tuesday.