RED WING — Just before dusk on evenings in August, a handful of chimney swifts drop down and circle above the chimney of St. John’s Evangelical Lutheran Church on East Avenue.

Quickly, others join in. In the last moments of light, the flock contains hundreds of rapidly chirping birds, swooping low near the chimney, then veering off and soaring high, creating a swirling chaos of wings.

They edge closer and closer to the chimney until one bird drops inside. Then a second. Soon a line of swifts seem to fall from a point five or six feet above the roof and dive into chimney. Within two or three minutes, the flock is gone, and the sky is still and quiet.

“They are roosting,” said Lori Naumann, information officer in the nongame wildlife program of the Minnesota Department of Natural Resources in St. Paul. “There will only be one nest in each chimney, so even if there are hundreds of them roosting in there, there is only one nest for one bird.”

Naumann said many people cover their chimneys to keep birds and other animals out. Swifts have to search to find open chimneys, and they prefer brick and mortar.

“That way they have some sort of rough edge to hang onto, somewhat like bats,” Naumann explained. “They are tough little birds.”

The birds hang on the inside walls of the chimney, but they don’t cause any harm, Naumann said.

The swifts roost inside the chimney through the night and early morning, waiting until the air is warm enough that the flying insects are out. Then the swifts leave the chimney and fly throughout the day, feasting on insects.

American ornithologist Roger Tory Peterson described a chimney swift in flight as a “cigar with wings.”

Naumann noted that “once you know their shape, if you look up during the day, you will see them quite often flying around, eating flies and other bugs that are in the air. They are strictly insect eaters.”

Chimney swifts stay in Minnesota and Wisconsin until late August or mid-September. According to Naumann, they migrate to Columbia, Ecuador, and Peru on the western coast of South America. When they return to the Midwest, they often use the same chimneys year after year, as they migrate.

Frontenac State Park, and other locations, have constructed false chimneys designed to attract chimney swifts. Naumann said she has considered building one in her own backyard, so she can watch the swifts, and added that fellow DNR employee Carrol L. Henderson wrote a book called “Woodworking for Wildlife," which has construction plans for chimneys as well as other projects for birds and animals.

The Audubon Society keeps track of many locations where chimney swifts roost, and they send members out to count the birds. The numbers they record become part of the yearly count for the Minnesota Breeding Bird Atlas.

“It’s not easy,” Naumann said. “You can’t be distracted. You have to keep track and count them just as they drop to the edge of the top of the chimney.”