What could bring crowds of people out after sunset on a September evening to stare at  ... a chimney? Swifts, of course! Scores of swifts form a funnel-shaped cloud above the right kind of chimney, then they begin their descent. First one, then a few more, then dozens, then hundreds swirl right down into the chimney. You can help Chimney Swifts and Vaux's Swifts by providing a roosting tower.

More info and transcript at BirdNote.org. 

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