Clouds aren’t the only thing swirling around in the skies this week: The Vaux swifts are back in town.

Each September, some 30,000 of the tiny winged migratory critters roost in the towering smokestack of Chapman Elementary School in Northwest Portland, the largest such gathering of Vaux swifts in North America.

With seemingly as many Portlanders turning out to view the birds whirl through the sky and dive-bomb, enmasse, into the school’s chimney, it might also be the largest display of bird-lovers in the country.

Needless to say, the whole scene, which tends to peak at sunset, can be dizzying. So to help bring things into focus, Audubon Society volunteers will be manning the school’s lawn for SwiftWatch 2010 just about every night in September.

Feel free to stop by and borrow a pair of binoculars, or chat them up about swift trivia. (Did you know swifts have been clocked at 100 mph? Or that they can’t actually perch on branches?)

To help you brush up the Vaux swift phenomenon here in Portland, I dug up this Oregon Field Guide episode about the little black birds from back in 2000.

(No word on whether that black swift hat is still available).