We get the Great-tailed variety here (which I had not seen until I moved to Texas; chalk up another on my life-list, which has also recently added scissor-tail flycatchers, roadrunners and egrets). They began swarmng in February - and seemed, like the ones you encountered, to favor the most crowded intersections, especially if there were overhead wires available. Another crowd hung out in the trees at the grocery store parking lot, pooping on cars, foraging for scraps, and making noises like R2D2 on steroids.

Most of them, but not all, have gone farther north. Good riddance, I say.

(I suppose the swarms return in the fall, on their way to Mexico -- I can wait.)