These are the ultimate pigeon condos. The steel girders underneath bridges mimic rock crevices perfectly. They provide 360-degree protection from rain and hawks. That’s why you always see flocks under the freeway.

The classic. The gap between the top of the AC unit and the bottom of the window sash is the perfect "crevice." It’s warm in winter and shaded in summer. If you hear cooing right outside your bedroom window, check here first.

We know robins nest in trees and swallows build mud huts, but pigeons seem to appear out of thin air. The truth is, pigeons are architectural geniuses—and their nesting habits explain why they’ve taken over our urban landscapes so successfully.