Peregrine Falcons once nested almost exclusively on lofty cliffs; they were uncommon residents in populated areas like cities. Now they can often be found atop tall buildings and bridges, sometimes in nesting boxes provided by human friends. These swift hunters need a towering roost to spot their prey. In the wild, Peregrines typically scrape a nest in the dirt of a crag or a cliff, usually near lakes or rivers favored by ducks and other waterfowl. On a building they quickly adapt to a man-made nest box with wall-to-wall gravel. Unfortunately, the urbanized Peregrines face new dangers. Some are confused by skyscraper windows and try to fly through them. They are sometimes slammed into buildings by high winds, forced to land in traffic or injured by flying into power lines.