Pigeons and starlings aside, federal law prohibits disturbing a bird nest before the chicks fledge, says pest-control pro Tom Scollins. Once they're gone, however, you can remove a nest and make the spot less attractive to future generations. "Birds are cavity nesters," he says. "They look for spots that are protected from sun, rain, and predators." Repair any openings in the fascia, or they'll find their way in. They also flock toward gutter downspout returns that are near horizontal. You can curb that urge by replacing the downspouts with steeper runs. For ledges and cozy spots you can't eliminate, install bird spikes, but make sure to get the right size for the birds you're dealing with. "Small birds will nest between large spikes, and large birds will nest right on top of small spikes," Scollins says. So first identify the species, then order spikes sold specifically for those birds.