Inaccessibility (for you, not them)
The most important thing birds need in a nesting location is safety. They want to lay their eggs and care for them in a place where opportunistic predators can’t harass them. Luckily for birds, they can fly. Most birds make their nests high up in the air simply because it’s tough for predators to reach them there. When you think of nests, you probably picture a cute little nest in the nook of a tree, but real birds aren’t as picky. Any nook, ledge, or cranny on your home could be a surface where a bird could build its nests. Look in window sills, gutters and downspouts, railings, slanted roofing, shingles, corners--really anywhere with enough space to cram some nesting material will do just fine.
Concealment
Birds have the flying advantage over most predators, but not all of them. Hawks, owls, and other flying predators will happily scoop up an egg or two for breakfast if they have the chance. If mom gets distracted caring for her kids, they’ll even eat her, too! To deal with flying predators, birds look for places where they can hide or at least partially cover their nests. There’s a reason the cliche of the nest in the nook is ubiquitous; a nook provides great cover in every direction but one. Birds look for high places in homes where they can nest. They’ve been known to build inside of plumbing ventilation shafts, chimneys, garages, damaged shingles, or gutters. The tighter and harder to spot a place is, the better protection it will give them and their vulnerable eggs.
Food
Even nesting birds gotta eat. Their babies really gotta eat. They’re going to be retrieving food and bringing it back to the nest over and over again, so they really need that food to be close. Building a nest far away from food is like living an hour away from a grocery store, only birds don’t have refrigerators or delivery trucks. Also, every time they go out they might get eaten themselves. Obviously, early birds would love to get their beaks on some worms, but their diet isn’t restrictive. Nuts, berries, small insects, garden vegetables and fruit, and seeds are all prime bird food. If you have a tree in your yard, the seeds or nuts it drops would make it very attractive to a nesting bird or three. If you or your neighbors have bird feeders, well, that’s obvious.
