Build a house for a specific bird. Build a birdhouse for a cavity_nesting bird that occurs in your region and lives in the habitat in which you plan to put in a birdhouse. (See Birdhouse Dimension Table to select a species.) Build the right size house and hole dimensions. Different species of birds require different sized houses and entrance holes. Inside dimensions must be large enough to accommodate the incubating biard and a brood of growing young. Entrance hole size is especially important. If the hole is too small, the bird you built the box for won't be able to get inside. If the hole is too big, predatory birds and mammals will be able to get inside and reach the nest, and cavity_nesting birds may not use the house.
Nesting Ledges. American Robins, Say's Phoebes, and Barn and Cliff Swallows will not use nest boxes, but they will next on platforms that are open on three sides. Platform nest ledges should be 6ν inches wide, 6ν inches long, and at least 8 inches high. Nest ledges can be easily fastened under the eaves of houses, buildings, bridges or on trees. They may be placed near a window where the behavior of birds using them can be easily observed. Place the nest ledge 8–16 feet above the ground.