Interior Area

• The bottom of the bluebird house should be a square that measures 5 inches on each side. This will give the nesting birds plenty of room to comfortably lay eggs while still feeling snug. The back of the house should be 10 3/4 inches high, while the front should only be 9 inches tall to allow for a slanted roof. Bluebird nests will hold between four and seven eggs, so the area inside the bird house must be large enough to hold not only the eggs but the young birds until they leave the nest when they are about 3 weeks old.
  
  

Space Between Boxes

• To attract more than one family of bluebirds, each family must have sufficient area in which to establish its territory. Depending on the species of bluebird in the area as well as factors such as competition from other species, the area between boxes varies. For the eastern bluebird, nesting boxes should be at least 375 to 450 feet apart, while mountain bluebirds need a larger area of at least 600 feet. The western bluebird is the most tolerant and has commonly been seen nesting in boxes 300 feet apart. Typically, nesting boxes should be facing in opposite directions to further increase the feel of space and open territory for each family of birds.
  
  

Space Between Competing Species

• Bluebird houses will often attract other birds such as sparrows and wrens. While these birds are well known for moving into bluebird houses and building their own nests, when there is plenty of shelter available, birds of different species will generally nest near without conflict. Building a pair of birdhouses can be an effective way of keeping other birds happy while still attracting bluebirds. The second, nonbluebird house can be of a different, more generic style, and can be mounted anywhere between five and 25 feet apart. This will give each family sufficient area to establish its own territory, while discouraging the other birds from nesting in the bluebird house.
  
  

Immediate Surroundings

• For the nesting box to be attractive to a pair of bluebirds, the entrance to the birdhouse should ideally be facing a tree, bush or shrub no more than 100 feet from the nest. When the parents are teaching the young to fly, this will give them an appropriate place to aim for that will keep them safe from any predators that might be on the ground. The boxes should be at 3 feet above the ground, preferably higher, on a smooth metal pole. This area will act as a safety zone, keeping birds safe from predators like cats and raccoons.