Even in a mature yard that is well planted with trees, dense vines and shrubs, there is likely a shortage of suitable nest sites. This is especially true if large number of local birds have been maintained through the winter by food supplied at feeders. It's so easy to follow the bird family life unfold if you put up a well placed birdhouse. A birdhouse should be placed away from the worst effects of the sun and rain. It must be secure enough not to fall down, but it does not matter if it wobbles a bit.
You must resist the temptation to visit a birdhouse or any other nest during the laying season. The laying period is a very sensitive time, and some birds desert their nest if it is disturbed. Visits also make the nest more vulnerable to predators who will follow the trail of your scent, out of curiosity.
Research has shown that a single visit to a robin or bluebird nest increases the chance of both dessertion and predators. If well groomed nestlings are disturbed, they are likely to erupt out of the nest in a panic. If they do, gently place them back into the birdhouse and stuff the entrance with a handkerchief until they settle down. There are about 80 species of birds that nest in cavities and are candidates for birdhouses.