Parts of southern United States, get to enjoy bluebirds year round but when spring starts to come around, a few from each of the three species of bluebirds will be heading north, as far as Canada, and the Mountain Blue Bird as far as Alaska.
The Bluebird is a timid, cavity-nesting bird, searching for hollows in decaying fence post, decaying trees or an old woodpecker holes. But competition for these nesting sites have increased since the introduction of the House Sparrow and European Starling in the 1800's. Both the sparrows and the starlings are cavity-nesting birds and are extremely aggressive birds. They will take over an occupied bluebird nest by destroying bluebird eggs, killing the nestlings and sometimes killing the parents.
Populations of all three bluebird species have severely declined in the early part of the 20th century.One important step we can take is to provide a nesting box to help bring back the bluebird population and to help the reduce nesting site competition. When buying a birdhouse for blue birds, make sure it is designed for bluebirds and if you are so lucky to have enough space, start a bluebird trail !