Why do birds use birdhouses in general? Birds are looking for nesting cavities in which to build their nest. Song birds that use tree cavities are not capable of creating their own nesting cavities because their beaks are specialized for hunting insects or gathering seeds. In an undisturbed ecosystem songbirds such as wrens, chickadees and nuthatches look for tree cavities created by other birds such as woodpeckers.
Tree cavities provide shelter for birds from predators. There are two kinds of cavity nesters: those that create their own nesting cavities (primary cavity nesters) and those that use pre-existing cavities (secondary cavity nesters). Insects or pathogens have also been found to assist in formation of cavities that are used by cavity nesters.
The amount of forested land in North America has greatly decreased over the last 200 years due to agriculture and urbanization. Many trees that have nesting cavities are not structurally sound, and are cut down in to prevent damage to property. As a result, there is a shortage of suitable nesting sites for both primary and secondary cavity nesters. Birdhouses have been used as a solution to the lack of natural cavities.