Eastern bluebirds were once as common as robins. But between the 1920s and 1970s they almost became extinct. Their decline was due to a variety of reasons: habitat loss, dead tree (snag) removal, pesticide use, even house cats. But one of the main culprits was the introduction of two other birds - House Sparrows and European Starlings - that aggressively out competed the bluebirds for nesting sites. (Bluebirds tend to be shy, timid birds).
Bluebirds depend on abandoned cavities, made by woodpeckers and other cavity creating birds, for nesting sites. In 1978, a group of concerned citizens and birders form the North American Bluebird Society (NABS) began putting up Bluebird nesting boxes. They set up a network of trails, and trained volunteers to monitor population numbers and health. The Eastern Bluebird population rebounded, escaping extinction. NABS still works to protect bluebirds and all native cavity nesters.
To learn more about bluebirds, NABS and how to build a bluebird house visit: