The Bluebird population had declined by 90% by the late 1960s
Here are some of the reasons for the decline:
Loss of Nesting Sites
|House Sparrows are a major reason for the decline of bluebirds.
The introduction of the House Sparrow in 1850 and the European Starling in 1890 caused major trouble. Rising populations of these adaptive, aggressive, non-native birds commandeered nest sites, leaving the bluebirds homeless.
Loss of Habitat
With increased industry, people moved to cities, and farms reverted to forests or were developed into housing or commercial properties. The Eastern Bluebird lost its required open area habitat.
Fencing material changed from wood to plastic and metal. Rotting fence posts once supplied abundant nesting cavities. Pesticide use, particularly in orchards, poisoned bluebirds. Increased removal of dead trees eliminated cavities.
Fortunately, by the 1970s bluebird enthusiasts began major efforts to reversed the bluebird's decline by building and mounting thousands of bluebird nestboxes. Now bluebirds are returning.