• Bluebird houses have helped to increase the species.bluebird image by Dwight Davis from Fotolia.com
  
  Modernization has led to a decline in natural nesting cavities for bluebirds. Starlings and sparrows are also cavity-nesting birds that are aggressive and compete with bluebirds for nesting places. This has led to a decline in bluebirds since the 1970s. Bluebird houses have played a major role in restoring the bluebird species throughout the United States. Bluebird houses have special requirements to make them predator-proof and undesirable to starlings and sparrows.
  
  

Common Characteristics

• All bluebird boxes have a few things in common. They are made of cedar or redwood, well ventilated, watertight, and have a means of drainage in the bottom. Never use treated lumber due to its toxicity. A light-color stain can be used on the outside only. Never place a perch on a bluebird house, as this is an invitation for sparrows, starlings and wrens.
  
  

Western Bluebird Houses

• Western bluebird nesting boxes have a 5-by-5-inch floor, a 9-inch ceiling, an entrance hole of 1 1/2 inches across, and a hinged roof along with all the common characteristics listed above.
  
  

Southern Slotted Bluebird House

• This type of bluebird house is shallower than the others, at 3 1/2 to 5 inches deep. The slotted entrance and shallow depth make these houses undesirable to sparrows and other cavity nesting birds. Slots for ventilation are at the top of the two sides and on the bottom for drainage. This style is popular in Southern states. All other characteristics are common.
  
  

Eastern Bluebird House

• The entrance hole on this house is either round, at 1 1/2 inches across, or a vertical oval at 1 3/8 inches by 2 1/4 inches. One of the sides or the top should be able to open. The inside of the box is roughened with a chisel to help fledglings climb from the nest.
  
  

Mountain Bluebird House

• The only difference between Western and Mountain zone bluebird houses is the size of the entrance hole. The Mountain box entrance hole is 1 9/16 inches across while Western is 1 1/2 inches.