Tips for Attracting Bluebirds
By Ken Murray
Provide a well constructed nest box normally from one inch lumber, with the correct size opening, 1 3/16 x 3 1/4 inches for slotted, 1 1/2 inches for round. There should be no perch and it should open easily for monitoring and cleaning, I prefer a side that opens. Place your nest box in a open area of short grass, normally rural, with trees nearby. Trees provide a place where the adults may perch to search for food and will also provide protection for the young, especially during their maiden flight. Avoid brushy and heavily wooded areas because this is habitat of the house wren and they will claim your nest boxes and prevent bluebirds from nesting. Avoid farmsteads and feedlots where house sparrows are always abundant.
Mount your nest box on a smooth round pipe about five feet from the ground to the bottom of the box. Remember to check for underground utilities. If you use a metal T post, place a 2 inch diameter PVC drain pipe, 24 or 30 inches long over it, or other type guard, to prevent predators from climbing it. Never use trees or wooden posts for mounting a nest box. Cats and raccoons can easily climb these and make a meal of your bluebirds. Space nest boxes 300 feet apart, bluebirds are territorial when breeding. In areas where tree swallows compete with bluebirds for nest sites, boxes can be paired 5-15 feet apart. Bluebirds and tree swallows will generally nest side by side.
Monitoring your nest box is very, very important. Check it at least once a week. Adults will not desert their nest or young because of your activities. Record your observations, nest construction, date and number of eggs laid, young hatched and number fledged. Also keep a record of problems you may have encountered. Keep a supply of clean nesting material on hand, you may have to replace a nest with a new one because of dampness, ants or blowflies. Don't open nest boxes after nestlings are 12 days old because they may fledge prematurely. You may want to remove the nest when the young have fledged. Share your records with Indiana Bluebird Society to be complied in their Annual Nesting Report.
Learn to identify other Native Cavity Nesters and allow them to use your nest boxes. Never allow house sparrows to successfully use your boxes (they are not native birds and are not protected by law). Remove their nest and eggs or trap and destroy them. Installing a spooker device on the nest box has also been successful in deterring them from nesting. Remember they will destroy the bluebird eggs and kill adults and nestlings.