Welcoming bluebirds to your outdoor space can be as rewarding as watching those new shoots of perennial plants burst forth in early spring. Providing homes made in the correct material, size, and shape will encourage friends with feathers to stay and raise their young where you can watch.
Since most birds nest in trees, the natural material choice for birdhouses is wood. If purchasing a house, avoid metal, glass, plastic or other materials that may get hot in the sun and kill baby birds inside. Pressure treated wood or plywood is not a good choice either, as it may emit dangerous fumes when wet. Simple, untreated wood is the best option if you plant to purchase or make your own bluebird house.
Size and Features
According to University of Maine Cooperative Extension wildlife specialist Catherine A. Elliott, a typical bluebird house should have a 5-by-5-inch square base, 8 to 9 inches deep on the interior with an entrance hole approximately 6 inches up from the base of the house. The entrance hole or "door" for the birdhouse should be 1 3/8 inches in diameter. The roof should be slanted and overhang the house by at least 2 inches to deter cats or other predators from attempting to reach inside. Ventilation holes in the top and drainage holes in the base will keep the birds healthier, and a hinged top allows for seasonal cleaning of the home for next year's use.
Bluebirds, along with tree swallows and great crested flycatchers, love homes that mimic a hollowed-out tree cavity. To re-create this habitat, a small box-shaped home with a frontward slanted roof is ideal. The inclined roof will allow precipitation to run off, as well as protect the top of the home from predators who many try to perch. Because loitering predators like squirrels or cats may be a nuisance, don't add a perch outside the opening to a bluebird house. These adept birds can land on the narrowest of hole openings.
The best finishes to welcome a wild bird are simple and natural. A bluebird may be leery of a brightly colored dwelling, as well as a newly shellacked or oiled one. A simple stain, wood oil or natural based paint finish (such as milk paint) is not only inexpensive but also kinder to winged visitors. Never paint or treat the inside of a birdhouse, as it is both unnecessary and potentially harmful to curious, pecking baby birds.
Bluebirds are especially wary of cats, so the best placement for their dwelling is high and away from heavily treed areas. Ideally, the house should be attached to a metal pole no lower than 6 feet off the ground and 300 feet from any other bluebird house to avoid territorial conflicts, suggests Elliott. Wooden stakes are also acceptable, although cats may be able to climb them. Position the house facing north or east to avoid extreme morning or evening heat.