If you put up a bluebird house near an old field, orchard, park, cemetery or golf course, you might have a chance of attracting a pair of bluebirds. They prefer nest boxes on a tree stump or wooden fence post between three and five feet high.
Bluebirds also nest in abandoned woodpecker nest holes.
The most important measurement is the hole diameter. An inch and a half is small enough to deter starlings, which, along with house sparrows, have been known to kill bluebirds, as well as adults sitting on the nest. Bluebirds have problems with other animals too. Discourage cats, snakes, raccoons and chipmunks by mounting the house on a metal pole, or use a metal predator guard on a wood post. The robin is our largest thrush.