Bluebirds are nesting in our yard. Just as in real estate, location determines desirability. This birdhouse was a gift from my parent-in-laws and has been in our yard for many years. Apparently, I needed to move the birdhouse a few times and wait a couple more years before the bluebirds found the birdhouse acceptable.
A nice feature of this birdhouse is the bottom is not fixed, but is a door that hinges so that it can be opened to clean out the birdhouse. Meanwhile, the bluebird pair is building a fine nest. I am not sure what the male bird has in it beak in the next picture, but it looks like a cocoon of some sort.
The metal ring around the opening was installed to prevent squirrels from enlarging the opening. It is a large washer that two holes were drilled through so it could be secured to the birdhouse with two small screws. I first checked to see what size hole bluebirds prefer before adding the metal ring. Building or buying the right kind of birdhouse is important, but so is the height off the ground. This one is hanging from a garden Shepard’s hook. Here is a website with information on specifications for different species of birds: http://www.wild-bird-watching.com/Building_Bird_Houses.html#sthash.SswIVytc.dpbs