Had one of my bluebird boxes returned because all they kept getting was House Sparrows.
So, I cleaned it out and restained the outside;
Today, I installed the box on the edge of our common area using an old red cedar post.
Within minutes a pair of Eastern Bluebirds claimed the box - watched them chase off a pair of Carolina Chickadees and this male House Finch.
I'm convinced that Bluebirds 'stake out' their nesting boxes in the Fall for next Spring's brood(s).