I keep two boxes up. For several years, we would get bluebirds in one of the boxes and tree swallows in the other. That worked well until a neighbor put up a big 8 hole bird condo that house sparrows took over. The house sparrows quickly drove the bluebirds away.
Last year I got pissed and declared war on the sparrows. I bought a trap and caught over 40 of those suckers. A pair of bluebirds did manage to raise a brood last year. This year I've got bluebirds in one box and sparrows in the other. I've been baiting my trap site but don't have the trap out yet. Soon.
