Sparrow Trap
The only reason the bluebirds and purple martins nested at my place this year is because I got serious about thinning out the swatter house sparrows.
After I saw a male house sparrow kill a female bluebird, I searched for a sparrow trap, in addition to the more direct pellet approach.
I found these:
http://sparrowtraps.net/Purchase_Info.htmI have caught 69 sparrows in 6 weeks. It works great, in case anyone is interested.