House sparrows harrassed the bluebirds that were trying for a second brood in the bluebird box. We had tried a "sparrow spooker" with mylar dangles with some success. But the persistent sparrows got too aggressive. I installed a "monofilament line" spooker on the nestbox, and so far it has kept them away. Theoretically, the monofilament lines are arranged to prevent the ground-feeding sparrows from landing or perching on the roof or front entry area while bluebirds (aerial feeders) can easily navigate among the lines.
I found the instructions and information at
http://www.sialis.org/hosp.htm scroll down to "monofilament".
