I apologize for not posting this sooner, but sometimes I forget what I know! I bet someone out there can relate! The PA Bluebird Society prez, Dean Rust, uses plexiglass skylights in houses as a highly effective sparrow deterrent. Here’s a video where he shows how to do it: https://www.youtube.com/watch?v=XxYDkEe5avM
Read the video comments—lots of encouraging words there. Dean Rust shares this: “I took over a 20 box trail at Hempfield High School in 2012 that was completely infested with Sparrows due to lack of monitoring. After reading an article in Birds and Blooms that suggested letting light into the boxes to deter sparrows, I started drilling 2 1/2″ holes in the tops of the boxes and then covering them over with plexiglass to keep the water out. Within the first year the 15 boxes that I put skylights in were sparrow free, but the remaining 5 boxes had sparrows in them. So I decided to complete the trail so all 20 boxes had skylights. After doing that, the trail was completely sparrow free. To this day (5-5-15) the trail is completely sparrow free!”
Here’s the article that explains the how-to, has materials list: http://www.bluebirdconservation.com/2013/03/discourage-house-sparrows-by-adding-a-skylight/
For those with sparrow issues, give this a try. It could be the solution you need!