Thought I'd throw in some observations from my swallow houses at my house in Reedsport and office in North Bend. First on the insect thing we had mosquitos like we've never had before earlier. They are much better now especially since my VG nest is close to fledging and the parents are feeding babies all day like crazy. I even saw a first today, she brought a small dragonfly to the nest.
This year I built new houses with the oval holes, seeing if they excluded the House Sparrows. I can say they pretty much do. I have seen hens squeeze in but none made a nest. They gave up. Swallows, both VG and Tree had no issues with the holes. Unfortunately, this year I only and active VG house and one not used but was looked at for a while. On the Tree swallow side of the house both houses were being worked on but those houses and the one I had in North Bend the House sparrows even though they could not use them the males guarded them like I've never seen before. Even though the hen had an active house that she always does across the street from me she was trying to establish a second house but gave up. But every day I would see the Tree's on the lines near the houses but not going in and usually a male sparrow on the roof next door doing his awful chirping and standing guard. The Tree's stuck around for a few weeks but are pretty much gone now.
I have thought about traps for a while now but this year they will become a reality. A Starling trap also. I have seen very high numbers of fledglings of those also. Wish I knew a falconer that could use the birds.