Nice you have had success! We have no sparrows hardly at all. Just the stinkin’ wrens, nasty birds.
Which kind of wrens? House wrens, I’m guessing, or Carolina?
It’s interesting how differently we can view the birds. Here wrens are fine. They build their own nests in spots where the bluebirds can’t fit. The holes are a little smaller, I think.
Besides the House Sparrows, our Bluebirds have to deal with food competition from Starlings, and Cowbirds like to lay eggs in Bluebird Cardinal, and Wren nests.
Nature can be very cruel.