That changed back in 2013 when my high school in northern Michigan had a 45 year class reunion. I spent that weekend at a friend's house who lived out in the country on 40 acres and he had a field and valley behind his house. I saw blue birds flying all over the place! At the back of his yard he had a fence post row and each one had a blue bird house on it. I asked him about their occupancy and he said that typically each year half the houses are being used by the blue birds.
As a side note, he called me two days ago and I asked him how the deer population around his house was. He said there's a 10 pointer and a 6 pointer and a few does that he is constantly seeing out in the field.
Then he went into a rant on how the G-damn deer once again destroyed his vegetable garden and the raccoons kept getting his corn.......LOL!
I once asked him why he doesn't shoot the deer from his back deck. Unfortunately Bill had a tough time in Vietnam and he has no desire to shoot a firearm again. So what he does is grant permission to friends to hunt his various properties and they in turn share the venison with him............