I built these birdhouses a few years ago and have had mixed success. We’ve had birds poke around and a few have attempted to build nests. Squirrels have gnawed away at one of the openings:
I recently took them all down to refinish the wood and add protection around the hole openings. I used metal grommets from an old set of curtains (now using as paint drop cloths):
I am going to experiment with mounting heights to see if that will have an effect on bird occupancy.