I built this birdhouse in October, 2004.  I found the plans on a website.  It is intended to be suitable for Kestrels or Screech Owls.  I placed the birdhouse about 20 feet up in a suitable tree.  Then I sat back to wait for the Kestrels to start moving in.  Amazingly, I saw a Kestrel near the birdhouse within 24 hours of the time I set it up.

Not so amazingly, I have never seen that bird again.  It has been more than a month.