I posted this back in 2007. The advice still stands. By the way, autumn is a great time to put an owl box.
In case you're thinking of putting up an owl box of your own, here's how I did mine.
I put the owl nesting box on a swamp maple tree. The opening, 3 inches round, faces south-ish. The box is roughly 8 to 9 feet off the ground.
The location is well-suited for screechers.
The area is wooded but swampy, with a stream nearby. The box is about 40 yards from my house, and screechers seem to like to live near people.
The box was up for 22 months before the first screech owl moved in -- in October 2004.
After I installed the screech-cam and Mr. Ace had moved in, I met an owl expert who reviewed photos of the site and made several (inexpensive) suggestions to increase the odds of success.
I took all the advice -- after checking the owl-cam monitor to be sure I chose a rare day during the winter when Mr. Ace was roosting elsewhere.
Here's the advice (If you have any more to share, pass it along):
Suggestion: Install aluminum flashing on the tree below the nesting box.
Reason: Flashing makes it harder for raccoons and other varmints them to get into the box.
Suggestion: Remove all rocks and other objects on the ground under the nesting box.
Reason: When owlets leave the nesting box, they invariably fall to the ground; they don't fly. So it makes sense to clear the ground they'll fall on.
At some point I'll put some mulch under the box -- right now the ground is underwater from the recent flooding.
Suggestion: Find a nearby tree with a branch the same height as the nesting box opening, then lean several small branches against the base of that tree.
Reason: Once the owlets fall to the ground, they look for a nearby tree with a branch where they can be fed by Mom and Dad.
Piling the underbrush at the base of the tree makes their task easier. (They do not climb back into the nesting box, or up that same tree.)
Suggestion: If a nearby tree lacks branch at nesting-box level, install one yourself.
Reason: The owlets need to be somewhere near the box opening to be fed.
Young screech owls have a mortality rate of 70 percent, according to one study. I want to do all I can within reason to increase the odds of survival.