Nestbox! Take a look at these sneaky little Downy Woodpeckers.
I caught this family of woodpeckers trying to enlarge the hole on this bluebird box a few days ago. It's about 30 feet from my office window and I can watch them while net surfing. The one on the box spent about 30 minutes working on the hole while the others (there was a fourth) worked the tree trunk looking for bugs. They haven't been back to the box since, but we've had them at the feeders.
We've had some bad luck with the boxes this year. Last year we had two boxes and had a swallow family in one and bluebirds in the other. This spring we had both swallows and bluebirds checking them out (plus a third box we added this year), but alas, no birds nested.