...Martin houses, bat houses, etc...
My sister-inlaw gave us a bat house for Christmas this year.
There is a little more to them than I had thought. First, they have to mounted on a building rather than on a tree somewhere, which means that if the bat house becomes populated, you are going to have a substantial pile of bat poop somewhere near a building. Secondly, it can take up to three years to attract bats, and there is no guarantee of success.
I was nearly killed by a bat about 20 years ago.
No it didn't bite me, or anything of that sort. I had noticed something that looked lke bird poop on the side of my house, right under the eaves, and climbed a ladder to investigate. Just as I stuck my face up under the dark eave, I heard a high-pitched squeak, and a bat flew out. In its haste to leave, it hit me right in the nose and I almost fell off the ladder.