Yeah, I figured it was more my fault (I mentioned it in the other thread). Around here the bats tend to "fill" any of bat boxes that the State parks department install (much bigger than mine which I copied from a commercial design) and they tend to install them near the marshes and swampy areas around here. I live about 1200 feet from a swampy conservation area and my property is only one acre with the best local for the box being the back of my shop/garage. I had never considered painting the box black (figured the smell would repel the bats, since they tend to stay away from the boxes till they seem a little run down (which in retrospect may be because the wood turns darker and thus is warmer).  I actually considered making light weight cast concrete boxes, but because the cement I use has epoxy additives (to allow for very thin castings) I figured it might also drive away the bats. I also suspect that the yellow jacket wasps are another reason... around here they are vicious and will make a nest under the brim of your hat if you sit long enough... In warm weather I do weekly inspections of my house and shop and rarely does a week go by where there is not at least one nest in or on a structure (never mind the 3' x 6' x 4" nest we once found in a wall)... so I could easily see the wasps also being a deterrent.

How big is good sized bat box? Mine were about a foot wide, eighteen inches tall and had about two and a half inches between the three chambers... (I say "were" because they fell apart after about 10 years of vacancy and I removed them about two years ago). The state  boxes seem to be about 4 times as large.