Pretty good description of the "bat kerf" in Brian's text. There are a bunch of different bat species with different roosting preferences. For example Big Brown Bat in the northeast likes to roost between the partially separated bark and the trunk on dead standing white ash. I think any bat is going to like getting behind the bark in any species of dead standing tree. Bat's can squeeze into just about any wood crevice or slightly separated bark. Abandoned woodpecker cavities are favored by some bat species. I think you can read Brian's bat recommendations, add some imagination and you're there ;-) The brown creeper (cool bird) builds its nest in the same small space between separating bark and the trunk.
-AJ