For a week now, I've been checking the white towel I put on the ground beneath the bathouse. Today I saw guano! I just went outside (7:15 p.m.) and shone the flashlight up into the house to confirm occupation. "My" bat is back! Added to historical data:
First occupation of the season
2010: March 12
2009: March 7
2008: April 12
2007: June 15 (house erected April 12)
I like to note which chambers the bat(s) occupy through the season. As is typical, the bat is now in the chamber closest to the house wall (south-facing brick wall, lots of radiant heat). There are four chambers total. When the weather starts to warm, I've observed the bat(s) shifting to the second or third chamber. My house is large enough to accommodate a nursery colony but it hasn't happened yet. :-( I think what I have every year is a bachelor bat. One year there were two bats for a brief time, but other than that I have Mr. Solo. I'll take what I can get.