One of the nest boxes that Claudia and I cleaned out today, contained four little mice. Probably they are white-footed mice, but deer mice look almost identical. At one point three of them clung to the back of the nest box, peering out after I opened the box to check it. I left the four in their winter nest as no birds showed any interest in this nest box all spring and summer, and it remained empty until autumn when these guys took over.