Craig, sounds very much like my situation (see my new post “My blues nesting in neighbor’s tree”) only my blues were here all winter and I am almost sure they are nesting in a next door neighbor’s tree cavity as they have no nest in my yard. Earlier in the season they had claimed one box I thought, as they were at it a lot. But the HOSP came along and I trapped several different males at this box. I have four different boxes, so it is not like there was not an empty box available!