When we move here we put up a Bluebird box. Almost immediately we had Bluebirds, which nested twice a year in our box. This went on for five years, then on the sixth year a House Wren moved in before the Bluebirds, for just that year. Since then no Bluebirds will nest there. The male Bluebirds comes all the time to inspect the box, goes inside for a while, then comes out and flies away. This goes on all day. I have changed the box, but he still does the same thing. What's happening now? Any suggestions would be helpful.