So, the boxes have freshly painted roofs. There were rumours of House Sparrows in the area. House Sparrows are an invasive, unprotected species which will attack and kill nesting native birds. No one wants them around nest boxes. There are many ways of trying to control, or deter them. Some people swear that House Sparrows will stay away from roofs painted blue. It seemed to be a reasonable thing to try, so four of the six roofs were painted before rains moved in. Obviously, the blue does not bother the Tree Swallow pictured here, and that's a good thing!