My mystery has become a little more confusing and upsetting. I believe house sparrows have taken over the box. They were around maybe ten years ago when a neighbor had horses for a couple of years. During that time I may have addled the eggs. I also installed monofilament line as a deterrent and no damage was done. The HOSPS disappeared when the horses did.
Shortly after I posted here, I saw what I thought was maybe a HOSP on the bluebird box. The next day I removed the empty bluebird nest. Within a day another nest appeared. This nest is made of wider pieces of straw and although not as messy as I remember HOSP nests to be, not as tightly woven as a BB nest. I haven’t seen any HOSPS around. But the nest looks complete. Papa bluebird was sitting on the house briefly but feeling as c fused as I am, I have done nothing to encourage him to stick around.
What I’m wondering is whether the HOSPS could have simply plucked the bluebird babies out of the nest. My only bad experience with them and nestlings involved them pecking the babies to death and starting to build a nest over them. Here no nest building was started until I removed the old nest.
I’ve tried to watch the box but so far have seen nothing going on besides papa BB briefly sitting on the box.
Feeling very confused and eager to get input from others.