Yes, my idea about the Martin house was not correct – there are two large cavities in this tree which I discovered just a little while ago. I can see this from my property and it is definitely in the vicinity where we see the blues go – the Martin house is probably 40 feet away from this tree but still in close proximity, which is why we thought that was where they were nesting. I believe they (neighbors) do have martin residents, so that is good. This cavity in the tree in very high up so there is no way of knowing if there are eggs or babies, but I will know for sure if my blues start bringing worms over there! Little stinkers …………