Enjoyed this blog Rob.
A couple of summers ago, I had a nest of tree swallows in one of my boxes...they were busy for a while feeding and then all of a sudden nothing...I figured they had fledged....and then to my delight a week later they were nesting again....and again, they were busy for a while and then silence. When I checked the box, I found the entire clutch dead...but even worse, the second nest was built on top of the first mummified clutch.
