I have a bird house in my back yard that tree swallows (I believe the same pair) have successfully nested in the last 3 years. They came again this year, happy to be here, and did their usual routine. Hung around the yard lots, drove off any other swallows that may have been interested in the house and then slowly started building their nest. They laid their eggs, continued their flying around, monitoring their house and so on. But never really sitting on the eggs. Then about a week ago, we had really cool, wet weather and I wouldn't see them for days. Then they showed up and the female seemed really interested in the chickadee house that I have not too far from the swallow house. The hole is too small for swallows. They have tried for years to get into that house but the hole is just a little too small. Well, one day I look and a swallow is actually in the chickadee house and the resident pair is really upset with this intruder. They continually fly at the hole and try to entice the swallow out. I was worried that the swallow forced herself in and couldn't get out so I went to open the side door but the swallow managed to squeeze herself out. Then a few days later, the female of the resident pair (I think anyway) managed to fit herself into the chickadee house and started building a nest in it. I became concerned that she would nest in it and there is no way the male could fit in through the hole so I plugged the hole. The pair hung around for a day or so and then I didn't see them for days. Today is a warmer, sunny day and they have been back, cruising through the yard, checking out the swallow house (not going in) and checking out the chickadee house again (I unplugged it). I'm wondering if for some reason they have abandoned their first house even though I know there are eggs in it and there are no predators around and nothing to bother the nest. This is the strangest behavior. They have successfully fledged 4 babies each year in their house but it's as if they have deserted it. Could the cool weather have something to do with it? If it is too cool and wet, will they refuse to incubate their eggs? Last year the babies fleded the second week in July so they should have been hatched by now but they haven't really been sitting on the nest at all. Previously, they would go in alot and come out again, but not really spending a lot of time on the nest. Anyone have any suggestions as to what might be going on. I'm almost tempted to enlarge the hole of the chickadee house so they could nest in the box if they really want to.