I've been lucky enough to "host" chickadees for the last 6 years. The first year it was a little war between the bluebirds and the chickadees. The bluebirds have always, w/o a single exception, used the back yard nest box. They already had five eggs and incubation had started when the chickadees started nest building in a front yard box. The bluebirds were having "none of that" and constantly harassed them by going in and out of the dee nest box. I was advised to add a 1 1/8 or 1 /14th inch hole reducer to keep the bluebirds OUT and I did and things were fine for both the bluebirds and the dees. I have bluebirds in the back yard right now and the dees have laid their third egg today in the front yard box. So far, the bluebirds are not bothering the dee box but if they do I'll add the reducer again. I agree with Elly, do no disturb that nest. It's possible the dees will return or that they have and you've just missed seeing them. While they do incubate every day it's possible they have not started incubating yet. Most times females do start incubation the day before, day of or day after the last egg is laid but not 100% of the time so it's premature to think they won't return. I would recommend that you add a reducer to keep the bluebirds out of the box. If, after that, the chickadees don't come back for a full week then I'd remove the nest and eggs and the reducer. But, be sure you've had a chance to look at the box for a full hour before assuming it's been abandoned.

Because of the time frame, are you sure any that hatched didn't already fledge? I would count the eggs. It could be that none of them hatched, but maybe some did and fledged? If the eggs were fertile, they should have hatched weeks ago.

I have no idea; very strange indeed. Robins are usually loyal and caring parents. I would stay away; they would feed the baby while building others "nests" I think. Robins sometimes change their minds and build a few nests before egg-laying; not usually while raising young though.

I'm new to this and I'm concerned about my bluebirds. I had a pair of birds nest in one of my houses and had seen them coming and going for days. When doing yardwork last week, I found some feathers on the ground and worry that one of the neighbor cats may've gotten at least one of them. The nest has 4 eggs in it and I haven't seen either of the birds all week. Is this normal? Should I remove the eggs from the nest?