Not an expert here but I did hear a speaker at the Michigan Bluebird Soc in March mention that if the bluebirds do that it might be because the original eggs are not viable. On the other hand if another bird chases the originals away it may be building on top of the old nest. I don’t know what the correct action is. I think I would just monitor the nest for a few days and see if it is bluebirds. If so I would probably carefully remove the older eggs. Of course you may be able to identify the species using the nest materials as a guide.
I do remember the speaker talking about putting pairs of boxes a few feet from each other. If the second pair (if that’s your situation) are not bluebirds they may take the other box. I don’t think a second pair of bluebirds will nest in the second box but other species may take it.
Good luck and thanks for sharing. Keep us informed of what happens next.
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This reply was modified 11 months, 1 week ago by
TimC.