Siamese Robin Nest
Third year in a row a robin (or robinS??) have built a nest on my back porch light fixture. The second year the nest was built to the right of the first and structurally ATTACHED to it. We never removed or even touched the nest even after Mom and babies were long gone. THIS year (just days ago) I spotted a robin building (or RENOVATED??) a third nest INSIDE the first. I haven't actuality SEEN eggs (nest is too high) but she is now happily preparing for the arrival! COULD THIS BE THE SAME ROBIN??? I've read they almost never come back to an old nest and that another bird would not claim "ownership" . ..maybe they're the babies born there all grown up??
This is an interesting observation and an interesting question! Unfortunately, we do not have expertise in bird behavior. An excellent resource on all things about bird biology is the Cornell University Lab of Ornithology. They have research-based information about all types of common birds and perhaps they can answer your questions.