When can I use an existing site for a new nest attempt?

Identical nests where the same exact nest site location can be used for multiple attempts include:

• nests in the same nest box, and the nest box hasn’t been moved or adjusted
• nests in the same fork of the same tree branch
• nests in the same clump of grass (where a “clump” is something with a diameter of not more than 6″)
• nests in different next boxes, when one box is replaced on the same pole by a different style box of the same approximate size
• A second nest built on top of the first by the same species
• A second nest built on top of the first by a different species