3 abandoned nestboxes (1 Viewer)

Hi, I'm new to this forum and hope to get some valuable information from members. We've had several birdhouses up for at least 5 years and have had nesting tree swallows, chickadees and (several years ago) bluebirds. This year, there are nests in 3 birdhouses. Two seemed to be created by chickadees and 1 by tree swallows. All were visited actively for a couple weeks, but I checked today and there are no eggs in any of them. I don't think they laid eggs and already hatched in such a short time. What causes birds to abandon a nest? Is it possible they'll return and then lay eggs?

im wondering the same thing. we've had a couple nestbox here in Oregon that are empty as well. I think it would be possible. but i'm not sure. I sure hope other birds come back and come into the nestbox!