There is truly not much you can do, but watch and pray!
I have seen one deserted just hatched nest. I tried to find help and/or advice, but there was no help for this situation. I let nature take its course rather than killing the babies which would probably have been better for them. I chose that option because if there was even a remote chance of mama bluebird returning in time to save them I didn’t want to interfere.
I never knew what happened to the pair. One theory is that something happened to the female and the male just left. He could not have saved them; only mama can do that at this stage.
Cari
Willamette Valley, Oregon