Thanks for your reply...
Well, first off, they had only just hatched, so no feathers, but there were no signs of a disturbance, and no, dare I say it, blood, no disturbed nest, no broken or upset branches, no nothing, nothing on the ground below...just an empty nest. Squirrels are pretty light on their feet, and I suspect, but don't know, that they would take young recently-hatched birds.
I saw what I think are the two Robins just this evening, so the next question is, "Will they have another go at making a nest?". I have read that sometimes they will make a second effort or even a second clutch, but in this case, I doubt they will return to the same nest.
Thanks again.
Thanks again,
Gerry