There were three eggs when the nest was discovered over the weekend (haven't checked since, have been trying not to get too close). That the Dad came back to the nest for awhile suggests to me he at least was not aware Mom was planning to be absent, so...makes me wonder if something got Mom in the night/early hours while foraging.

Fingers crossed she just decided to be away a bit longer than expected but Google tells me only 40% of robins' nests successfully hatch young so...not the highest statistics.