There was a rockslide the day before just south of the nest More gulls swallowing those "things", which I learned were sweet potato sea cucumbers (Molpadia arenicola). They're quite slimy.
Did the long walk down to Blacks Beach again. The falcons weren't around at 3p when I started, but they were on the cliffs watching the sunset on my way back. Lots of gulls with sea cucumbers.