Here's something I've noticed,
Any place I've been that has a Dining facility,Chow hall's in the Marine's, College Dining facilities, etc, always a big flock of sea gulls around.
Except when thy serve chicken, then there's not one to be seen, but they are back for the next meal time.
Where I work now I can see the County Jail, (about 100 yards away ) same thing, I don't know the specific menu, but most days there's a flock, then there will be a day when there are none.
I think they know.