This afternoon I was lucky to find what appears to be another adult Slaty-backed Gull at Ferry Point, with many other observers getting to see the bird. The bird was first seen in the water southeast of the Ferry Point pier near a fishing boat, then flew over to the pond at Miller-Knox where we were able to relocate it loafing with the California and Ring-billed Gulls. We lost track of it when it flew off from the pond back toward where a lot of the feeding activity is. This bird is much more heavily marked on the head and neck than the individual from yesterday (which we did not see).
Photos of the bird are here: http://seagullsteve.blogspot.com/2014/02/another-ferry-point-herring-run-another.html
Thanks to Alvaro Jaramillo, Brian Daniels, Curtis Marantz, Linda (didn't catch your last name, sorry!), Noah Arthur, Dan Singer and David Wimpfheimer for helping work over the bird with me. Gull activity has increased from yesterday, with more Glaucous-wings (and their hybrids) present.