As a reminder of my points above, and their general applicability outside of my own experience, I subsequently walked north to bird the Ballona Channel wherein I met another birder.
Other birder (chewing on a sandwich): “Did you see it?”
Me: “You mean the Yellow-crowned Night-Heron?”
Other birder (chewing on a sandwich): “Yes.”
Me: “Yep. I just came from there. It was feeding on the southwest shore.”
Other birder (putting away sandwich): “Really? I didn’t see it. Guess I’m heading back over there.”
I never saw him again, and I do not know if he ever saw it, but I do know the bird has been seen daily through today. In some sense, though, I also became that birder (chewing on a sandwich) when it came to the rest of my day. I still do not have Common Tern or Black Skimmer for Los Angeles County for the year. Birders have observed both species recently, repeatedly, at the Ballona Channel. Once again, on yet another visit there, I come up empty. I continued my day a little further inland at the Ballona Freshwater Marsh. My primary goal bird there was a Rose-breasted Grosbeak that had been reported the previous few days in an elderberry above the road on the south side. I spent about a half hour there, by the elderberry, agonizing whether to stay or go. I decided to leave. When I reached the north side of the marsh and my Jeep, I looked back at the elderberry far away and saw some birders looking up at it. I later got an ebird report in my email stating it had been observed in the elderberry at just about that time.