*BEST* photos of the three at the above link are the two on the right side that are cropped (the left-most one is to provide a distant perspective and the *GLAUCOUS GULL* in this photo is in the center next to other gull individuals on both sides of it).
(* = Likely the ongoing, previously-reported immature/"sub-adult" (1st cycle/second season or 2nd cycle/3rd season) GLAUCOUS GULL that several people have already posted on eBird and at North Bay Birds.)
As mentioned above, this individual was FAR away and south of the main trail that leads from the Point Blue building west to the Petaluma River. Viewing point was half way on this trail to the river and looking south.
Good to see this bird after again after initially seeing it 3 weeks ago….but missing it on my previous 3/15/23 visit to Shollenberger.....(i.e., It seems to move around in the area...and/or it likes the slightly deeper mud culverts at this location, so disappears from a scope view).
To wit, Noah Arthur and Tony Briggs (who saw the bird after arriving and I showed it to him) agreed with its presence, but we were then UNABLE to again find this individual after I my initial sighting while alone. Hence, I concluded that this Glaucous Gull was foraging in the one of the deeper mud culverts nearby the other ~75 gull individuals: California, Glaucous-winged, Western, and Ring-billed.
(I liked Tony's quip that seeing the bird among the other gulls was so prominent in its light, white color that it appeared suddenly in view "like a white ghost "....:-).....)
Tony, Noah, and other arriving birders may have found this individual again (?) after I left ~6 PM.