Date: 12/11/25 9:28 pm From: Ethan Monk via groups.io <z.querula...> Subject: [EBB-Sightings] Rock Sandpiper and the county line
Hi folks,
As most all are aware, this morning Kevin McKereghan and Tera Freedman found a Rock Sandpiper at the mouth of Cerrito Creek, in the Albany Crescent. While bare part color was suggestive, additional photos of the wingstripe are out and confirm this bird as a Rock, rather than a Purple, Sandpiper. For what it is worth, a number of people have mentioned the underwing color as a diagnostic difference here. I had never heard of this so was intrigued, went home and scrolled through Macaulay for a bit and can now say I observe no difference. But maybe I am missing it.
The bird spent much of its time sleeping, originally very close to the grassy edge where it was hidden unless you were to walk out onto the mud, and then later far out on the mudflats. The mud is shallowest north, as you get into Contra Costa County, so when the tide came up, the bird seemed to go south as the northern mudflats vanished more quickly. The creek mouth of Cerrito Creek is most productive at maybe just under a 3ft tide (there is a station at Pt. Isabel). At about 3 feet the habitat is gone, and all is to the south. In the evening the light is horrible, because you are looking west, so I would target a mid tide (~2-2.5 feet) and not later in the day, if possible, and would look from the creek mouth to maybe a thousand feet south of.
At one point today, the bird was on the creek's north bank, but most of the time was a few hundred yards south. There are no records of this species for Contra Costa, so it would be nice to have a record there! The CalTrans signage, on their website and on the highway seem to show the creek as the county line. This includes the actual markers painted on 580 for the road crews, not just the green signs for the drivers. This has been the traditional belief of birders, too, probably because of these conspicuous signs, but as we all know there is controversy here. The Contra Costa County Assessor's Office maps the county line about 130 feet north of the creek (this varies based on where you measure from, and what the tide is doing) *but *the Alameda County Assessor's Office has their county line about 30 feet north of that! Today at its northmost, a few of us watched the bird maybe thirty feet north of the middle of the creek. So it was not quite there, by the two assessor's offices, but close.
I tried to call CalTrans to figure out where they get their map data from, but I couldn't get to a person at the Oakland office.
