Saturday morning (7:30-9:00) I did a sea watch from the south end of the Great Highway. Winds were out of the E-SE, seas were relatively flat, skies were overcast, and visibility was very good.
Shortly after 8 AM, I noticed a whale blow out towards the horizon (likely Gray Whale), and a bit of a frenzy of gulls and cormorants around that. While I was scoping that activity, a group of 3 birds crossing in the foreground a few hundred yards out caught my eye. I watched them flying above and below the horizon and plunge-diving for several minutes as they steadily moved south. They were obvious terns, on the large end of the spectrum of terns, long-winged but not broad-winged, with pale gray upperparts and mostly white underwings, with just a hint of dark under the outer primaries. Their longish tails had a shallow fork. There was a small amount of black on the rear of their heads and their bills were thick and stout and appeared orangish, not red. The wings were not as broad as Caspian Terns and they did not show the significant amount of black under the primaries that Caspians show. Neither Royal nor Elegant Terns are expected in Northern California at this time of year and Elegant Terns have been gone from SF waters since early December. Having observed thousands of Elegants from SF seawatches in the summer and fall, these 3 terns appeared to me as thicker- and stouter-billed than the longer-billed Elegants and also a bit bulkier and heavier fliers. I last observed the 3 ROYAL TERNS heading south off of Ft. Funston. I can only speculate that they continued into San Mateo County.
Other observations of local interest during the sea watch:
BRANT 2 (flying N)
Surf Scoter 180+
Black Scoter 1 m.,1 f.
Red-br. Merganser 1 f. (flying N)
Com. Loon 2
Pacific Loon 1
Red-thr. Loon 420+ (most flying N)
Brown Pelican 60+
Marbled Godwit 57
Heermann's Gull 260+
Com. Murre 6
Also: Harbor Porpoise 2
A brief stop at the concrete bridge with Hugh Cotter produced some nice 1W gulls for that location: 1 Bonaparte's, 3 Thayer's, and 1 Heermann's.
We then headed over to the Bay-side to check out the current herring run. Off of India Basin Open Space there were hundreds of ducks -- mostly Greater Scaup, Ruddy Ducks, Bufflehead, Am. Wigeon, and Surf Scoters -- within which we also observed 12-15 LESSER SCAUP, 1 f. GREEN-WINGED TEAL, 1 f. Com. Goldeneye, and a striking-looking male Am. Wigeon with an all-cream-colored face. There were a lot of gulls along the shore, including good numbers of Herring and Thayer's, 4 Forster's Terns, and typical winter shorebirds including at least 9 Black-necked Stilts and 1 Spotted Sandpiper.
We finished up at Agua Vista where we (and other birders further up the road) pored through hundreds of gulls, including many Herring and Thayer's and 5 or so Heermann's, and various apparent hybrids, as well as 20+ Brandt's Cormorants (good for the Bay-side). We did not find any rare gull species among the hordes of gulls during our short visit.