Rare visitor from Asia. This adult shows typical dusky winter head markings, with "mascara" around the pale eye and slim bill with pale base typical of Slaty-backed. The broad white tertial and secondary crescents and large white apical spots on the primaries are also good characters. In direct comparison with Western Gulls, the mantle appeared slightly darker. This individual also shows the pot-bellied appearance typical of Slaty-backed, and the spread primaries hint at a "string-of-pearls" which was visible in flight.
Presumably same adult found by Noah Arthur and Don Pendleton at Princeton Harbor on 25 February 2017; and then seen this morning (2 March 2017) at Pilarcitos Creek by several observers. Our observations were late afternoon 4:30-5:30pm.
Digiscoped with Panasonic DMC-LX5 | Nikon FS 3 | 30XWA | hand-held, no adapter.