Mongolian Gull L.c? mongolicus
December 11th 2003 Choshi Chiba Japan
This bird that was found among thousands of Vega Gulls seems to be a classic adult winter Mongolian Gull. Note the dark-fringed pale iris, sparse head streaking, black-marked dull-toned bill. The facial impression recall autumn michahellis.
Its black-marked primaries are P10-P4.
A Vega Gull L.vegae on the same day for comparison, with a (pale) Slaty-backed Gull.
Note the brighter bill without black marking, wide-spread head streaking (this is a still rather sparse example for vegae), and delayed molt-timing. Molt-timings of Vega Gull show a wide range, and can complete in many individuals in December. But on average, it is obviously later than Mongolian and Slaty-backed Gulls. I sometimes feel the longish tail might be possibly a tendency of Vega Gulls, though naturally it looks variable.