Choshi is one of the biggest wintering site for Vega Gull in the world. However, it is difficult to find some Mongolian Gulls among the huge gull flock, beyond our expectations (though the difficulties of identifications might be disturbing us). And I occasionally feel Thayer's Gulls might be rather regular here than Mongolian Gulls!

But, on March 5th 2004, a larger number of  white/whitish-headed individuals was unusually found. (Vega Gulls have strong tendency to remain winter plumage even in mid-March)  And interestingly more than 90% of  white/whitish-headed individuals that I suspected to be Mongolian Gull (over 10 individuals) had 7 black-marked primaries (P10-P4).

Although I have to say identifications for adult Mongolian Gulls in the wintering range are not easy and do not always have 100% reliability, so far I personally think most of them must be Mongolian Gull.

<< Click thumbnails in the left frame to browse each individual.

Vega Gulls on March 10th 2001, for reference.