The ID on photo is best when compared with a standard Heuglin Gull on the same photo, else the degree of pale would be very difficult to assess. I think a lot of present ID is based on the degree on pale on the mantle, which is somewhat variable on Heuglin (depending also on summer and winter plumage as illustrated on a Japanese book). The other major factor is the degree of neck streaking, which is changing in the course of the winter. Light colour of adult seem to be relative stable and so it is relatively useful feature. Last, the pattern on the wing is useful, and so should be given more attention than in the past.
Overall, I think Koel's analysis are sound, although I am inclined to have 1 Yellow-legged on the second set of photo (the bird on the right).
HF Cheung
