cgeoff

Gary,

Should be:

Left: vegae adult
Middel: heuglini 1st year
Right: mongolicus adult

The adult vegae still has fairly extensive, though rather pale, head streaking at this time. Retention of head streaking so late in the winter is characteristic of vegae.

Compare this with the mongolicus on the right, which is shows the classic white-headed mid to late winter appearance of Yellow-legged Gull. I'm sure you'll have noticed that heuglini adults at this time are also, on the whole, significantly whiter on the head than this vegae.

The 1y heuglini shows its slimmer, longer-winged structure compared to vegae and mongolicus. Body moult during the winter means that the underparts are relatively pale, certainly compared to the 1y vegae present over the weekend. The coverts are dark, unlike vegae, and some of the inner greater coverts have been replaced by greyer feathers. Again, this is typical of heuglini, and such moult contrast is not shown by vegae, and only rarely so by mongolicus.

Good photo. Very useful !

Geoff

cgeoff

If you're talking about adult Slaty-backed Gull, the latter is much darker on the upperparts than vegae, darker even than heuglini quite often.

Size does not necessarily stand out as different, as there is some overlap. However, the structure of Slaty-backed is usually quite distinctive, and can be seen on the 1st year birds that occur in HK: stocky, short-winged, relatively thick bill, bulky 'shoulders' and lower neck, thick legs that appear rather short.

Geoff