In the birds l examined in the hand, the iris was dull yellow (very pale, almost whitish, in some), usually peppered with grey (pale bluish-grey to dark grey-brown) minute spots in variable density over a much variable extent of the iris surface. In some birds, the grey was peppered quite uniformly over the iris, often with a few small aggregations forming dark marks on the overall pale eye. In other cases, dense grey spots formed one or more large dark areas over the eye while sparse spotting left the yellow iris colour showing over the rest of it (figure 2). Eye darkness is not sex related. Pale eyes and dark eyes are found in both males and females and pairing occurs irrespective of the iris colour (of eight pairs, the male had darker eyes than the female in four cases and the female had darker eyes than the male in three cases; the partners of the remaining pair showed similarly coloured eyes).

Such a high variability of iris pigmentation makes it difficult to accurately comment on the eye colour of mongolicus. In a first analysis of 43 birds in the hand, l classified 28% of them as pale eyed, 42% as intermediate and 30% as dark eyed. A more detailed analysis, including two more samples (table 3), showed that nearly one-third was pale eyed while grey spots covered more than half of the iris surface in another third. Really dark-eyed birds, however, accounted for less than 10%.

In the field, colour assessment is less easy. Of 236 adult birds studied through binoculars or telescope, 89% were classified as yellow or yellowish eyed. It thus seems that eyes classified as pale grey in the hand are perceived as yellowish in the field while dark-eyed birds accounted for only 4% in the field sample (not statistically different from the 8% found during the in-hand examination).

Leg colour

Pyzhianov & Tupitchyn (1992) described the high degree of variability of the leg colour at Lake Baikal and in Mongolia. They examined various series of birds in the hand, comparing the leg colour with colour charts. Grey legs accounted for 22-40%, yellow 13-27%, pink 21-46% and flesh 4-10%, while 6-30% of the birds showed mix-coloured legs. The proportion of each colour type varied between colonies and from one year to the other in a given colony. Also, in a proportion of birds, the leg colour showed temporal changes. According to Pyzhjanov (1998), not only the intensity but also the tone of the coloration changes, He hypothesized that these changes are related to external conditions (food composition) and age. It is a largely acknowledged fact that carotine-rich food can enhance the expression of the carotinoid colouring matter in the legs of gulls (cf Lonnberg 1933). Any relation with age, however, remains to be proven.

I examined in the hand the legs and feet of 152 birds of most colonies I visited at Lake Baikal. It readily appeared that the fleshy-pink colour usually was tinged with some yellow pigment over a very variable extent, Yellow was more often found on and around the knee and on the rear leg while webs often were of a deeper pink (one pink-legged bird with orange webs was most unusual). Some birds exhibited either bright pink or yellow (pale to bright, then resembling michahellis) legs but most showed a variable leg colour. This rendered any reference to colour charts rather subjective and I relied on my own assessment when establishing the dominant leg colour in the examined adult birds. Of them, 15.8% had flesh-to-pink legs, 76.3% yellowish-flesh, 5.9% pale yellow and 2% bright yellow.

In the field, the perception of the yellow tinge varies markedly, depending on the light incidence and on whether the legs are wet or not (yellow shows better on wet legs). Even birds which seem to have yellow legs when looked at them with the naked eye occasionally showed pinkish legs through binoculars. The field score nevertheless matched the in-hand results, with almost all 555 birds studied in the field showing ’pale’ (ie, flesh or pink more or less obviously admixed with yellow) legs and only seven (1.3%) yellow legs.

Mongolicus 2CY, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Halfway complete moult, P6-P10 still old juvenile. Central MC just replaced, central GC missing, exposing the old secondary bases underneath. New scaps are grey.	Mongolicus 2CY, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Halfway complete moult, P6-P10 still old juvenile. Row of MC just replaced, GC very worn. New scaps boldly barred.
Mongolicus adult, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Full band on P10, small mirror on P9 and full band on P5. Most birds have pale iris and pink legs.	Mongolicus adult, June 01 2013, Bulgan Plantation, Dornod, Mongolia (Hadoram Shirihai). Full band on P10, small mirror on P9 and full band on P5 and black on outerweb P4. Most birds have pale iris with limited peppering and pink legs. Complete moult: P1/P3. PMS=3.
Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai).	Mongolicus adult, July 13 2012, NE Mongolia (Paul Jones).
Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai). Medium mirror on P10, full sub-terminal band on P10 and medium pale tongue on P10. Only tiny mirror on P9, full band om P5 and black on outerweb of P4. Yellow iris with some speckling, red orbital ring.	Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai). Medium mirror on P10, full sub-terminal band on P10 and medium pale tongue on P1. Smal mirror on P9, full band om P5 and black on outerweb of P4. Whitish yellow iris with some speckling (peppering category: 10-25%).

END OF PART 3

CONTINUE PART 4: DISCUSSION