Here are four definitive-alternate Mongolian
Gulls Larus (c?) mongolicus, photographed at Olkhon
Island, Lake Baikal on August 16, 1997 by Geert Groot Koerkamp.
Geert comments: "Impression of most adults was that they
were rather robust, with long yellow bills with red spot on gonys
not extending onto upper mandible and no black. Eyes appeared
dark from a distance, some birds having a particularly beady-eyed
appearance. Closer looks often showed a yellowish iris. Orbital
ring red. Legs mostly pink or greyish. I have studied gulls at
Olkhon Island, in the centre of Lake Baikal, and I haven't seen
any yellow-legged birds there. Tip of P10 not entirely white,
but with a subterminal black band. I haven't seen mongolicus
raise their wings during long call, as described for cachinnans
by Jonsson."
Note the stage of molt apparent here:- the first three birds have
a new P5 and old P6 - P10 , plus old/worn upperparts feathers;
the lowest bird is more advanced, with a new P6 almost fully-grown
and fresh upperpart feathers:
First bird:
Second bird - note how in the upper image there is a small black
mark near the tip of the upper mandible, but is is not visible
in the lower image; is this debris from digging in the dark soil,
or an actual feature of the bill plate? - it seems coincidental
that the next bird (below) has an almost-identical mark, yet Geert
comments that these birds were feeding in a muddy field:
Third bird - note the dark marks near the tip of the tail; is
this a 3rd-alternate molting into 4th-basic?:
Fourth bird - Geert comments that this is a rather small-billed
individual:
