1. This appears to be adult mongolicus. Upperparts are rather pale, head has faint and sparse streaking only, base of underside to p10 is whitish and contrasts well with distal part of feather, the bill tip appears to have a very pale tip and the primaries are somewhat worn. Leg colour fits also, though rather more greyish than usual.
2. Left hand bird has combination of pale upperparts and retarded moult (p8 not quite full grown) that together indicate hybrid heuglini x vegae (i.e. taimyrensis). The iris is pale and has little dark flecking, imparting a very heuglini appearance. I think the difference in darkness of mantle grey is exaggerated by the slightly different angles these two are standing at. The right hand bird seems to be pretty good for vegae, though without seeing the primary moult, it is difficult to be sure.
3. Structurally this bird feels like heuglini, and the extension of red onto the upper mandible favours taimyrensis. However, primary moult is pretty advanced, with p9 nearly full grown as far as I can see, though I'm not sure what's happening with p10. It appears to be about half grown on the underside of the far wing, but I can't see the tip. Legs are pink. Overall I would say this is a taimyrensis at the vegae end of the spectrum.
4. This is presumably also a hybrid, with the creamy-pink legs indicating vegae genes, while the very pale iris, retarded moult (p8 just complete) and dark upperparts reflect heuglini influence.
Strictly speaking, and following the argument of Yesou in particular, large gulls wintering in HK are hybrids, as taimyrensis is a hybrid of vegae and heuglini. Whether we get pure heuglini here is open to debate (I personally have not yet seen anything convincing), though we do get a core of birds of fairly consistent appearance. The birds that stand out as hybrids here are those closer to vegae, while the birds that stand out as hybrids in Japan are closer to the taimyrensis we get here.
Finally, it's great to see these photos and be able to comment on them. Those of you who photograph gulls, please do try to shoot a selection of birds, adults and immatures, each time you go. I would very much like to use your shots as a reference in the future.
Geoff
[ Last edited by cgeoff at 6/02/2010 10:07 ]
