The first-year in the upper photo is Slaty-backed Gull. Note the bulky, short-winged structure and overall uniformity and darkness.
The two closest first-years in the middle and lower photos are neither of them the same bird. The highest bird is heuglini (no pale inner primaries, broad tail band (though not occupying all of tail), while the lower is mongolicus (obvious pale inner primaries, narrow tail band, overall paleness).
GeoffC Author: Paux Time: 1/03/2013 21:45
GeoffC, many thanks for your clear indication of the differences between these 3 birds. This is really a very difficult subject! Author: brendank Time: 3/03/2013 21:29
I think the bird on the right of the Slaty-backed Gull in the top picture could be a Vega Gull. The pale greater coverts, pinkish bill base (which we can't see too clearly), and dark smugging around the eye look OK for Vega Gull. I am not sure whether it is one of the birds in the lower two photos.
Welcome to HKBWS Forum 香港觀鳥會討論區 (http://hkbws.org.hk/BBS/)