Juvenile Thayer's -like gull, probable Slaty-backed Gull Larus schistisagus
 Choshi Chiba Japan, December 17th 2001
  It looked like Thayer's when I glanced at this bird. but the legs are too long and bill is heavier for Thayer's.
  I feel the countenance  resembles Slaty-backed Gull. This bird is distinctly smaller than other large gulls which 
  were in the surroundings.   a similar bird at Sakawagawa-river on october  22nd 2001
  The right bird is a  1st winter Slaty-Backed Gull.

 
 
 
 
 
 

Wing pattern is OK for
thayer's, and also is OK for 
Slaty-backed.
 The same bird on December 27th
 head and bill shape                                                                     Thayer's Gull, Jan. 6th 2001