Mongolian gull, L. c? mongolicus in Japan

Jun.11 2005 Keisuke K
amended at Dec. 31 2007

  I have been interested in Mongolian gull (L. cacchinnans? mongolicus, L. vegae mongolicus, or L. mongolicus) for 3 years.
  I could have seen 3-10 individuals of this taxon in Kyushu every winter. Kyushu Island is more southern place than Choshi port where the most important place for Gulls and gullers in Japan. So Mongolian could be seen in Kyushu mostly on from Dec. to Feb., maybe later than Choshi and Korea. 　 Some birds were very difficult to identify from L.h?.‘taimyrensis’ (adult) or Slaty-backed gull L. schistisagus (worn immature). I can’t certainly define what Mongolian gull is. But every feature in this captions I wrote here worked well to identify Mongolian from others.

1. Typical adult(Plate1-5)
Most of them I saw had dull and dark yellow iris, deep red eye rings, long pale pink legs, longish structure and small black mark on bill. White head is important point, but ’taimyrensis’ has also whitish head in winter. Mongolian’s head was whole white, and some individuals have finer and more restricted streaks than ‘taimyrensis’ on hind neck. Moult is quite earlier than usual Vega, or ‘taimyrensis’. When they come up to Nagasaki on December, they have already completed their primary feathers. These pictures are taken at Nagasaki fishing port in Kyushu.

Plate 1.  Adult Mongolian gull Larus. cachinnans?  mongolicus,
Kyushu Japan, 27^th Jan. 2004
Note long primary and streaks on hind neck.

Plate 2.  Adult Mongolian gull Larus. cachinnans?  mongolicus,
(center) Kyushu Japan 22nd Jan. 2005
Head has already moulted to summer plumage, being a ‘snowman’.They seem to moult around head about January. It’s close to Slaty-backed gull. They are eating ice in this picture. Others are Vega gulls.

Plate 3.4..  Adult Mongolian gull Larus. cachinnans?  mongolicus,
(Jumping) Kyushu Japan 19th Feb. 2005
P4 has black mark..

Plate 5.  Adult Mongolian gull Larus. cachinnans?  mongolicus,
(center) Kyushu Japan 19th Feb. 2005
Same individual as Plate 4. This bird’s legs are very thin and black mark on the bill is small as usual Mongolian gull. Note head has already moulted.    

1.      Typical 1^st winter of 5 birds
They look significantly paler than Vega gull. Moult of scapular completes in early December, so that moult boundary was made between scapular and coverts. Tertials pattern was very variable. Sub terminal band of tail is narrower than Vega. Under coverts were quite pale.   

Plate 7. 1^st winter Mongolian gull Larus. cachinnans?  mongolicus, (Left) Ohhori-park in Fukuoka in Jan.12 2005 Note coverts are worn and scapular is quite new. Right bird is Slaty-backed gull.

Plate 8. 1^st winter Mongolian gull Larus. cachinnans?  mongolicus, 10^th Dec. 2003.Nagasaki fishing port

Plate6. Mongolian Gull, L.c?.mongolicus, adult, at Lake Shinji, Shimane pref.

Plate10. 1^st winter Mongolian gull Larus. cachinnans?  mongolicus, Kako river Hyogo pref.