This species is a winter visitor in Japan, normally absent after early May, but a few immature stragglers were still present. Often dubbed Common Gull, this is a first cycle (2Y) bird. This race is sometimes treated as a separate species called Kamchatka Gull. It is larger than other races and has a thicker more parallel sided bill as seen in this image. This subspecies breeding in the Russian Far East should be spelled L. c. camtschatchensis based on Mlíkovský (2012) who pointed out that the earlier spelling was a nomen nudem (name without a description) and that camtschatchensis (Bruch, 1855) has priority over kamtschatschensis (Bonaparte, 1857). HBW has made this correction, but Clement/eBird, IOC and H&M4 have not. Canon PowerShot SX60 HS.
References:
Burger, J., Gochfeld, M., Kirwan, G.M., Christie, D.A. & Garcia, E.F.J. (2017). Mew Gull (Larus canus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/53970 on 16 June 2017).
Howell, S.N.G. & Dunn, J.L. (2007) Gulls of the Americas. Houghton Mifflin, Boston.
Malling Olsen, K. & Larsson, H. (2003) Gulls of Europe, Asia and North America. Christopher Helm, London.
Mlíkovský, J. (2012) Nomenclatural notes on the East Asian form of the Mew Gull Larus canus Linnaeus, 1758 (Aves: Laridae). Zootaxa 3356: 65–68.
Moskoff, William and Louis R. Bevier. (2002). Mew Gull (Larus canus), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/mewgul.