Often called "Buff-bellied Pipit" in Old World literature. This photo was taken through glass so quality is not the best. This was a wet, lost migrant. There was dense fog overnight and this bird landed on our cruise ship the next morning along with 2 Lapland Longspurs, 7 Brambling, a Yellow Wagtail and a Jack Snipe followed us for a while.
The expected race in this area is A. r. japonicus which is much more heavily streaked below and has pink legs. This individual is more lightly streaked and its dark legs eliminate japonicus. I believe this is one of the North American races, either A. r. pacificus or nominate. Brazil speculates that nominate rubescens might wander across the Bering Strait and even winter in the Russian Far East and Japan. I believe this photo supports that idea. There are previous sight records attributed to A. r. pacificus from Okinawa.
Alström & Mild merged pacificus as a junior synonym of nominate. However pacificus is still recognized as valid by Clements/eBird and H&M4 but not by IOC. If recognized, pacificus is supposedly more heavily streaked and yellower (less buff) below. Panasonic DMC-LX5
References:
Alström, P. & Mild, K. (2003) Pipits & Wagtails of Europe, Asia and North America. Identification and Systematics. Christopher Helm, London.
Brazil, M. (1991). The Birds of Japan. Smithsonian Inst. Press.
Brazil, M. (2009). Birds of East Asia. Princeton Univ. Press.
Hendricks, Paul and N. A. Verbeek.(2012).American Pipit (Anthus rubescens), 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/amepip DOI: 10.2173/bna.95
Tyler, S. & Kirwan, G.M. (2017). Buff-bellied Pipit (Anthus rubescens). 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/57806 on 29 June 2017).