The only circumpolar member of the Aythyini tribe, this is a winter male. Two subspecies are usually recognized. However the name of birds in East Asia is disputed with most sources applying the name A. m. nearctica to them. However Banks (1986) found East Asian birds indistinguishable from nominate A. m. marila from Europe in which males are more finely marked above. The name A. m. mariloides previously applied to East Asian populations is invalid. Canon SX60 HS PowerShot.
References:
Banks, R.C. (1986). "Subspecies of the Greater Scaup and their names" Wilson Bulletin. 98 (3): 433–444.
Carboneras, C. & Kirwan, G.M. (2018). Greater Scaup (Aythya marila). 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 https://www.hbw.com/node/52912 on 2 October 2018).
Kessel, B., D. A. Rocque, and J. S. Barclay (2002). Greater Scaup (Aythya marila), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.650
Madge, S. & Burn, H. (1988) Waterfowl. An identification guide to the ducks, geese and swans of the world. Houghton Mufflin, Boston.
Todd, F. (1979). Waterfowl. Ducks, Geese & Swans of the World. Sea World, San Diego.