We were pleased to find this adult Amrican Wigeon, a relative rarity in Japan. It was associated with a flock of Eurasian Wigeon. These two wigeon species, the Chiloe Wigeon of South America, the Gadwall and the Falcated Duck have recently been moved from the genus Anas to Mareca. This change was prompted by a genetic study by González et al. (2009) who found that the genus Anas was polyphyletic. American Wigeons are known to hybridize occasionally with Eurasian Wigeons but we saw no evidence of hybridization in this individual. Digiscoped with Panasonic Lumix LX5 | Nikon Fieldscope III | 30X hand-held, no adapter.
References:
Carboneras, C. & Kirwan, G.M. (2019). American Wigeon (Mareca americana). 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/52863 on 21 March 2019).
González, J., H. Düttmann, and M. Wink (2009). Phylogenetic relationships based on two mitochondrial genes and hybridization patterns in Anatidae. Journal of Zoology 279 (3):310-318.
Mini, A. E., E. R. Harrington, E. Rucker, B. D. Dugger, and T. B. Mowbray (2014). American Wigeon (Mareca americana), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.401