Adult male in front; female in back. Female Eurasian Wigeons are reported to be polymorphic with some individuals having a gray morph in which the head color resembles that of the similar American Wigeon. We spent some time scanning through Eurasian Wigeons looking for Americans, finding only one obvious male. Not only did we fail to find any female American Wigeons, we also failed to find any gray morph female Eurasians. This gray morph seems to be extremely rare in Japan if it exists at all. The three wigeon species, 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 otherwise polyphyletic. Canon PowerShot SX60.
References:
Carboneras, C., Christie, D.A. & Kirwan, G.M. (2019). Eurasian Wigeon (Mareca penelope). 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/52862 on 5 April 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