Despite its widespread Palearctic distribution and large population, this species is now classified as "vulnerable" by IUCN because of recent steep declines throughout its extensive range. Loss of breeding habitat in Eastern Europe along with eutrophication of nesting habitat from agricultural runoff seem to be the major threats. Nevertheless this diving duck was quite common to abundant in a variety of habitats on our winter visit to Japan. Canon PowerShot SX60.
References:
BirdLife International 2017. Aythya ferina (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2017: e.T22680358A110610804. http://dx.doi.org/10.2305/IUCN.UK.2017-1.RLTS.T22680358A110610804.en. Downloaded on 22 May 2019.
Carboneras, C., Kirwan, G.M. & Sharpe, C.J. (2019). Common Pochard (Aythya ferina). 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/52903 on 22 May 2019).
Fox, A. D.; Caizergues, A.; Banik, M. V.; Devos, K.; Dvorak, M.; Ellermaa, M.; Folliot, B.; Green, A. J.; Grüneberg, C.; Guillemain, M.; Håland, A.; Hornman, M.; Keller, V.; Koshelev, A. I.; Kostiushyn, V. A.; Kozulin, A.; Lawicki, L.; L.uigujõe, L.; Müller, C.; Musil, P.; Musilová, Z.; Nilsson, L.; Mischenko, A.; Pöysä, H.; Šciban, M.; Sjenicic, J.; Stipniece, A.; Švažas, S.; Wahl, J. 2016. Recent changes in the abundance of Common Pochard Aythya ferina breeding in Europe. Wildfowl 66: 22-40. Available at: https://wildfowl.wwt.org.uk/index.php/wildfowl/article/view/2638/1758. Date accessed: 22 May. 2019.