Baer's pochard (Aythya baeri) is a diving duck found in eastern Asia. It is a resident bird in North and Central China, formerly bred in southeast Russia and Northeast China, migrating in winter to southern China, Vietnam, Japan, and India. Baer's pochard is a monotypic species. The holotype was collected in middle Amur. It has a distinctive black head and neck with green gloss not present elsewhere in Aythya. But in poor light, it is likely to look completely black. It is very similar and closely related to the ferruginous duck, and they were previously considered to be a single species; Baer's pochard is differentiated by its white flanks when floating on the water, as well as its larger size and longer, more rounded head. Its breeding season varies by latitude and environment. The nest, built from sedges, reeds and other plants, is placed among emergent vegetation, usually in shallow water or on small islands or ridges. Its clutch size ranges from 5 to 14. Males usually take on sentry duty, and females take on the responsibility of incubating. Baer's pochard was once a common species in its range, but is now very rare. The number of mature individuals may be less than 1,000, and its population is still declining. Hunting and habitat loss are considered to be the main reasons. This species has been classified as critically endangered by the IUCN, and listed as a first-class protected animal in China. Taxonomy Baer's pochard was first scientifically described in 1863 as Anas baeri by Gustav Radde in his book Reisen im Süden von Ost-Sibirien. The epithet and English common name commemorate the Baltic German naturalist Karl Ernst von Baer. It is also called eastern white-eye, Siberian white-eye, Baer's white-eye and green-headed pochard. The holotype was collected from a small flock in middle Amur during the breeding season. In 1929, when British ornithologist E. C. Stuart Baker studied the birds of British India, he treated Baer's pochard and ferruginous duck as conspecific. However, Chinese ornithologist Tso-hsin Cheng treated them as two distinct species, as they had breeding grounds which did not overlap, and he had seen no evidence of hybridisation. It was once commonly considered that Baer's pochard may have originated from the eastern population of the ferruginous duck, but American ornithologist Paul Johnsgard proposed it is not supported by the behavior, which suggested Baer's pochard is closer to the hardhead.