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. While 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. While the species was long thought to have arisen from eastern populations of the ferruginous duck, American ornithologist Paul Johnsgard says its behaviors suggest it may instead be more closely related to the hardhead.
American ornithologist Bradley Curtis Livezey published a phylogenetic study based on morphological data in 1996, in which he proposed his view on the relationship among Tribe Aythyini. Baer's pochard, ferruginous duck, hardhead and Madagascar pochard are classified in subgenus Nyroca (the "white-eyes"), intrasubgenus relationship is unclear, but the ferruginous duck was suggested to be the sister group of Baer's pochard. The subgenus Aythya (the "scapu", including New Zealand Scaup, ring-necked duck, tufted duck, greater scaup and lesser scaup) is the sister group of subgenus Nyroca. The subgenus Aristonetta (the "redheads", including the common pochard, canvasback and redhead) is the sister group of all other pochards. Two molecular phylogenetic studies on Anseriformes or Anatidae were published in 2000s, some mitochondrial genes were sequenced, but Baer's pochard was absent in both of them.
The mitochondrial genome of Baer's pochard was sequenced and published in 2021. Molecular phylogenetic studies determined the relationships among Baer's pochard and other closely related species:
Description
The Baer's pochard is long with a wingspan. The male is slightly larger, weighing on average , wings lengthed , tail at , and culmen at . Relatively, the female weighing on average , wings lengthed , tail at , and culmen at . Both male and female's tarsometatarsus lengthed .
Breeding male has a black head and neck with green gloss, white or paler yellow eyes, blackish-brown back, dark chestnut breast, white or light chestnut flanks and a short and low tail. The green gloss on its head is unique among Aythya. While it is likely to look completely black in poor light. Female has a dark brown head and neck that blend into the chestnut-brown breast and flanks. Eclipse and first-winter male resembles female, but retain the white eyes, while female has brown eyes. Both male and female have wide white speculum feathers, white vent-side, dark-grey bill, black nail and dark-grey tarsometatarsus.