Baer's pochard (Aythya baeri) is a diving duck found in eastern Asia. It is a bird in North and Central China, and 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. While in poor light, it is likely to look completely black. It is 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 longer, more rounded head and larger size.

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 fewer 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. 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. 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 .

Baer's pochard is usually a quieter duck, but during its courtship display, both sexes give harsh graaaak. Females may give kura kura kura and males may give kuro kuro at other times.

The species has become extremely rare in its traditional breeding areas, and since 2010, there have been no confirmed breeding reports in all sites north of Beijing. However, the numbers recorded during the breeding season are smaller than those recorded in winter, so there may still be unknown breeding sites. For example, there are some doubtful breeding reports in the Chinese part of Lake Khanka, the Russian part of Lake Khasan, and the . Since 2012, new breeding sites have been discovered in several provinces of China, including Hebei, Hubei and Jiangxi; the latter two cities are far from traditional breeding sites in the Amur and Ussuri basins.

Behaviour and ecology

Baer's pochard is a shy species, that inhabit open, slow-flowing lakes, swamps and ponds. It breeds around lakes with rich aquatic vegetation, nesting in dense grass, flooded tussock meadows, or flooded shrubby meadows. In winter, it forms large flocks on large and open freshwater lakes and reservoirs with other pochards. It has strong wings, and can flyor walk at high speeds. It is also good at diving and swimming, and can quickly take off from the water when threatened or disturbed. In migrating season, they form small groups of more than 10 or dozens of birds, flying at low altitudes in wedge-shaped formations.

Breeding

Baer's pochard appears to have a monogamous mating system, at least within a breeding season. Females leave the nest to forage 2–3 times a day, usually during 6:00-20:00, and lasted for 27–240 min. They cover the eggs with nest materials during forging, and place them onto their back when coming back. If water levels are elevated by heavy rainfall or human activity, females increase the height of the nest to avoid flooding. During the hottest days, females often stand on the nest and shelter eggs from the strong sunlight, whilst allowing circulation of air around them. Females also take water into their plumage and use it to cool the eggs. The incubation lasted for 23–26 days.

Studies have shown that the nest survival rate of Baer's pochards is about 14–45%, and each clutch may lose one to nine eggs. About 20-30% of eggs hatched successfully, and 3–16 young fledged per nest. There are three major reasons contributing to the failure, including nest desertion (abandoned by parents), nest predation (mainly by Siberian Weasels) and flooding. The proportion of these causes varies among years. In Wuhan, Baer's pochard shares breeding sites with cotton teal, eastern spot-billed duck and mallard. Interspecific brood parasitism was not observed. Ferruginous duck was observed displaying to Baer's pochards several times in China and South Korea. Some individuals showed mixed characteristics of common, ferruginous and Baer's pochards, so they may be currently hybridising in the wild. The Baer's pochard has declined sharply in recent years, but the ferruginous and common pochard has expanded their breeding grounds, and even to the core areas of Baer's pochard's, which makes the hypothesis possible.

The research on its gut microbiota showed that the richest microorganism phyla of Baer's pochard are Bacillota, Pseudomonadota and Bacteroidota<!-- called "Firmicutes, Proteobacteria and Bacteroidetes" in the paper -->, which were consistent with those of the domestic goose, duck and chicken. The gut microbiota in diarrheic Baer's pochard is low in diversity, and the species were also significantly different from healthy individuals. Most species in reduced numbers are thought to be intestinal beneficial bacteria.

Threats and protection

Baer's pochard was once a common species in its range, but is now very rare. Baer's pochard was listed as a first-class protected animal in China by 2021. In 2022, media reports state that the first captive population in China was established in the Beijing Zoo, with totally 54 individuals. It is planned to be further expanded and used for reintroduction.

A study published in 2022 showed that most breeding sites (81.8%) and suitable habitats (94%) are not located in protected areas, and overlap with large cities. Current protected areas may be less effective for the conservation under predicted global climate change, closely coordinated cross-border cooperation would be critical for Baer's pochard.

Explanatory footnotes

References

  • Baer's pochard (Aythya baeri) at ARKive