The swan goose (Anser cygnoides) is a large goose with a natural breeding range in inland Mongolia, Northeast China, and the Russian Far East. It is migratory and winters mainly in central and eastern China. Vagrant birds are encountered in Japan and Korea (where it used to winter in numbers when it was more common), and more rarely in Kazakhstan, Laos, coastal Siberia, Taiwan, Thailand and Uzbekistan.
While uncommon in the wild, this species has been extensively domesticated, when it is known as Chinese goose. The original spelling of "cygnoid." (with a fullstop, suggesting an abbreviation) is widely treated as an orthographic error to be corrected to "cygnoides", but some authors regard cygnoid (without the fullstop) to be the correct original spelling which should be used, citing the comparable case, universally accepted, of the spelling of the name Estrilda astrild. As of early 2025, this dispute over the spelling remains unresolved.
It is now one of 11 species placed in the genus Anser that was described by the French zoologist Mathurin Jacques Brisson in 1760. The species is monotypic, with no subspecies are recognised.
The upperparts are greyish-brown, with thin light fringes to the larger feathers and a maroon hindneck and cap (reaching just below the eye). The remiges are blackish, as are the entire underwing and the white-tipped rectrices, while the upper- and undertail coverts are white. A thin white stripe surrounds the bill base. Apart from darker streaks on the belly and flanks, the underside is pale buff, being especially light on the lower head and foreneck which are sharply delimited against the maroon. In flight, the wings appear dark, with no conspicuous pattern. Uniquely among its genus, the long, heavy bill is completely black; the legs and feet, on the other hand, are orange as in most of its relatives. The eyes' irides are maroon. Juveniles are duller than adult birds, and lack the white bill base and dark streaks on the underside.
Ecology
It inhabits steppe to taiga and mountain valleys near freshwater, grazing on plants such as sedges (Cyperaceae), grasses (Poaceae) and water plants, and rarely swimming. It forms small flocks outside the breeding season. In the winter, it grazes on plains and stubble fields, sometimes far from water. Birds return from the winter quarters around April, and the breeding season starts soon thereafter. It breeds as single pairs or loose groups near marshes and other wetlands, with nesting activity starting about May. The clutch is usually 5–6 but sometimes up to 8 eggs, which are laid in a shallow nest made from plants, placed directly on the ground, often on a small knoll to keep it dry. The precocial young hatch after about 28 days and become sexually mature at 2–3 years of age. Around late August/early September, the birds leave for winter quarters, where they gather in small groups to moult their worn plumage. and upright posture.
Charles Darwin studied goose breeds as part of his work on the theory of evolution. He noted that the external differences between Chinese geese and breeds descended from the Greylag goose belied a rather close relationship:
<blockquote>"The hybrids from the common and Chinese geese (A. cygnoides), species which are so different that they are generally ranked in distinct genera, have often bred in this country with either pure parent, and in one single instance they have bred inter se."</blockquote>
Conservation
The species is currently classified as an endangered species by the IUCN based on ongoing population declines and range losses, exacerbated by recent poor breeding success and unsustainable levels of hunting.