Swan geese are large and long-necked water birds. They are greyish-brown in color, with thin light fringes to the larger feathers and a maroon hindneck and cap (reaching just below the eye). Apart from darker streaks on the belly and flanks, their underside is pale buff. Uniquely among its genus, the long, heavy bill is completely black in color and a thin white stripe surrounds the bill base; 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.
Swan geese breed in Mongolia, northernmost China, and southeastern Russia. They are migratory and winter mainly in central and eastern China. Vagrant birds are encountered in Japan and Korea (where they used to winter), and more rarely in Kazakhstan, Laos, coastal Siberia, Taiwan, Thailand, and Uzbekistan. These birds inhabit taiga, grasslands, steppes and mountain valleys near freshwater lakes and fast-flowing rivers. In winter, they can be found in marshes, estuaries, plains, and rice-fields.
Swan geese are social birds and form small flocks outside the breeding season. They are crepuscular and forage in the morning and evening. These birds rarely swim and most of their time is spent grazing on plants. Swan geese migrate twice a year; spring migration occurs in late February-early April and the autumn migration starts in August and lasts until mid-September. Prior to autumn migration, the birds usually gather in small groups to molt their worn plumage. The voice of Swan geese is a loud drawn-out and ascending honking "aang". They also produce a similar but more barking honk two or three times in short succession as a warning call.
Swan geese are serially monogamous and form pair-bonds that last only within one breeding season. They return from the winter grounds around April, and the breeding season starts soon thereafter. Swan geese breed as single pairs or loose groups near marshes and other wetlands and start nesting in May. The clutch is usually 5-8 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. Incubation lasts about 28 days done only by a female while the male guards her and the nest. Goslings are precocial; they hatch fully-developed and with eyes open. They fledge 10-11 weeks after hatching and become reproductively mature at 2 to 3 years of age.
Populations of Swan geese are declining due to habitat loss, excessive hunting and (particularly on the Sanjiang Plain in China) egg collecting. In Mongolia, these birds suffer from fires, droughts, and overgrazing.
According to the IUCN Red List, the total Swan goose population size is around 60,000-90,000 individuals. Specific population numbers have been estimated in such areas: in Korea - around 50-1,000 individuals on migration and around 50-1,000 wintering individuals; in Yangtze River wetlands - 87,544 individuals. Overall, currently, Swan geese are classified as Vulnerable (VU) on the IUCN Red List and their numbers today are decreasing.
Due to their grazing habits, Swan geese play an important role in their ecosystem; they provide soil aeration and new habitat for plants which helps new seeds to grow better.
While uncommon in the wild, the Swan goose has been domesticated and introduced and feral populations of its domestic breeds occur in many places outside its natural range. There are two breeds that are direct descendants of the Swan goose: the Chinese goose and the African goose. These breeds have been domesticated since at least the mid-18th century – perhaps even (in China) since around 1000 BC. They vary considerably from their wild parent in appearance, temperament, and ability to produce meat and eggs; the most conspicuous feature is the prominent bill knob and upright posture.