Bewick's Swans weigh 3.4-7.8 kg (7.5-17.2 lb), 6.4 kg (14 lb) on average in males and 5.7 kg (13 lb) in females. They measure 115-140 cm (45-55 in) in overall length; each wing is 46.9-54.8 cm (18.5-21.6 in) long, on average 51.9 cm (20.4 in) in males and 50.4 cm (19.8 in) in females. The tarsus measures 9.2-11.6 cm (3.6-4.6 in) in length, the bill 8.2-10.2 cm (3.2-4.0 in), averaging 9.1 cm (3.6 in). Bewick's Swan is similar in appearance to the parapatric Whooper Swan (C. cygnus), but is smaller, shorter-necked and has a more rounded head shape, with variable bill pattern, but always showing more black than yellow and having a blunt forward edge of the yellow base patch. Whooper Swans have a bill that has more yellow than black and the forward edge of the yellow patch is usually pointed. The bill pattern for every individual Bewick's Swan is unique.


Habitat and Distribution

The breeding range extends across the coastal lowlands of Siberia, from the Kola Peninsula east to the Pacific. They start to arrive on the breeding grounds around mid-May, and leave for winter quarters in Denmark, the Netherlands and the British Isles, Korea, Japan, and southern China around the end of September.


Feeding

In summer, their diet consists mainly of aquatic vegetation - e.g. mannagrass (Glyceria), Potamogeton pondweeds and marine eelgrass (Zostera), acquired by sticking the head underwater or upending while swimming; they also eat some grass growing on dry land. At other times of year, leftover grains and other crops such as potatoes, picked up in open fields after harvest, make up much of their diet.


Breeding

Mate in the late spring, usually after they have returned to the nesting grounds; as usual for swans, they pair monogamously until one partner dies. The nesting season starts at the end of May. The pair build the large mound-shaped nest from plant material at an elevated site near open water. The pen (female) lays and incubates a clutch of 2-7 (usually 3-5) eggs, watching for danger while sitting on the nest. The cob (male) keeps a steady lookout for potential predators. Sometimes the cob will use his wings to run faster and appear larger in order to scare away a predator. The time from laying to hatching is 29-30 days.


Calls and Songs

Have high-pitched honking calls and sound similar to a black goose (Branta). They are particularly vocal when foraging in flocks on their wintering grounds; any conspecific arriving or leaving will elicit a bout of loud excited calling from its fellows.