Birds from eastern Russia (roughly east of the Taymyr Peninsula) are sometimes separated as the subspecies C. c. jankowskii, but this is not widely accepted as distinct, with most authors including them in C. c. bewickii.

In birds living in waters that contains large amounts of iron ions (e.g. bog lakes), the head and neck plumage acquires a golden or rusty hue.

The eastern birds, apart from being larger, tend towards less yellow on the bill, perhaps indicating that gene flow across Beringia, while marginal, never entirely ceased.

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.

By contrast, the whooper and trumpeter swans' names accurately describe their calls—a deep hooting and a higher-pitched French horn-like honk, respectively.

The winter habitat of both subspecies is grassland and marshland, often near the coast; they like to visit fields after harvest to feed on discarded grains and while on migration may stop over on mountain lakes.

Vagrants on the spring migration have been sighted on Bear Island, Iceland and Svalbard, and in Alaska, Oregon and Saskatchewan in North America.

Birds breeding in western Alaska winter along the Pacific coast from southern Alaska to California; they often move inland – particularly to the rich feeding grounds in the Central Valley – and some cross the Rocky Mountains again and winter as far east as Utah and south to Texas and northern Mexico.

Vagrants have been recorded on the Bermudas, Cuba the Hawaiian Islands, Puerto Rico, and in England, Ireland, Japan, northeastern Siberia and Sweden.

[3][9] 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.

The Arctic fox (Vulpes lagopus), parasitic jaegers (Stercorarius parasiticus), and glaucous gull (Larus hyperboreus) can take the eggs and hatchlings.

[12][13] Brown bear, golden eagles and rarely, gray wolves (Canis lupus) may on occasion succeed at capturing and killing an adult.

The family is sometimes even joined by their offspring from previous breeding seasons while on the wintering grounds; Tundra swans do not reach sexual maturity until 3 or 4 years of age.

Its numbers seem to be slowly declining in the west of its range since the late 19th century, coincident with the expansion of human settlement and habitat conversion in the birds' wintering areas; the eastern whistling swan populations on the other hand seem to be increasing somewhat, and altogether its numbers seem to have slightly risen in the late 20th century (the population was estimated at 146,000 in 1972).

But the main cause of adult mortality is hunting; 4,000 whistling swans are bagged officially each year, while a further 6,000–10,000 are killed by poachers and native subsistence hunter-gatherers.

The tundra swan is not considered threatened by the International Union for Conservation of Nature (IUCN) due to its large range and population.

[1] The proposed subspecies jankowskii was for some time placed on CITES Appendix II; it was eventually removed since it is not generally accepted as valid.

Toxic mining wastes in the Silver Valley, Idaho in the United States has been known to be responsible for the death of migrating tundra swans.