Tundra Swan

The Tundra Swan is currently considered a subspecies of the Whistling Swan, a Holarctic species whose scientific name is Cygnus columbianus bewickii. It is found in Eurasia. The North American subspecies C. c. columbianus is the nominate subspecies, also known to English speakers as the Tundra Swan. The Whistling Swan is a much smaller species than either Trumpeter or Mute Swans. Here, I will primarily discuss the Tundra Swan.
There is no sexual dimorphism; the male is simply slightly larger. The adult plumage is entirely white. During breeding season, the head and neck are often reddish brown due to feeding on submerged vegetation. The bill, with its concave culmen, is black and yellow. The yellow originates from around the eyes and reaches the nostrils down the upper mandible in an arc. The eye is dark and the legs are black. The birds in the eastern part of the continent have a break in the yellow around the forehead. American birds often have only a single arc of yellow at the lore, with the yellow reaching the black bill slightly more in some individuals.
The juvenile and first winter birds can be readily distinguished by their overall brownish, grayish and rufous plumage, with the head and neck usually being the darkest areas. The bill is pink and black, without yellow at the base. The eye is circled in pale tones and the legs are grayish pink. The bill and legs will darken in the second year, though the yellow of the bill will take longer to develop. Immature birds can still be identified as such throughout their second winter. They will not typically breed until they are three or four years old.