Male and female Tundra Swans make a variety of bugling calls that are smoother and higher pitched than those of the Trumpeter Swan. These include a kuk-kuk contact call between parents and cygnets; a 1- or 2-syllable ou or oh used in flight, when flock members change, or when the flock gathers before dusk to roost; and an oo-ou-oo call, emphasizing the second syllable. This last call tends to be given when members of a pair reunite, after they land, and during or after an encounter with an opponent, as the birds shake their partially extended wings. In aggressive or defensive situations the adults make a hissing sound.
Tundra Swans slap the water with their feet in response to an intruder or when they see or hear other swans in the distance. Air whistling through the wings of a swan in flight can be heard even when the bird is flying 100 feet or more overhead.