The Mute Swan (Cygnus olor) became the national bird of Denmark in 1984, replacing the Skylark (Alauda arvensis). At first the Mute Swan was not granted officially status as the national bird of Denmark by law but by a popular vote held by a Danish TV show.
No trumpets but vibrant throbbing of the wings.
The Mute Swan is not completely mute. It is less vocal than the noisy whooper and Bewick’s swans which communicate in the air emitting strong trumpets. However, mute swans do make a variety of grunting, hoarse whistling, and snorting noises, especially in communicating with their cygnets, and usually hiss at competitors or intruders trying to enter their territory. The most familiar sound associated with mute swan is the vibrant throbbing of the wings in flight which is unique to the species. The mute swan is one of the heaviest flying birds.
“The Ugly Duckling”
The Mute Swan probably derives its popularity in Denmark because of its role in “The Ugly Duckling” by the Danish poet and author Hans Christian Andersen (1805–1875).
The Mute Swan is native to Denmark. The nest is build near water, or on floating islands. As material they use herbs and branches of small thickness. The structure can have a diameter of two meters.
Sources: worldatlas.com, 10000birds.com, wikipedia, nationalpedia.com.