Mute Swan (Cygnus olor) is one of the biggest species of the order Anseriformes. It is the heaviest modern flying bird. Mute swan is not really "mute"; this name comes from the hissing sounds it produces. The duration of their lives is remarkable - there are reports of species over 50 years of age.
Body length of the Mute Swan is 145-160 cm and wing span of 208-238 cm. Its body weighs between 7 and 15 kg. Between the sexes exists only minor differences. The male is larger and has a swelling at the base of the beak. Plumage is snow white. Beak is orange during the breeding season and red for the rest of the year with a black tip. Feet are black. The young birds are pale grey with brownish tint, they turn white first in the third year at maturity. Mute Swans, especially the male birds have very distinctive silhouette with S-curved neck and slightly lifted wings.
During migration and wintering mute swans can be seen in the whole country. They prefer larger freshwater or brackish ponds with extensive reedbeds and open water area. Along the Black Sea coast the number of wintering birds can reach several hundreds.
Breeding period begins in mid-March. Marital behaviour is a complex ritual of synchronized nodding head, dipping its beak into the water, intertwining necks, standing with the partner against each other, etc. The nest is built by both partners on a small floating island or bent old reed. It lays 5-8 eggs. Incubation lasts around 35 days. The little chicks hatch sufficiently developed to be able to move and feed independently. Their diet consists of aquatic plants, seeds and small creatures inhabiting the aquatic vegetation.
Mute Swan lives in half-wild state as a bird park, and even the wild populations often settle to live near humans. The Mute Swan is protected specie included in the Red Book of Bulgaria.