Mute Swan
Cygnus olor (Gmelin, 1789)
Cygnus olor Temm.: Elwes, Buckley, 1870: 338; Radakoff, 1879: 175; Cygnus olor (Gm.): Reiser, 1894: 179; Klain, 1909: 143.
Order Anseriformes
Family Anatidae
Conservation status: in Bulgaria: Vulnerable VU [D1]; International: BeC-III, BoC-II, BD-II/2.
General distribution. A Palearctic species breeding in Europe, Kazakhstan, Asia Minor and Central Asia, Iran, and China. It winters near the North Sea and the Baltic Sea, in Central and Southeastern Europe, Central Asia, the Persian Gulf, the Yellow Sea. A partial migrant.
Distribution and abundance in Bulgaria. A resident, passage migrant and winter visitor. It breeds along the Danube and the Black Sea coast. There are isolated breeding places within the country. The pairs in Bulgaria are estimated at 12-36, which shows a certain growth in comparison with the population in 1985 (5-20 pairs) [1]. Certain breeding has been recorded in over 25 UTM (10x10 km) squares, but with a low density: from one to several pairs in every habitat [2]. In the winter, it is mainly found along the Black Sea coast, where in the 1997-2001 period from 193 to 4 039 birds wintered, with average numbers of 1 377 individuals [3, 4, 5].
Habitats. Permanent freshwater, brackish or salty lakes, marshes and water basins, shore freshwater, brackish or salty lagoons, the shelf zone of the Black Sea coast.
Biology. It starts breeding in the middle of March [6]. It breeds in separate pairs [7]. The nest is on a small floating island [8] or lying old reed. It is built out of water-loving vegetation; a diameter of up to 1,2-2 m and a height of up to 50 cm. It lays 4 (5) to 8 (9) eggs, incubating for about 36 (35-41) days [9]. About 4 ½ months after hatching, the young ones are already on the wing. Sexual maturity is reached at the age of 3-4 years. It feeds on water plants, seeds and small invertebrate animals with them [9]. During the winter it also feeds in sown fields.
Similar species. The Whooper Swan (Cygnus cygnus) and the Whistling Swan (Cygnus columbianus).
Negative factors. Poisoning by lead pellets or fishing weights; illegal shooting; disturbance; loss and degradation of habitats.
Conservation measures taken. Protected according to the Biological Diversity Act. Included in the Red Data Book of Bulgaria (1985). The major breeding places and wintering sites are specified, some are declared Protected Sites, and for some of them Management Plans are enforced.
Conservation measures needed. Placing all key breeding sites under protection. Active enforcement of Management Plans and preparation of such plans for other significant sites. Restoration of dried up wetlands and rehabilitation of degraded wetlands.
References. 1. Nankinov, 1985; 2. Dereliev, in press; 3. Kostadinova, Dereliev, 2001; 4. http://bspb.org; 5. Michev & Profirov, 2003; 6. Dontchev, 1973; 7. del Hoyo et al., 1992; 8. Paspaleva-Antonova, 1961; 9. Cramp & Simmons, 1977.
Authors: Sergei Dereliev, Bozhidar Ivanov
