Gull-billed Tern
Sterna nilotica Gmelin, 1789
Gelochelidon nilotica (Gmelin, 1789): Nankinov et al, 1997: 311; Simeonov, Michev, 1981: 148; Sterna anglica (Montagu, 1813): Reiser, 1894: 197; Klain, 1909: 173.
Order Charadriiformes
Family Sternidae
Conservation status: in Bulgaria: Critically endangered CR=[A{1(a+c)+2(a+c)+4(a+c)}] + B[{1(a+b(ii+iii+v) + c(ii+iii+iv) + 2(b(ii+iv) + c(ii+iii+iv)}] + C[{1+2(a(i))}] + D, BDA-II, III; International: ECS-spec 3, vulnerable, BD-I, BeC-II.
General distribution. A cosmopolitan species with a scattered breeding area. The nominal subspecies S. n. nilotica inhabits Europe, Northwestern Africa and the Near East, Kazakhstan, Iran, Pakistan, India, Manchuria.
Distribution and abundance in Bulgaria. A breeding summer visitor and passage migrant, in the past only a rare migrant [1, 2]. In the 1950s it was registered for the first time as breeding in Atanasovsko Ezero lake [3]. It was there that the only permanent breeding habitat formed in the country, which in 1970-1980 had a relatively permanent abundance of 15-65 pairs [4, 5]. It was found breeding once in 1972 in the Pomoliysko lake [5]. After 1982 the numbers of the population sharply declined and since 1997 there no breeding has been reported [6]. During the multiplication season singular individuals and smaller or larger groups (up to 20 individuals) were registered in the Durankulak lake [7], the mouth of the river Batova [8], Vaya lake [9], along the Danube valley [5] and within the country [10; 11; 12]. During migration it is found in various wetlands [14].
Habitats. Supersalty basins; during migrations in freshwater, brackish and supersalty wetlands in the lower areas of the country.
Biology. It nests colonially on dikes, sand strips and small islands amidst vast water areas. It lays 3 eggs in a hollow on the ground. Its major food consists of different species of ground turtles, lizards, amphibians, small mouse-like rodents, the young of Laridae, waders and songbirds; less frequently small fishes and water invertebrates.
Similar species. The Sandwich Tern (Sterna sandvicensis).
Negative factors. Flooding of the nests, destruction of the incubation eggs and the clutches by ground predators, disturbance during dike repairs in Atanasovsko and Pomoriysko lakes, destruction or overgrowing with vegetation of the nest habitats; cannibalism.
Conservation measures taken. Protected according to the Biological Diversity Act. The major nest habitats are Protected Territories and Ramsar Sites.
Conservation measures needed. Regulation of the numbers of the ground predators; coordination of the repair activities on the dikes; building small islands and dikes in Atanasovsko and Pomoriysko lakes, the oxygenation lakes of LUKOIL, the Poda locality and the fisheries near the village of Cherni Vrah, Burgas region).
References. 1. Reiser, 1894; 2. Patev, 1950. 3. Prostov, 1957; 4. Michev, 1985; 5. Konigstedt, Robel, 1977; 6. Dimitrov et al., 2005; 7. Petrov, Zlatanov, 1955; 8. Liedel, Luther, 1969; 9. Mountfort, Ferguson-Lees, 1961; 10. Balat, 1962; 11. Simeonov, Sofroniev, 1968; 12. Nankinov, 1982; 13. Michev et al., 2004; 14. Hubalek, 1978.
Author: Milko Dimitrov
