Sterna sandvicensis (Latham, 1787)
Thalasseus sandvicensis Boie: Nankinov et al., 1997: 319; Simeonov, 1986: 75. Simeonov, Michev, 1991: 150.
Conservation status: in Bulgaria: Endangered EN D, BDA-II, III; International: BeC-II, BoC-II, ECS-Spec 2, BD-I.
General distribution. A cosmopolitan species with a scattered breeding area and total numbers of 460 000 – 500 000 individuals . On the European continent the subspecies St. s. sandvicensis breeds  in numbers less than 130 000 pairs) . The birds from the Black Sea winter in the Mediterranean region, Eastern Europe and Western Africa.
Distribution and abundance in Bulgaria. A breeding summer visitor and passage migrant. In the 70s and the 80s of the 19th century it bred along the Black Sea coast [5, 6], and after that it was registered only during migration [7, 8] or was not found at all . Multiplication was reported again in the 1980s in Atanasovsko Ezero lake [10, 11]. At present it breeds only there [13, 14] and in Pomoriysko Ezero lake . The numbers vary from singular birds to several hundred pairs  and depend on the condition of the places of breeding. Maximum numbers (1 269 breeding pairs) were registered in 1994 in Atanasovsko Ezero lake , and 1 310 breeding pairs in 2004 in Pomoriysko Lake . For the recent years the total numbers in the country are estimated at 680 breeding bairs.
Habitats. Salty shore lakes with sand bars.
Biology. It breeds in mixed colonies (with the Common Tern and the Gull-billed Tern, the Mediterranean Gull and the Avocet) on artificial islands or on dikes and hollows used in salt production. The nest is a hollow in the ground, without any building material . It flies into the multiplication sites at the end of April, and the multiplication season begins in May. It migrates in pairs and in flocks of up to about 50 individuals from April to the end of December . In rare cases also along the Bulgarian Black Sea shore. It feeds on small fish swimming near the surface, caught by swooping from a height of 5-10 m .
Similar species. The Gull-billed Tern (Gelochelrdon nilotica).
Negative factors. Destruction of the breeding places; collection of eggs; ground predators; high water levels; unregulated building; tourism; sports and fishing.
Conservation measures taken. Protected according to the Biological Diversity Act; building and maintenance of the artificial islands; carrying out monitoring and educational campaigns.
Conservation measures needed. Strict enforcement of the nature preservation legislation, regulation of the numbers of ground predators in the breeding places; continuation of the building and the maintenance of artificial islands; monitoring.
References. 1. Voons, 1960; 2. Wetlands International, 2002; 3. Dementev, 1951; 4. BirdLife International, 2004; 5. Elwes and Buckley, 1870; 6. Radakoff, 1879; 7. Reiser, 1894; 8. Patev, 1950; 9. Prostov, 1964; 10. Nankinov, Darakchiev, 1984; 11. Simeonov, 1986; 12. Gradev, 2003; 13. Enev, 1996; 14. Dimitrov et al., 2005; 15. Nankinov et al., 2004; 16. Green Balkans, 2006; 17. Nankinov et al., 1997; 18. Dunn, 1972.
Authors: Gradimir Gradev, Kiril Bedev, Milko Dimitrov, Hristo Nikolov, Pavel Simeonov