Common Tern

(Sterna hirundo)

Category of conservation concern (IUCN, 2020) – Least Concern

Population size: 2020: 1075 – 2340 pairs (2007: 500 – 1200 pairs)

Distribution pattern

With dispersed distribution, more grouped in places along the Black Sea coast (mainly in the Burgas Wetlands – 900 – 1500 pairs) and along the Danube River (on marshes along the banks and on islands, especially around the Belene Island 150 – 700 pairs). With single breeding sites on some larger inland rivers – Maritsa, Arda, Struma, Ogosta, etc. The colonies along the Danube River change their location due to the inconsistency of the breeding substratum – sandbars. From 20 to 60 pairs breed regularly in the Nikopol – Svishtov section, which are usually dispersed in small colonies, but during high water levels, they gather in one place.

Population estimation for the period 2013 – 2020: During the period 2013-2020, the species was found in 41 squares. Considerable increase in the breeding territory of the species is registered along the Danube River. Many new sites have also been established in the Upper Thracian Plain. During the study period, the localities along the Struma River have not been confirmed, but it is possible that the species has continued to nest there in the years.

The number of the species in the country is increasing in the traditional localities and in some other places, mainly in new small localities in different parts of the country. The main reason for this increase is the successful conservation measures implemented over the years in order to improve the breeding habitats of the species. In the Burgas Lakes, where the largest part of the breeding population of the country is found over the years up to 100% of the pairs breed on artificial platforms, built under nature protection projects. The lower waters of the Danube River, which is becoming a tendency, visibly has a positive effect on the species, creating many suitable for breeding sand islands.

Population size in Special Protection Areas of Natura 2000: 864 – 2097 pairs (80% of the population). All significant and regular breeding sites of the species are found on the territory of the Natura 2000 network. The highest numbers have been registered in the Special Protection Areas “Mandra-Poda Complex” (420 – 700 pairs), “Atanasovsko Lake” (221 – 600 pairs) and “Pomorie Lake” (200 – 500 pairs).

Comparative distribution of the species compared to the first breeding birds atlas (Iankov, 2007): Breeding locality until 2007 | Breeding locality until 2007, confirmed after 2015 – | New breeding locality after 2015. – The breeding localities after 2015 are identified on a base of raw data from smartbirds.org.

Habitats

Breeds in coastal lagoons (on dividing dikes and artificial islands in saltpans), in water–fringe vegetation in standing fresh waters, standing brackish waters, and on islands in running waters. Along the outfall of the Ropotamo River breeds on rocky islets in the sea.

Trends in population changes for the period 2013-2020

Threats

Predation (by stray dogs, jackals, yellow-legged gulls), threatening eggs and chicks in breeding colonies. Insufficient food (small fish), especially during the rearing period of the chicks. Extreme climate events because of global climate change. Destruction of nests and chicks due to technical activities in the production and extraction of salt. Sharp changes in the water level of rivers. Destruction of breeding habitats due to extraction of aggregates from riverbeds. Deepening and concreting of riverbeds.

Vladimir Mladenov, Ralitsa Georgieva, Petar Shurulinkov