Whiskered Tern

(Chlidonias hybrida)

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

Population size: 2020: 554 – 2037 pairs (2007: 220 – 800 pairs)

Distribution pattern

Dispersed and grouped mainly along the Danube River and in the Danubian Plain. With isolated breeding sites along the Black Sea coast, the Thracian Plain and the Sofia Field. These cases concern probably late migrants, which do not start breeding in the Danubian colonies until the end of June, when the rest of the pairs already have fully fledged juveniles. When water level at the breeding wetlands is too high, it forms small colonies at flooded grasslands of artificial wetlands, leading to changes in the distribution.

Population estimation for the period 2013 – 2020: During the period 2013-2020, the species was not found in nine squares, where it was found before 2013. Deterioration of some of the habitats explain their disappearance. In others, was observed sporadically, mainly during high water levels in the Danube River. New habitats have been established in 16 squares.

Population size in Special Protection Areas of Natura 2000: 554 – 1 907 pairs (94-100% of the population). The highest numbers have been registered in the Special Protection Areas “Belene Islands Complex” (197-570 pairs), “Kalimok Complex” (100-550 pairs) and “Srebarna” (83-220 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 marshes, in the exposed parts of floating aquatic vegetation, including in fishponds and other similar water bodies. During high waters, when the floating aquatic vegetation is submerged, breeds in temporary flooded meadows and other lowlands, which is not typical and is often associated with unsuccessful breeding.

Trends in population changes for the period 2013-2020

Threats

Drainage of wetlands, changes in the water level and in the hydrological regime of water bodies during the breeding season, disturbance.

Svilen Chesmedjiev, Petar Shurulinkov