Status of the Pallas’s Gull Ichthyaetus ichthyaetus during Summer/Autumn in the Fairway Volga–Kama Reservoirs (East European Plain) in Russia

The Pallas’s Gull Ichthyaetus ichthyaetus is a fish-eating predator listed in the category of recovering species of the Red Book of the Russian Federation. The purpose of the research was to study the state of the Pallasʹs Gull in the fairway (navigable zone) of the Volga–Kama reservoirs, in Russia and to assess their role in the current distribution of the species. In the summer and autumn of 2020–2022, at 11 reservoirs of the Volga and Kama rivers, counts of Pallasʹs Gulls were carried out from the bow deck of the R/V Akademik Topchiev. The transect length was 4633.5 km; the duration of observations was 364.3 h. A comprehensive bird count was applied in the direction of the vessel’s movement on transects with a fixed counting strip width of 200 m (100 m in each direction from the bow of the vessel). Birds were usually fixed on 30-min transects. The Pallas’s Gulls were found in 7 of the 11 reservoirs studied, and their status varied between common and very rare. The species was more abundant in the Gorky reservoir than in the Cheboksary, Kuibyshev, Saratov, and Nizhnekamsk reservoirs. The smallest abundance was recorded in the Volgograd and Rybinsk reservoirs. The Pallas’s Gull shows a steady annual presence on most reservoirs. The results indicate that in the Volga Basin, the range of Pallas’s Gull has expanded further north by more than 1000 km over the past 30 years from the species’ original areas of sustainable breeding in the North Caspian. Adult individuals of the Pallasʹs Gull (83.4% of the age composition of the population) play the main role in the dispersal. The most favorable clusters of the stable presence of the species were lake-shaped fragments of the Gorky and Kuibyshev reservoirs. On the territory of the East European Plain, the Volga–Kama reservoirs are important, if not decisive, in expanding the range of Pallas’s Gull to the north.