Analysis of Trends in the Abundance of Laridae Obtained in the Lagoons of the Western Coast of the Caspian Sea (Republic of Dagestan) in the Epoch of Climate Changes

The current decline in the number of waterfowl and semi-aquatic birds on a global scale is largely due to the reduction in the area of wetlands in the era of global warming. Using the example of transboundary populations of seagulls (order Charadriiformes, family Laridae), the data from long-term monitoring conducted in 1995–2020 in two key ornithological areas of international importance in Russia is presented: the Sulakskaya and Turalinskaya lagoons (Republic of Dagestan). The lagoons are located on one of the largest Western Caspian migratory route in Russia, which is arranged as a “bottleneck” where the flight paths of European and Asian migrants, which are part of the Black Sea-Mediterranean and West Siberian-East African flyways, are as close as possible. The Laridae model group, which includes 12 background taxa, was selected based on the regularity of their encounters during migration. Based on ring recovery data obtained from the Bird Ringing Center IEE RAS, the geographic dispersion of gull populations regularly migrating through the study areas was determined and the contour of their generalized flyway was designated. The share of each taxon was determined from the sum of all encountered individuals and the “core” of the species leading in numbers was identified. Correlation analysis showed that out of 12 gull taxa, 4 showed a significant increase in numbers, 3—decreased, and 5—remained at the same level. The obtained population trends were synchronized with the data from literary sources for the same species populations of Laridae, but in their nesting sites. The coincidence of the abundance trends obtained in the lagoons with the abundance trends of the same species/populations, but in their nesting sites, confirms the correctness of our assessment of the current state of the tested gull populations. Global warming affected the change in the timing of migration in 5 model taxa, while 5 species of gulls changed their migration routes in the Caspian region, changing their wintering range from African to Indian. A correlation between the abundance and intensity of Laridae migration with the average annual air temperature in the Caspian Lowland of Dagestan was found. It was shown that in warm years, the intensity of autumn migration and the abundance of gulls decreases, and in cold years it increases, while the population size themselves remains unchanged. Correlation analysis showed a reliable positive relationship between the increase in the number of common Caspian sprat, as one of the priority food items, with the increase in the number of 4 studied taxa. Correlation analysis also revealed a reliable link between the increase in the number of Laridae wintering in the study area and the regression of the Caspian Sea, in which shallow areas of the sea area improved the access of gulls to food resources (fish, benthos). Three key environmental factors that determine the dynamics of Laridae populations are discussed: hydroclimatic cycles, anthropogenic impact and foraging. The data obtained can serve as a basis for creating a Russian Laridae monitoring database with its subsequent integration with Eurasian databases. In order to preserve the biodiversity of the Turalinskaya Lagoon, including Laridae, it is recommended to create a regional protected area “Turalinskaya Lagoon.”