Strong declines of waders between 1991 and 2021 related to changes in water management in the Syvash wetlands

In the Azov-Black Sea region, the Syvash wetlands in Crimea and Kherson historically offer key staging and stopover areas for migratory waders of the African-Eurasian Flyway and Black Sea-Mediterranean Flyway. However, over time, significant changes in water management have taken place, channelling less irrigation water to the saline steppe lagoons, which has affected the habitats used by waders. In this paper we assess, for a 30-year period, changes in the abundance of migratory waders using the Syvash in spring and autumn, i.e. in April–May during northward migration and in August–September during southward migration. Large-scale counts were conducted in the 1990s and in 2004, followed by a series of partial counts in the 2000s, until a renewed, complete coverage of the Syvash area was achieved in spring and autumn of 2021, both for the Crimean and Kherson wetlands. The number of species recorded has declined. In 1991, in spring the area was used by 27 wader species (non-breeding, migratory species only), whereas in autumn 35 species were recorded. In 2021, 17 and 30 species were recorded in these seasons, respectively. While the abundance in spring was stable and possibly slowly increasing over the three decades (from 40,000 to 57,000 individuals), the abundance in autumn was much lower in 2004 and especially in 2021 than in the 1990s (down from 511,000 to 120,000 individuals). The reduction in abundance in autumn was observed in both Ramsar sites: Central and Eastern Syvash. We suggest that changes in the agroecosystem irrigation adjacent to Syvash is the main driver of population declines in autumn. Despite changes in hydrology and in the total numbers of waders, the Syvash wetlands are still regarded as one of the most important stopover sites for waders in Europe.