Increased wind flood frequency leads to decreased nest success of endangered waders in managed shore meadows

Abstract

Climate change is expected to raise sea-levels and increase sea-level variation, which can have negative effects on the biodiversity of low-lying coastal areas. Using long-term mareograph (1970–2023) and breeding data (2002−22), we studied the occurrence of wind floods and their influence on breeding success in two endangered wading birds, the southern dunlin (Calidris alpina schinzii) and the ruff (Calidris pugnax) in managed coastal meadows in the northern Baltic Sea. In both species, flooding was an important cause of nest losses (dunlins 23.9 %, ruffs 21.4 %). Nest losses due to flooding increased from 10 % to 46 % during the 20-year dunlin study period, and from 9 % to 49 % during the seven-year ruff study period. Dunlins, but not ruffs, breed now closer to the shoreline than in the beginning of the study period. This can likely be explained by long-term overgrowth and increase in sward height in upper meadows due to lacking or inappropriate management. After a water level rise of 40 cm or more, flood losses in dunlins increased sharply, while in ruffs only moderately. Importantly, the frequency of floods reaching such critical levels has increased during the last 50 years. These flooding events require strong winds, but not actual storm winds. The increased flooding risk should be considered when planning the management of meadow habitats. Narrow elongated areas along shorelines should be avoided. Instead, management should secure attractive short growth habitats in the upper parts of meadows that are safe from flooding.