Increased Wind Flood Frequency Leads to Decreased Nest Success of Endangered Waders in Managed Shore Meadows

Abstract

AbstractClimate 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 and breeding data (2002-23), 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 %). Frequency of flood losses increased during the 20-year dunlin study period, and also in ruff during the seven-year period. Among dunlins, the probability of flood loss increased from 10% to 46%. Dunlins, but not ruffs, breed closer to the shoreline than earlier. Long-term overgrowth and increase in sward height in upper meadows due to lacking or inappropriate management most probably explain this. In Dunlin, flood losses increased sharply, in ruffs moderately, after the water rose 40 cm above normal levels, a level requiring strong but not actual storm winds. Importantly, the frequency of floods reaching such critical levels has increased during the last 50 years. 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 the meadows that are safe from flooding.

Keywords: climate change, wind floods, grassland management, seashore meadow restoration, habitat management, shorebirds